diff --git a/c_api/src/taichi_llvm_impl.h b/c_api/src/taichi_llvm_impl.h
index 84b3a899f3e30..a0c47eb360ce5 100644
--- a/c_api/src/taichi_llvm_impl.h
+++ b/c_api/src/taichi_llvm_impl.h
@@ -2,13 +2,11 @@
 
 #include "taichi_core_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class LlvmRuntimeExecutor;
 class MemoryPool;
 struct CompileConfig;
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 namespace capi {
 
diff --git a/docs/lang/articles/contribution/contributor_guide.md b/docs/lang/articles/contribution/contributor_guide.md
index b57835f55a23b..9a00d354d552d 100644
--- a/docs/lang/articles/contribution/contributor_guide.md
+++ b/docs/lang/articles/contribution/contributor_guide.md
@@ -313,7 +313,6 @@ Below we highlight some of the most widely used styles.
 - Constant names should use the camel case, with a prefix `k`, for example, `constexpr int kTaichiMaxNumArgs = 64;`.
 - Macros should start with `TI_`, for example, `TI_NOT_IMPLEMENTED`.
   - In general, avoid using macros as much as possible.
-  - Avoid using `TI_NAMESPACE_BEGIN/END` in the new code.
 
 ### Rule of thumbs
 
diff --git a/taichi/analysis/alias_analysis.cpp b/taichi/analysis/alias_analysis.cpp
index 517a39167d5ab..94f2b2f1369df 100644
--- a/taichi/analysis/alias_analysis.cpp
+++ b/taichi/analysis/alias_analysis.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass::analysis {
 
@@ -168,4 +168,4 @@ bool maybe_same_address(Stmt *var1, Stmt *var2) {
 
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/arithmetic_interpretor.cpp b/taichi/analysis/arithmetic_interpretor.cpp
index 5b00f15f6c8e1..c4210ad6145dd 100644
--- a/taichi/analysis/arithmetic_interpretor.cpp
+++ b/taichi/analysis/arithmetic_interpretor.cpp
@@ -7,8 +7,7 @@
 #include "taichi/ir/type_utils.h"
 #include "taichi/ir/visitors.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 using CodeRegion = ArithmeticInterpretor::CodeRegion;
@@ -180,5 +179,4 @@ std::optional<TypedConstant> ArithmeticInterpretor::evaluate(
   return ev.run(region, init_ctx);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/arithmetic_interpretor.h b/taichi/analysis/arithmetic_interpretor.h
index 3a40d14051419..4a1ea88f81c6f 100644
--- a/taichi/analysis/arithmetic_interpretor.h
+++ b/taichi/analysis/arithmetic_interpretor.h
@@ -7,8 +7,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/type.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 /**
  * Interprets a sequence of CHI IR statements within a block (acts like a
@@ -96,5 +95,4 @@ class ArithmeticInterpretor {
                                         const EvalContext &init_ctx) const;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/bls_analyzer.cpp b/taichi/analysis/bls_analyzer.cpp
index 2db07a0e7e0a1..6eb6ab54fe02d 100644
--- a/taichi/analysis/bls_analyzer.cpp
+++ b/taichi/analysis/bls_analyzer.cpp
@@ -3,8 +3,7 @@
 #include "taichi/system/profiler.h"
 #include "taichi/ir/analysis.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 BLSAnalyzer::BLSAnalyzer(OffloadedStmt *for_stmt, ScratchPads *pads)
     : for_stmt_(for_stmt), pads_(pads) {
@@ -106,5 +105,4 @@ bool BLSAnalyzer::run() {
   return analysis_ok_;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/bls_analyzer.h b/taichi/analysis/bls_analyzer.h
index 4986adff9572d..9bd0fcd66022a 100644
--- a/taichi/analysis/bls_analyzer.h
+++ b/taichi/analysis/bls_analyzer.h
@@ -4,8 +4,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/scratch_pad.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // Figure out accessed SNodes, and their ranges in this for stmt
 class BLSAnalyzer : public BasicStmtVisitor {
@@ -56,5 +55,4 @@ class BLSAnalyzer : public BasicStmtVisitor {
   bool analysis_ok_{true};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/build_cfg.cpp b/taichi/analysis/build_cfg.cpp
index 583303788a5b6..e23033f6fb285 100644
--- a/taichi/analysis/build_cfg.cpp
+++ b/taichi/analysis/build_cfg.cpp
@@ -3,8 +3,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/program/function.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 struct CFGFuncKey {
   FunctionKey func_key{"", -1, -1};
@@ -16,8 +15,7 @@ struct CFGFuncKey {
   }
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 namespace std {
 template <>
@@ -29,8 +27,7 @@ struct hash<taichi::lang::CFGFuncKey> {
 };
 }  // namespace std
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 /**
  * Build a control-flow graph. The resulting graph is guaranteed to have an
@@ -460,5 +457,4 @@ std::unique_ptr<ControlFlowGraph> build_cfg(IRNode *root) {
 }
 }  // namespace irpass::analysis
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/check_fields_registered.cpp b/taichi/analysis/check_fields_registered.cpp
index 6b417b0475eac..183568dde8331 100644
--- a/taichi/analysis/check_fields_registered.cpp
+++ b/taichi/analysis/check_fields_registered.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class FieldsRegisteredChecker : public BasicStmtVisitor {
  public:
@@ -33,4 +33,4 @@ void check_fields_registered(IRNode *root) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/clone.cpp b/taichi/analysis/clone.cpp
index e4c2476008da4..78d354369de8a 100644
--- a/taichi/analysis/clone.cpp
+++ b/taichi/analysis/clone.cpp
@@ -7,7 +7,7 @@
 
 #include <unordered_map>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class IRCloner : public IRVisitor {
  private:
@@ -139,4 +139,4 @@ std::unique_ptr<IRNode> clone(IRNode *root, Kernel *kernel) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/constexpr_propagation.cpp b/taichi/analysis/constexpr_propagation.cpp
index 88db1f84f9d43..6c620ec4fd111 100644
--- a/taichi/analysis/constexpr_propagation.cpp
+++ b/taichi/analysis/constexpr_propagation.cpp
@@ -4,7 +4,7 @@
 #include <unordered_set>
 #include <functional>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -106,4 +106,4 @@ std::unordered_set<Stmt *> constexpr_prop(
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/count_statements.cpp b/taichi/analysis/count_statements.cpp
index 78733878b0a3e..1f1a11828aa15 100644
--- a/taichi/analysis/count_statements.cpp
+++ b/taichi/analysis/count_statements.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Count all statements (including containers)
 class StmtCounter : public BasicStmtVisitor {
@@ -41,4 +41,4 @@ int count_statements(IRNode *root) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/data_source_analysis.cpp b/taichi/analysis/data_source_analysis.cpp
index 7c6721800f695..a3b47c873e114 100644
--- a/taichi/analysis/data_source_analysis.cpp
+++ b/taichi/analysis/data_source_analysis.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass::analysis {
 
@@ -77,4 +77,4 @@ std::vector<Stmt *> get_store_destination(Stmt *store_stmt) {
 
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/detect_fors_with_break.cpp b/taichi/analysis/detect_fors_with_break.cpp
index 7deefe34aff81..2a89161ae10ac 100644
--- a/taichi/analysis/detect_fors_with_break.cpp
+++ b/taichi/analysis/detect_fors_with_break.cpp
@@ -5,7 +5,7 @@
 
 #include <unordered_set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class DetectForsWithBreak : public BasicStmtVisitor {
  public:
@@ -50,4 +50,4 @@ std::unordered_set<Stmt *> detect_fors_with_break(IRNode *root) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_deactivations.cpp b/taichi/analysis/gather_deactivations.cpp
index d8979df79123f..0aa09ca8662b2 100644
--- a/taichi/analysis/gather_deactivations.cpp
+++ b/taichi/analysis/gather_deactivations.cpp
@@ -3,7 +3,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class GatherDeactivations : public BasicStmtVisitor {
  public:
@@ -36,4 +36,4 @@ std::unordered_set<SNode *> gather_deactivations(IRNode *root) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_mesh_thread_local.cpp b/taichi/analysis/gather_mesh_thread_local.cpp
index 41bc86a8aa953..da29ea10b906b 100644
--- a/taichi/analysis/gather_mesh_thread_local.cpp
+++ b/taichi/analysis/gather_mesh_thread_local.cpp
@@ -5,7 +5,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 using MeshElementTypeSet = std::unordered_set<mesh::MeshElementType>;
 
@@ -79,4 +79,4 @@ gather_mesh_thread_local(OffloadedStmt *offload, const CompileConfig &config) {
 
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_meshfor_relation_types.cpp b/taichi/analysis/gather_meshfor_relation_types.cpp
index 21ce9ef60f328..3168341944f06 100644
--- a/taichi/analysis/gather_meshfor_relation_types.cpp
+++ b/taichi/analysis/gather_meshfor_relation_types.cpp
@@ -5,7 +5,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass::analysis {
 
@@ -62,4 +62,4 @@ void gather_meshfor_relation_types(IRNode *node) {
 
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_snode_read_writes.cpp b/taichi/analysis/gather_snode_read_writes.cpp
index 270b6a88d074d..65743fdc1dda4 100644
--- a/taichi/analysis/gather_snode_read_writes.cpp
+++ b/taichi/analysis/gather_snode_read_writes.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass::analysis {
 
@@ -40,4 +40,4 @@ gather_snode_read_writes(IRNode *root) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_statements.cpp b/taichi/analysis/gather_statements.cpp
index 785afd0b767df..ddaf8844c7817 100644
--- a/taichi/analysis/gather_statements.cpp
+++ b/taichi/analysis/gather_statements.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class StmtSearcher : public BasicStmtVisitor {
  private:
@@ -37,4 +37,4 @@ std::vector<Stmt *> gather_statements(IRNode *root,
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_uniquely_accessed_pointers.cpp b/taichi/analysis/gather_uniquely_accessed_pointers.cpp
index e2cfd21af6f30..af258286c505f 100644
--- a/taichi/analysis/gather_uniquely_accessed_pointers.cpp
+++ b/taichi/analysis/gather_uniquely_accessed_pointers.cpp
@@ -5,7 +5,7 @@
 #include "taichi/ir/visitors.h"
 #include <algorithm>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class LoopUniqueStmtSearcher : public BasicStmtVisitor {
  private:
@@ -385,4 +385,4 @@ void gather_uniquely_accessed_bit_structs(IRNode *root, AnalysisManager *amgr) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_uniquely_accessed_pointers.h b/taichi/analysis/gather_uniquely_accessed_pointers.h
index 2314a5c5b8ede..489b5ac797f8e 100644
--- a/taichi/analysis/gather_uniquely_accessed_pointers.h
+++ b/taichi/analysis/gather_uniquely_accessed_pointers.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class GatherUniquelyAccessedBitStructsPass : public Pass {
  public:
@@ -16,5 +15,4 @@ class GatherUniquelyAccessedBitStructsPass : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gather_used_atomics.cpp b/taichi/analysis/gather_used_atomics.cpp
index cb1d8d32150ba..a37ce4e2623e4 100644
--- a/taichi/analysis/gather_used_atomics.cpp
+++ b/taichi/analysis/gather_used_atomics.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include <unordered_set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class UsedAtomicsSearcher : public BasicStmtVisitor {
  private:
@@ -49,4 +49,4 @@ std::unique_ptr<std::unordered_set<AtomicOpStmt *>> gather_used_atomics(
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/gen_offline_cache_key.cpp b/taichi/analysis/gen_offline_cache_key.cpp
index 5c1dfbef622f6..915fce3850f78 100644
--- a/taichi/analysis/gen_offline_cache_key.cpp
+++ b/taichi/analysis/gen_offline_cache_key.cpp
@@ -8,8 +8,7 @@
 #include "taichi/program/function.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 
@@ -656,5 +655,4 @@ void gen_offline_cache_key(Program *prog, IRNode *ast, std::ostream *os) {
   ASTSerializer::run(prog, ast, os);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/has_store_or_atomic.cpp b/taichi/analysis/has_store_or_atomic.cpp
index 391ee99fbba5a..27cb4c282eb11 100644
--- a/taichi/analysis/has_store_or_atomic.cpp
+++ b/taichi/analysis/has_store_or_atomic.cpp
@@ -3,7 +3,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Find if there is a store (or AtomicOpStmt).
 class LocalStoreSearcher : public BasicStmtVisitor {
@@ -54,4 +54,4 @@ bool has_store_or_atomic(IRNode *root, const std::vector<Stmt *> &vars) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/last_store_or_atomic.cpp b/taichi/analysis/last_store_or_atomic.cpp
index 4c90a094a11b1..63c444bf20c72 100644
--- a/taichi/analysis/last_store_or_atomic.cpp
+++ b/taichi/analysis/last_store_or_atomic.cpp
@@ -3,7 +3,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Find the **last** store, or return invalid if there is an AtomicOpStmt
 // after the last store.
@@ -121,4 +121,4 @@ std::pair<bool, Stmt *> last_store_or_atomic(IRNode *root, Stmt *var) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/mesh_bls_analyzer.cpp b/taichi/analysis/mesh_bls_analyzer.cpp
index 91ebc35b48da1..e9e461ec35ef5 100644
--- a/taichi/analysis/mesh_bls_analyzer.cpp
+++ b/taichi/analysis/mesh_bls_analyzer.cpp
@@ -3,8 +3,7 @@
 #include "taichi/system/profiler.h"
 #include "taichi/ir/analysis.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 MeshBLSAnalyzer::MeshBLSAnalyzer(OffloadedStmt *for_stmt,
                                  MeshBLSCaches *caches,
@@ -113,5 +112,4 @@ std::unique_ptr<MeshBLSCaches> initialize_mesh_local_attribute(
 }  // namespace analysis
 }  // namespace irpass
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/mesh_bls_analyzer.h b/taichi/analysis/mesh_bls_analyzer.h
index f8db1c3d2b9ba..d77b29500f666 100644
--- a/taichi/analysis/mesh_bls_analyzer.h
+++ b/taichi/analysis/mesh_bls_analyzer.h
@@ -7,8 +7,7 @@
 
 #include <set>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class MeshBLSCache {
  public:
@@ -154,5 +153,4 @@ class MeshBLSAnalyzer : public BasicStmtVisitor {
   CompileConfig config_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/offline_cache_util.cpp b/taichi/analysis/offline_cache_util.cpp
index ee41a3973784d..a39d4238e208d 100644
--- a/taichi/analysis/offline_cache_util.cpp
+++ b/taichi/analysis/offline_cache_util.cpp
@@ -11,8 +11,7 @@
 
 #include <vector>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 static std::vector<std::uint8_t> get_offline_cache_key_of_compile_config(
     CompileConfig *config) {
@@ -256,5 +255,4 @@ bool try_demangle_name(const std::string &mangled_name,
 
 }  // namespace offline_cache
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/offline_cache_util.h b/taichi/analysis/offline_cache_util.h
index 98a0c0d9f4f0a..1d13dd715261e 100644
--- a/taichi/analysis/offline_cache_util.h
+++ b/taichi/analysis/offline_cache_util.h
@@ -4,8 +4,7 @@
 
 #include "taichi/rhi/arch.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 struct CompileConfig;
 class Program;
@@ -28,5 +27,4 @@ bool try_demangle_name(const std::string &mangled_name,
 
 }  // namespace offline_cache
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/same_statements.cpp b/taichi/analysis/same_statements.cpp
index 9022e4cb9fd46..7fe6e1d557882 100644
--- a/taichi/analysis/same_statements.cpp
+++ b/taichi/analysis/same_statements.cpp
@@ -5,7 +5,7 @@
 #include <unordered_map>
 #include <unordered_set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Compare if two IRNodes are equivalent.
 class IRNodeComparator : public IRVisitor {
@@ -333,4 +333,4 @@ bool same_value(Stmt *stmt1,
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/analysis/value_diff.cpp b/taichi/analysis/value_diff.cpp
index c769895077a98..b8357cf69d2dc 100644
--- a/taichi/analysis/value_diff.cpp
+++ b/taichi/analysis/value_diff.cpp
@@ -5,8 +5,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/visitors.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 DiffRange operator+(const DiffRange &a, const DiffRange &b) {
   return DiffRange(a.related() && b.related(), a.coeff + b.coeff, a.low + b.low,
@@ -202,5 +201,4 @@ DiffPtrResult value_diff_ptr_index(Stmt *val1, Stmt *val2) {
 
 }  // namespace analysis
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/analysis/verify.cpp b/taichi/analysis/verify.cpp
index fd7c44c208cbf..684710b678efd 100644
--- a/taichi/analysis/verify.cpp
+++ b/taichi/analysis/verify.cpp
@@ -8,7 +8,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class IRVerifier : public BasicStmtVisitor {
  private:
@@ -150,4 +150,4 @@ void verify(IRNode *root) {
 }
 }  // namespace irpass::analysis
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/aot/graph_data.cpp b/taichi/aot/graph_data.cpp
index 47703f717c8e4..9d702bf08ad31 100644
--- a/taichi/aot/graph_data.cpp
+++ b/taichi/aot/graph_data.cpp
@@ -4,8 +4,7 @@
 
 #include <numeric>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace aot {
 
 void CompiledGraph::run(
@@ -81,5 +80,4 @@ void CompiledGraph::run(
   }
 }
 }  // namespace aot
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/aot/graph_data.h b/taichi/aot/graph_data.h
index 5f57a23ccc933..0ee1d18cd7028 100644
--- a/taichi/aot/graph_data.h
+++ b/taichi/aot/graph_data.h
@@ -11,8 +11,7 @@
 template <typename T, typename G>
 T taichi_union_cast_with_different_sizes(G g);
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class AotModuleBuilder;
 class Ndarray;
 class Texture;
@@ -165,5 +164,4 @@ struct TI_DLL_EXPORT CompiledGraph {
 };
 
 }  // namespace aot
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/aot/module_builder.cpp b/taichi/aot/module_builder.cpp
index 9c1a8a71fda0d..bdb5e53ef4b00 100644
--- a/taichi/aot/module_builder.cpp
+++ b/taichi/aot/module_builder.cpp
@@ -1,8 +1,7 @@
 #include "taichi/aot/module_builder.h"
 #include "taichi/program/kernel.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 void AotModuleBuilder::add(const std::string &identifier, Kernel *kernel) {
   add_per_backend(identifier, kernel);
@@ -62,5 +61,4 @@ void AotModuleBuilder::add_graph(const std::string &name,
   }
   graphs_[name] = graph;
 }
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/aot/module_builder.h b/taichi/aot/module_builder.h
index 6e44856444004..f9eb09ae7bd3e 100644
--- a/taichi/aot/module_builder.h
+++ b/taichi/aot/module_builder.h
@@ -9,8 +9,7 @@
 #include "taichi/aot/module_data.h"
 #include "taichi/aot/graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Kernel;
 class DataType;
@@ -83,5 +82,4 @@ class AotModuleBuilder {
   std::unordered_map<std::string, aot::CompiledGraph> graphs_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/aot/module_data.h b/taichi/aot/module_data.h
index 824de73fe6283..af15d3a249ae1 100644
--- a/taichi/aot/module_data.h
+++ b/taichi/aot/module_data.h
@@ -7,8 +7,7 @@
 #include "taichi/common/core.h"
 #include "taichi/common/serialization.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace aot {
 
 struct CompiledFieldData {
@@ -135,5 +134,4 @@ struct ModuleData {
 };
 
 }  // namespace aot
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/aot/module_loader.cpp b/taichi/aot/module_loader.cpp
index 7a611bd257eee..b321defffc39c 100644
--- a/taichi/aot/module_loader.cpp
+++ b/taichi/aot/module_loader.cpp
@@ -3,8 +3,7 @@
 #include "taichi/runtime/gfx/aot_module_loader_impl.h"
 #include "taichi/runtime/metal/aot_module_loader_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace aot {
 namespace {
 
@@ -84,5 +83,4 @@ Field *Module::get_snode_tree(const std::string &name) {
 }
 
 }  // namespace aot
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/aot/module_loader.h b/taichi/aot/module_loader.h
index 3ffe0d1a41842..ec60f4cb63abe 100644
--- a/taichi/aot/module_loader.h
+++ b/taichi/aot/module_loader.h
@@ -12,8 +12,7 @@
 #include "taichi/ir/snode.h"
 #include "taichi/aot/graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 struct RuntimeContext;
 class Graph;
@@ -166,5 +165,4 @@ class TargetDevice : public Device {
 };
 
 }  // namespace aot
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/cache/gfx/cache_manager.cpp b/taichi/cache/gfx/cache_manager.cpp
index f3284cee0f0c9..174798ee5ae26 100644
--- a/taichi/cache/gfx/cache_manager.cpp
+++ b/taichi/cache/gfx/cache_manager.cpp
@@ -9,8 +9,7 @@
 #include "taichi/util/lock.h"
 #include "taichi/util/offline_cache.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 
@@ -286,5 +285,4 @@ std::string CacheManager::make_kernel_key(CompileConfig *config,
 }
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/cache/gfx/cache_manager.h b/taichi/cache/gfx/cache_manager.h
index b99e2f888e05c..bf81855ad88cd 100644
--- a/taichi/cache/gfx/cache_manager.h
+++ b/taichi/cache/gfx/cache_manager.h
@@ -5,8 +5,7 @@
 #include "taichi/runtime/gfx/runtime.h"
 #include "taichi/util/offline_cache.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 class CacheManager {
@@ -51,5 +50,4 @@ class CacheManager {
 };
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/cc_kernel.h b/taichi/codegen/cc/cc_kernel.h
index 6ad9e70c8def5..e333e9451a50e 100644
--- a/taichi/codegen/cc/cc_kernel.h
+++ b/taichi/codegen/cc/cc_kernel.h
@@ -3,7 +3,7 @@
 #include "taichi/util/lang_util.h"
 #include <set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class Kernel;
 
@@ -41,4 +41,4 @@ class CCKernel {
 };
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/cc_layout.h b/taichi/codegen/cc/cc_layout.h
index 0a2f08cecb15b..37560e2f1b344 100644
--- a/taichi/codegen/cc/cc_layout.h
+++ b/taichi/codegen/cc/cc_layout.h
@@ -4,7 +4,7 @@
 
 class CCProgramImpl;
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace cccp {
 
 class CCLayout {
@@ -28,4 +28,4 @@ class CCLayout {
 };
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/cc_program.cpp b/taichi/codegen/cc/cc_program.cpp
index 42e579ddf0529..9a923d0405788 100644
--- a/taichi/codegen/cc/cc_program.cpp
+++ b/taichi/codegen/cc/cc_program.cpp
@@ -2,7 +2,7 @@
 
 using namespace taichi::lang::cccp;
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 CCProgramImpl::CCProgramImpl(CompileConfig &config) : ProgramImpl(config) {
   this->config = &config;
@@ -197,4 +197,4 @@ bool is_c_backend_available() {
 }
 };  // namespace cccp
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/cc_program.h b/taichi/codegen/cc/cc_program.h
index 53a19320a0b06..7c5e9c699836d 100644
--- a/taichi/codegen/cc/cc_program.h
+++ b/taichi/codegen/cc/cc_program.h
@@ -16,11 +16,11 @@
 #include <vector>
 #include <memory>
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 class DynamicLoader;
-TI_NAMESPACE_END
+}  // namespace taichi
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 using namespace taichi::lang::cccp;
 using CCFuncEntryType = void(cccp::CCContext *);
@@ -88,4 +88,4 @@ class CCProgramImpl : public ProgramImpl {
   uint64 *result_buffer_{nullptr};
   bool need_relink_{true};
 };
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/cc_runtime.h b/taichi/codegen/cc/cc_runtime.h
index 6d715dca135b6..bb75155ad432f 100644
--- a/taichi/codegen/cc/cc_runtime.h
+++ b/taichi/codegen/cc/cc_runtime.h
@@ -2,7 +2,7 @@
 
 #include "taichi/util/lang_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 class CCProgramImpl;
 
 namespace cccp {
@@ -31,4 +31,4 @@ class CCRuntime {
 };
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/cc_utils.h b/taichi/codegen/cc/cc_utils.h
index 7c0691b8c4018..9e8b15d4c0bf4 100644
--- a/taichi/codegen/cc/cc_utils.h
+++ b/taichi/codegen/cc/cc_utils.h
@@ -7,7 +7,7 @@
 #include <cstdlib>
 #include <iomanip>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace cccp {
 
 inline std::string cc_data_type_name(DataType dt) {
@@ -82,4 +82,4 @@ inline int execute(std::string fmt, Args &&...args) {
 }
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/codegen_cc.cpp b/taichi/codegen/cc/codegen_cc.cpp
index a271ec71cb7f0..b86b3034473db 100644
--- a/taichi/codegen/cc/codegen_cc.cpp
+++ b/taichi/codegen/cc/codegen_cc.cpp
@@ -11,7 +11,7 @@
 
 #define C90_COMPAT 0
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace cccp {  // Codegen for C Compiler Processor
 
 namespace {
@@ -605,4 +605,4 @@ std::unique_ptr<CCKernel> CCKernelGen::compile() {
 }
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/codegen_cc.h b/taichi/codegen/cc/codegen_cc.h
index 9b65f5b715357..d537e95e20215 100644
--- a/taichi/codegen/cc/codegen_cc.h
+++ b/taichi/codegen/cc/codegen_cc.h
@@ -3,7 +3,7 @@
 #include "taichi/util/lang_util.h"
 #include "taichi/codegen/codegen.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class CCProgramImpl;
 
@@ -28,4 +28,4 @@ class CCKernelGen {
 FunctionType compile_kernel(Kernel *kernel);
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/context.h b/taichi/codegen/cc/context.h
index 47207d0553a9a..0f44fa7c4ba3c 100644
--- a/taichi/codegen/cc/context.h
+++ b/taichi/codegen/cc/context.h
@@ -42,7 +42,7 @@ struct Ti_Context {
 #include "cc_program.h"
 #include "taichi/util/lang_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace cccp {
 
@@ -56,6 +56,6 @@ struct CCContext {
 
 };  // namespace cccp
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
 
 #endif  // _CC_INSIDE_KERNEL
diff --git a/taichi/codegen/cc/struct_cc.cpp b/taichi/codegen/cc/struct_cc.cpp
index ecb174fe37be8..83e1ebea24487 100644
--- a/taichi/codegen/cc/struct_cc.cpp
+++ b/taichi/codegen/cc/struct_cc.cpp
@@ -2,7 +2,7 @@
 #include "cc_layout.h"
 #include "cc_utils.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace cccp {
 
 void CCLayoutGen::generate_children(SNode *snode) {
@@ -47,4 +47,4 @@ std::unique_ptr<CCLayout> CCLayoutGen::compile() {
 }
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cc/struct_cc.h b/taichi/codegen/cc/struct_cc.h
index d8d6de175546d..2d0c59d6567e0 100644
--- a/taichi/codegen/cc/struct_cc.h
+++ b/taichi/codegen/cc/struct_cc.h
@@ -4,7 +4,7 @@
 #include "taichi/util/line_appender.h"
 #include "taichi/ir/snode.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 class CCProgramImpl;
 namespace cccp {
 
@@ -36,4 +36,4 @@ class CCLayoutGen {
 };
 
 }  // namespace cccp
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/codegen.cpp b/taichi/codegen/codegen.cpp
index b4e531a109c68..674cdd18d21ad 100644
--- a/taichi/codegen/codegen.cpp
+++ b/taichi/codegen/codegen.cpp
@@ -17,7 +17,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/analysis/offline_cache_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 KernelCodeGen::KernelCodeGen(Kernel *kernel, IRNode *ir)
     : prog(kernel->program), kernel(kernel), ir(ir) {
@@ -152,4 +152,4 @@ FunctionType ModuleToFunctionConverter::convert(const Kernel *kernel,
 }
 
 #endif
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/codegen.h b/taichi/codegen/codegen.h
index aafe0e04aa82d..9b72b1c99c5db 100644
--- a/taichi/codegen/codegen.h
+++ b/taichi/codegen/codegen.h
@@ -10,7 +10,7 @@
 #include "taichi/runtime/llvm/launch_arg_info.h"
 #include "taichi/codegen/llvm/llvm_codegen_utils.h"
 #endif
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class KernelCodeGen {
  protected:
@@ -68,4 +68,4 @@ class ModuleToFunctionConverter {
 };
 
 #endif
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cpu/codegen_cpu.cpp b/taichi/codegen/cpu/codegen_cpu.cpp
index a60337f7d1647..d7eae9508a7a2 100644
--- a/taichi/codegen/cpu/codegen_cpu.cpp
+++ b/taichi/codegen/cpu/codegen_cpu.cpp
@@ -11,7 +11,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/ir/analysis.h"
 #include "taichi/analysis/offline_cache_util.h"
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -290,4 +290,4 @@ FunctionType KernelCodeGenCPU::compile_to_function() {
       tlctx, get_llvm_program(prog)->get_runtime_executor());
   return converter.convert(kernel, compile_kernel_to_module());
 }
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cpu/codegen_cpu.h b/taichi/codegen/cpu/codegen_cpu.h
index 773a19a2f9dd8..14706ec6d9960 100644
--- a/taichi/codegen/cpu/codegen_cpu.h
+++ b/taichi/codegen/cpu/codegen_cpu.h
@@ -7,7 +7,7 @@
 #include "taichi/codegen/codegen.h"
 #include "taichi/codegen/llvm/codegen_llvm.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class KernelCodeGenCPU : public KernelCodeGen {
  public:
@@ -50,4 +50,4 @@ class CPUModuleToFunctionConverter : public ModuleToFunctionConverter {
 
 #endif
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cuda/codegen_cuda.cpp b/taichi/codegen/cuda/codegen_cuda.cpp
index a1f7f181bda5a..5265479aa9e8a 100644
--- a/taichi/codegen/cuda/codegen_cuda.cpp
+++ b/taichi/codegen/cuda/codegen_cuda.cpp
@@ -19,7 +19,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/transforms.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 using namespace llvm;
 
@@ -841,4 +841,4 @@ FunctionType CUDAModuleToFunctionConverter::convert(
 #endif  // TI_WITH_CUDA
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/cuda/codegen_cuda.h b/taichi/codegen/cuda/codegen_cuda.h
index 8fe6e1beb2b0b..c3dd73413cad4 100644
--- a/taichi/codegen/cuda/codegen_cuda.h
+++ b/taichi/codegen/cuda/codegen_cuda.h
@@ -5,7 +5,7 @@
 #include "taichi/codegen/codegen.h"
 #include "taichi/codegen/llvm/codegen_llvm.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class KernelCodeGenCUDA : public KernelCodeGen {
  public:
@@ -42,4 +42,4 @@ class CUDAModuleToFunctionConverter : public ModuleToFunctionConverter {
                        LLVMCompiledKernel data) const override;
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/dx12/codegen_dx12.cpp b/taichi/codegen/dx12/codegen_dx12.cpp
index 956f1873dc04b..be32c17c5c15f 100644
--- a/taichi/codegen/dx12/codegen_dx12.cpp
+++ b/taichi/codegen/dx12/codegen_dx12.cpp
@@ -14,7 +14,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/ir/analysis.h"
 #include "taichi/analysis/offline_cache_util.h"
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -283,4 +283,4 @@ FunctionType KernelCodeGenDX12::compile_to_function() {
   // FIXME: implement compile_to_function.
   return [](RuntimeContext &ctx) {};
 }
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/dx12/codegen_dx12.h b/taichi/codegen/dx12/codegen_dx12.h
index 5d352231a1e6b..740a55e13b9e0 100644
--- a/taichi/codegen/dx12/codegen_dx12.h
+++ b/taichi/codegen/dx12/codegen_dx12.h
@@ -8,7 +8,7 @@
 #include "taichi/codegen/llvm/codegen_llvm.h"
 #include "taichi/aot/module_data.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class KernelCodeGenDX12 : public KernelCodeGen {
  public:
@@ -29,4 +29,4 @@ class KernelCodeGenDX12 : public KernelCodeGen {
   FunctionType compile_to_function() override;
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/dx12/dx12_global_optimize_module.cpp b/taichi/codegen/dx12/dx12_global_optimize_module.cpp
index 316a295d5aea6..ad45b2d3e5ae4 100644
--- a/taichi/codegen/dx12/dx12_global_optimize_module.cpp
+++ b/taichi/codegen/dx12/dx12_global_optimize_module.cpp
@@ -35,8 +35,7 @@
 
 using namespace llvm;
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx12 {
 
 const char *NumWorkGroupsCBName = "num_work_groups.cbuf";
@@ -167,5 +166,4 @@ std::vector<uint8_t> global_optimize_module(llvm::Module *module,
 }
 
 }  // namespace directx12
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/dx12/dx12_llvm_passes.h b/taichi/codegen/dx12/dx12_llvm_passes.h
index 2821cead303d3..0da5b3e36a497 100644
--- a/taichi/codegen/dx12/dx12_llvm_passes.h
+++ b/taichi/codegen/dx12/dx12_llvm_passes.h
@@ -11,8 +11,7 @@ class Type;
 class GlobalVariable;
 }  // namespace llvm
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 struct CompileConfig;
 
 namespace directx12 {
@@ -30,8 +29,7 @@ std::vector<uint8_t> global_optimize_module(llvm::Module *module,
 extern const char *NumWorkGroupsCBName;
 
 }  // namespace directx12
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 namespace llvm {
 class ModulePass;
diff --git a/taichi/codegen/llvm/codegen_llvm.cpp b/taichi/codegen/llvm/codegen_llvm.cpp
index 3a7a5daa113ac..421ddb9552449 100644
--- a/taichi/codegen/llvm/codegen_llvm.cpp
+++ b/taichi/codegen/llvm/codegen_llvm.cpp
@@ -14,7 +14,7 @@
 #include "taichi/codegen/llvm/struct_llvm.h"
 #include "taichi/util/file_sequence_writer.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // TODO: sort function definitions to match declaration order in header
 
@@ -2750,6 +2750,6 @@ LLVMCompiledKernel LLVMCompiledKernel::clone() const {
   return {tasks, llvm::CloneModule(*module)};
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
 
 #endif  // #ifdef TI_WITH_LLVM
diff --git a/taichi/codegen/llvm/codegen_llvm.h b/taichi/codegen/llvm/codegen_llvm.h
index a02fcbb2c81e6..c783c8c58cbeb 100644
--- a/taichi/codegen/llvm/codegen_llvm.h
+++ b/taichi/codegen/llvm/codegen_llvm.h
@@ -12,8 +12,7 @@
 #include "taichi/codegen/llvm/llvm_compiled_data.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class TaskCodeGenLLVM;
 
@@ -396,7 +395,6 @@ class TaskCodeGenLLVM : public IRVisitor, public LLVMModuleBuilder {
   ~TaskCodeGenLLVM() override = default;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif  // #ifdef TI_WITH_LLVM
diff --git a/taichi/codegen/llvm/codegen_llvm_quant.cpp b/taichi/codegen/llvm/codegen_llvm_quant.cpp
index 23bcad019e07b..a5c425ccaa950 100644
--- a/taichi/codegen/llvm/codegen_llvm_quant.cpp
+++ b/taichi/codegen/llvm/codegen_llvm_quant.cpp
@@ -2,7 +2,7 @@
 #include "taichi/codegen/llvm/codegen_llvm.h"
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -591,6 +591,6 @@ llvm::Value *TaskCodeGenLLVM::reconstruct_quant_float(
   }
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
 
 #endif  // #ifdef TI_WITH_LLVM
diff --git a/taichi/codegen/llvm/llvm_codegen_utils.cpp b/taichi/codegen/llvm/llvm_codegen_utils.cpp
index 4ce6cff4a5b9f..99a06c403e61f 100644
--- a/taichi/codegen/llvm/llvm_codegen_utils.cpp
+++ b/taichi/codegen/llvm/llvm_codegen_utils.cpp
@@ -1,7 +1,6 @@
 #include "llvm_codegen_utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 std::string type_name(llvm::Type *type) {
   std::string type_name_str;
@@ -145,5 +144,4 @@ void check_func_call_signature(llvm::FunctionType *func_type,
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/llvm/llvm_codegen_utils.h b/taichi/codegen/llvm/llvm_codegen_utils.h
index 2c4cd6dfa2d8c..7a72b32d18131 100644
--- a/taichi/codegen/llvm/llvm_codegen_utils.h
+++ b/taichi/codegen/llvm/llvm_codegen_utils.h
@@ -36,8 +36,7 @@
 
 #include "taichi/runtime/llvm/llvm_context.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 inline constexpr char kLLVMPhysicalCoordinatesName[] = "PhysicalCoordinates";
 
@@ -187,5 +186,4 @@ class RuntimeObject {
   }
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/llvm/llvm_compiled_data.h b/taichi/codegen/llvm/llvm_compiled_data.h
index ccb3d66e5b8b8..93aaf5fe030a0 100644
--- a/taichi/codegen/llvm/llvm_compiled_data.h
+++ b/taichi/codegen/llvm/llvm_compiled_data.h
@@ -5,8 +5,7 @@
 
 #include "llvm/IR/Module.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class OffloadedTask {
  public:
@@ -56,5 +55,4 @@ struct LLVMCompiledKernel {
   TI_IO_DEF(tasks);
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/llvm/struct_llvm.cpp b/taichi/codegen/llvm/struct_llvm.cpp
index 62b986541e060..5fc60420bf263 100644
--- a/taichi/codegen/llvm/struct_llvm.cpp
+++ b/taichi/codegen/llvm/struct_llvm.cpp
@@ -7,8 +7,7 @@
 #include "taichi/struct/struct.h"
 #include "taichi/util/file_sequence_writer.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 StructCompilerLLVM::StructCompilerLLVM(Arch arch,
                                        const CompileConfig *config,
@@ -340,5 +339,4 @@ llvm::Function *StructCompilerLLVM::create_function(llvm::FunctionType *ft,
                                 *module);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/llvm/struct_llvm.h b/taichi/codegen/llvm/struct_llvm.h
index 5b418f8407bd4..381af3ead4173 100644
--- a/taichi/codegen/llvm/struct_llvm.h
+++ b/taichi/codegen/llvm/struct_llvm.h
@@ -5,8 +5,7 @@
 #include "taichi/codegen/llvm/llvm_codegen_utils.h"
 #include "taichi/struct/struct.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class LlvmProgramImpl;
 class StructCompilerLLVM : public StructCompiler, public LLVMModuleBuilder {
@@ -53,5 +52,4 @@ class StructCompilerLLVM : public StructCompiler, public LLVMModuleBuilder {
   int snode_tree_id_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/metal/codegen_metal.cpp b/taichi/codegen/metal/codegen_metal.cpp
index b3bab0357fa5d..b14cf49780aaa 100644
--- a/taichi/codegen/metal/codegen_metal.cpp
+++ b/taichi/codegen/metal/codegen_metal.cpp
@@ -14,8 +14,7 @@
 #include "taichi/math/arithmetic.h"
 #include "taichi/util/line_appender.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 namespace {
 
@@ -1711,5 +1710,4 @@ FunctionType compile_to_metal_executable(
 }
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/metal/codegen_metal.h b/taichi/codegen/metal/codegen_metal.h
index 373428c26a801..30d5a26b913aa 100644
--- a/taichi/codegen/metal/codegen_metal.h
+++ b/taichi/codegen/metal/codegen_metal.h
@@ -13,8 +13,7 @@
 #include "taichi/runtime/metal/kernel_utils.h"
 #include "taichi/codegen/metal/struct_metal.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 CompiledKernelData run_codegen(
@@ -35,5 +34,4 @@ FunctionType compile_to_metal_executable(
     OffloadedStmt *offloaded = nullptr);
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/metal/env_config.cpp b/taichi/codegen/metal/env_config.cpp
index 06b6f6bf38133..12cd0a15669df 100644
--- a/taichi/codegen/metal/env_config.cpp
+++ b/taichi/codegen/metal/env_config.cpp
@@ -3,7 +3,7 @@
 #include "taichi/util/lang_util.h"
 #include "taichi/util/environ_config.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace metal {
 
 EnvConfig::EnvConfig() {
@@ -18,4 +18,4 @@ const EnvConfig &EnvConfig::instance() {
 
 }  // namespace metal
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/metal/env_config.h b/taichi/codegen/metal/env_config.h
index 336facc2c40ee..ff726ddf0003b 100644
--- a/taichi/codegen/metal/env_config.h
+++ b/taichi/codegen/metal/env_config.h
@@ -2,7 +2,7 @@
 
 #include "taichi/util/lang_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace metal {
 
 // Metal specific config inferred from the environment.
@@ -27,4 +27,4 @@ class EnvConfig {
 
 }  // namespace metal
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/codegen/metal/struct_metal.cpp b/taichi/codegen/metal/struct_metal.cpp
index 56d6479e9964b..d583488da4c8d 100644
--- a/taichi/codegen/metal/struct_metal.cpp
+++ b/taichi/codegen/metal/struct_metal.cpp
@@ -14,8 +14,7 @@
 #include "taichi/math/arithmetic.h"
 #include "taichi/util/line_appender.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 namespace {
 namespace shaders {
@@ -430,5 +429,4 @@ CompiledRuntimeModule compile_runtime_module() {
 }
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/metal/struct_metal.h b/taichi/codegen/metal/struct_metal.h
index 5d4e0e1bebc2e..06170e756eb17 100644
--- a/taichi/codegen/metal/struct_metal.h
+++ b/taichi/codegen/metal/struct_metal.h
@@ -5,8 +5,7 @@
 
 #include "taichi/ir/snode.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 struct SNodeDescriptor {
@@ -93,5 +92,4 @@ struct CompiledRuntimeModule {
 CompiledRuntimeModule compile_runtime_module();
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/kernel_utils.cpp b/taichi/codegen/spirv/kernel_utils.cpp
index e7ad964dd8836..4a8ca257de198 100644
--- a/taichi/codegen/spirv/kernel_utils.cpp
+++ b/taichi/codegen/spirv/kernel_utils.cpp
@@ -7,8 +7,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace spirv {
 
 // static
@@ -127,5 +126,4 @@ KernelContextAttributes::KernelContextAttributes(const Kernel &kernel,
 }
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/kernel_utils.h b/taichi/codegen/spirv/kernel_utils.h
index 3dd005c8b17a5..99cda22a3cd61 100644
--- a/taichi/codegen/spirv/kernel_utils.h
+++ b/taichi/codegen/spirv/kernel_utils.h
@@ -9,8 +9,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/rhi/device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Kernel;
 class SNode;
@@ -274,5 +273,4 @@ struct TaichiKernelAttributes {
 };
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/snode_struct_compiler.cpp b/taichi/codegen/spirv/snode_struct_compiler.cpp
index 59b889331c5ff..498b76482364e 100644
--- a/taichi/codegen/spirv/snode_struct_compiler.cpp
+++ b/taichi/codegen/spirv/snode_struct_compiler.cpp
@@ -1,7 +1,6 @@
 #include "taichi/codegen/spirv/snode_struct_compiler.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace spirv {
 namespace {
 
@@ -174,5 +173,4 @@ CompiledSNodeStructs compile_snode_structs(SNode &root) {
 }
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/snode_struct_compiler.h b/taichi/codegen/spirv/snode_struct_compiler.h
index 2109ff5af7052..d2810d2110ed2 100644
--- a/taichi/codegen/spirv/snode_struct_compiler.h
+++ b/taichi/codegen/spirv/snode_struct_compiler.h
@@ -7,8 +7,7 @@
 
 #include "spirv_types.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace spirv {
 
 struct SNodeDescriptor {
@@ -60,5 +59,4 @@ struct CompiledSNodeStructs {
 CompiledSNodeStructs compile_snode_structs(SNode &root);
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/spirv_codegen.cpp b/taichi/codegen/spirv/spirv_codegen.cpp
index 2f549e86e943a..08f3cce1459da 100644
--- a/taichi/codegen/spirv/spirv_codegen.cpp
+++ b/taichi/codegen/spirv/spirv_codegen.cpp
@@ -17,8 +17,7 @@
 #include <spirv-tools/libspirv.hpp>
 #include <spirv-tools/optimizer.hpp>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace spirv {
 namespace {
 
@@ -2365,5 +2364,4 @@ void lower(Kernel *kernel) {
 }
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/spirv_codegen.h b/taichi/codegen/spirv/spirv_codegen.h
index 7a0e42cd8a666..3706918df55f8 100644
--- a/taichi/codegen/spirv/spirv_codegen.h
+++ b/taichi/codegen/spirv/spirv_codegen.h
@@ -8,8 +8,7 @@
 #include <spirv-tools/libspirv.hpp>
 #include <spirv-tools/optimizer.hpp>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Kernel;
 
@@ -42,5 +41,4 @@ class KernelCodegen {
 };
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/spirv_ir_builder.cpp b/taichi/codegen/spirv/spirv_ir_builder.cpp
index 5e0727144c1db..2fa13b459c6b3 100644
--- a/taichi/codegen/spirv/spirv_ir_builder.cpp
+++ b/taichi/codegen/spirv/spirv_ir_builder.cpp
@@ -1,8 +1,7 @@
 #include "taichi/codegen/spirv/spirv_ir_builder.h"
 #include "taichi/rhi/dx/dx_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace spirv {
 
@@ -1556,5 +1555,4 @@ void IRBuilder::init_random_function(Value global_tmp_) {
 }
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/spirv_ir_builder.h b/taichi/codegen/spirv/spirv_ir_builder.h
index 337985bad360b..3f5c280037cf3 100644
--- a/taichi/codegen/spirv/spirv_ir_builder.h
+++ b/taichi/codegen/spirv/spirv_ir_builder.h
@@ -10,8 +10,7 @@
 #include "taichi/rhi/device.h"
 #include "taichi/ir/statements.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace spirv {
 
 template <bool stop, std::size_t I, typename F>
@@ -641,5 +640,4 @@ class IRBuilder {
   std::vector<uint32_t> function_;
 };
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/spirv_types.cpp b/taichi/codegen/spirv/spirv_types.cpp
index d3830ff720778..cb964d4926d7e 100644
--- a/taichi/codegen/spirv/spirv_types.cpp
+++ b/taichi/codegen/spirv/spirv_types.cpp
@@ -1,8 +1,7 @@
 #include "spirv_types.h"
 #include "spirv_ir_builder.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace spirv {
 
 size_t StructType::memory_size(tinyir::LayoutContext &ctx) const {
@@ -473,5 +472,4 @@ std::unordered_map<const tinyir::Node *, uint32_t> ir_translate_to_spirv(
 }
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/spirv/spirv_types.h b/taichi/codegen/spirv/spirv_types.h
index 8870d697f6a55..880eb19555c29 100644
--- a/taichi/codegen/spirv/spirv_types.h
+++ b/taichi/codegen/spirv/spirv_types.h
@@ -3,8 +3,7 @@
 #include "lib_tiny_ir.h"
 #include "taichi/ir/type.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace spirv {
 
 class STD140LayoutContext : public tinyir::LayoutContext {};
@@ -241,5 +240,4 @@ std::unordered_map<const tinyir::Node *, uint32_t> ir_translate_to_spirv(
     IRBuilder *spir_builder);
 
 }  // namespace spirv
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/wasm/codegen_wasm.cpp b/taichi/codegen/wasm/codegen_wasm.cpp
index e9bce4571641c..f1474f82c1a63 100644
--- a/taichi/codegen/wasm/codegen_wasm.cpp
+++ b/taichi/codegen/wasm/codegen_wasm.cpp
@@ -11,8 +11,7 @@
 #include "taichi/util/file_sequence_writer.h"
 #include "taichi/runtime/program_impls/llvm/llvm_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 constexpr std::array<const char *, 5> kPreloadedFuncNames = {
@@ -292,5 +291,4 @@ LLVMCompiledKernel KernelCodeGenWASM::compile_kernel_to_module() {
   return tlctx->link_compiled_tasks(std::move(data));
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/codegen/wasm/codegen_wasm.h b/taichi/codegen/wasm/codegen_wasm.h
index f5e076dca5da2..31d195fc89753 100644
--- a/taichi/codegen/wasm/codegen_wasm.h
+++ b/taichi/codegen/wasm/codegen_wasm.h
@@ -8,8 +8,7 @@
 #include "llvm/IR/Module.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class KernelCodeGenWASM : public KernelCodeGen {
  public:
@@ -28,5 +27,4 @@ class KernelCodeGenWASM : public KernelCodeGen {
 #endif
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/common/core.cpp b/taichi/common/core.cpp
index 842a875300759..2f18f5a8309bd 100644
--- a/taichi/common/core.cpp
+++ b/taichi/common/core.cpp
@@ -18,7 +18,7 @@
 #include <unistd.h>
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 std::string python_package_dir;
 
@@ -105,4 +105,4 @@ int PID::get_parent_pid() {
 #endif
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/common/core.h b/taichi/common/core.h
index a66b50f18568f..316181bddb34a 100644
--- a/taichi/common/core.h
+++ b/taichi/common/core.h
@@ -105,20 +105,9 @@ static_assert(__cplusplus >= 201402L, "C++14 required.");
 
 #define TI_STATIC_ASSERT(x) static_assert((x), #x)
 
-#define TI_NAMESPACE_BEGIN namespace taichi {
-#define TI_NAMESPACE_END }
-
-#define TLANG_NAMESPACE_BEGIN \
-  namespace taichi {          \
-  namespace lang {
-
-#define TLANG_NAMESPACE_END \
-  }                         \
-  }
-
 void taichi_raise_assertion_failure_in_python(const char *msg);
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 //******************************************************************************
 //                                 System State
@@ -211,7 +200,7 @@ float64 constexpr operator"" _fd(unsigned long long v) {
   return float64(v);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 //******************************************************************************
 //                           Meta-programming
 //******************************************************************************
@@ -220,7 +209,7 @@ TI_NAMESPACE_END
 
 #include "taichi/common/logging.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 namespace zip {
 
@@ -276,7 +265,7 @@ inline bool starts_with(std::string const &str, std::string const &ending) {
     return std::equal(ending.begin(), ending.end(), str.begin());
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 //******************************************************************************
 //                               Serialization
@@ -288,7 +277,7 @@ TI_NAMESPACE_END
 //                                   Misc.
 //******************************************************************************
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 extern int __trash__;
 template <typename T>
@@ -342,4 +331,4 @@ class PID {
   static int get_parent_pid();
 };
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/common/dict.h b/taichi/common/dict.h
index c10818059e3e1..1cf63d376224b 100644
--- a/taichi/common/dict.h
+++ b/taichi/common/dict.h
@@ -17,7 +17,7 @@
 #include "taichi/common/core.h"
 #include "taichi/math/math.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 // Declare and then load
 // Load to `this`
@@ -354,4 +354,4 @@ inline bool Dict::get<bool>(std::string key) const {
 
 using Config = Dict;
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/common/exceptions.h b/taichi/common/exceptions.h
index ec7f65c3368ce..ace90e9b075cc 100644
--- a/taichi/common/exceptions.h
+++ b/taichi/common/exceptions.h
@@ -1,7 +1,6 @@
 #pragma once
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class IRModified {};
 
@@ -32,5 +31,4 @@ class TaichiAssertionError : public TaichiExceptionImpl {
   using TaichiExceptionImpl::TaichiExceptionImpl;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/common/interface.h b/taichi/common/interface.h
index d9ef18ae8ba04..098863c79fe7c 100644
--- a/taichi/common/interface.h
+++ b/taichi/common/interface.h
@@ -14,7 +14,7 @@
 #include <memory>
 #include <iostream>
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 template <typename T>
 std::shared_ptr<T> create_instance(const std::string &alias);
@@ -333,4 +333,4 @@ class InterfaceHolder {
     return alias;                                 \
   }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/common/serialization.h b/taichi/common/serialization.h
index 8458c1b7514d1..778fe7780b94c 100644
--- a/taichi/common/serialization.h
+++ b/taichi/common/serialization.h
@@ -20,10 +20,8 @@
 #include <vector>
 
 #ifdef TI_INCLUDED
-TI_NAMESPACE_BEGIN
+namespace taichi {
 #else
-#define TI_NAMESPACE_BEGIN
-#define TI_NAMESPACE_END
 #define TI_TRACE
 #define TI_CRITICAL
 #define TI_ASSERT assert
@@ -933,4 +931,6 @@ static_assert(
         std::vector<std::unique_ptr<int>> &>(),
     "");
 
-TI_NAMESPACE_END
+#ifdef TI_INCLUDED
+}  // namespace taichi
+#endif
diff --git a/taichi/common/task.h b/taichi/common/task.h
index d470c833edd7a..9ddd9d1655956 100644
--- a/taichi/common/task.h
+++ b/taichi/common/task.h
@@ -10,7 +10,7 @@
 
 #include "taichi/common/interface.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class Task : public Unit {
  public:
@@ -75,4 +75,4 @@ task_invoke(const T &func, const std::vector<std::string> &params) {
   };                                                                       \
   TI_IMPLEMENTATION(Task, Task_##task, #task)
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/ir/analysis.h b/taichi/ir/analysis.h
index 0b4ea3df62639..fcb3a9038ca7d 100644
--- a/taichi/ir/analysis.h
+++ b/taichi/ir/analysis.h
@@ -10,8 +10,7 @@
 #include <unordered_set>
 #include <unordered_map>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class DiffRange {
  private:
@@ -211,5 +210,4 @@ std::unique_ptr<MeshBLSCaches> initialize_mesh_local_attribute(
 
 }  // namespace analysis
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/basic_stmt_visitor.cpp b/taichi/ir/basic_stmt_visitor.cpp
index 989c71f35af46..71a33b051bfef 100644
--- a/taichi/ir/basic_stmt_visitor.cpp
+++ b/taichi/ir/basic_stmt_visitor.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 BasicStmtVisitor::BasicStmtVisitor() {
   allow_undefined_visitor = true;
@@ -68,4 +68,4 @@ void BasicStmtVisitor::visit(FrontendIfStmt *stmt) {
     stmt->false_statements->accept(this);
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/control_flow_graph.cpp b/taichi/ir/control_flow_graph.cpp
index 74f6e4311641f..ec15a17d6bf54 100644
--- a/taichi/ir/control_flow_graph.cpp
+++ b/taichi/ir/control_flow_graph.cpp
@@ -7,8 +7,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/system/profiler.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 CFGNode::CFGNode(Block *block,
                  int begin_location,
@@ -1026,5 +1025,4 @@ void ControlFlowGraph::determine_ad_stack_size(int default_ad_stack_size) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/control_flow_graph.h b/taichi/ir/control_flow_graph.h
index 1776a57ea4eea..d02f682b36e3c 100644
--- a/taichi/ir/control_flow_graph.h
+++ b/taichi/ir/control_flow_graph.h
@@ -5,8 +5,7 @@
 
 #include "taichi/ir/ir.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 /**
  * A basic block in control-flow graph.
@@ -168,5 +167,4 @@ class ControlFlowGraph {
   void determine_ad_stack_size(int default_ad_stack_size);
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/expr.cpp b/taichi/ir/expr.cpp
index 67c6566a4dad7..74e7c6f1d69ac 100644
--- a/taichi/ir/expr.cpp
+++ b/taichi/ir/expr.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/ir.h"
 #include "taichi/program/program.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 void Expr::set_tb(const std::string &tb) {
   expr->tb = tb;
@@ -120,4 +120,4 @@ Expr expr_matrix_field(const std::vector<Expr> &fields,
   return Expr::make<MatrixFieldExpression>(fields, element_shape);
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/expr.h b/taichi/ir/expr.h
index ba84faecd09a9..c692e634c832d 100644
--- a/taichi/ir/expr.h
+++ b/taichi/ir/expr.h
@@ -3,7 +3,7 @@
 #include "taichi/util/str.h"
 #include "taichi/ir/type_utils.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 struct CompileConfig;
 class Expression;
@@ -149,4 +149,4 @@ Expr expr_field(Expr id_expr, DataType dt);
 Expr expr_matrix_field(const std::vector<Expr> &fields,
                        const std::vector<int> &element_shape);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/expression.h b/taichi/ir/expression.h
index 1f400e5b24374..821ec3adfa6b3 100644
--- a/taichi/ir/expression.h
+++ b/taichi/ir/expression.h
@@ -5,7 +5,7 @@
 #include "taichi/ir/ir.h"
 #include "taichi/ir/expr.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class ExpressionVisitor;
 
@@ -162,4 +162,4 @@ class ExpressionVisitor {
     visitor->visit(this);                            \
   }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/expression_ops.h b/taichi/ir/expression_ops.h
index c939a520ac972..845c86cb6b0a7 100644
--- a/taichi/ir/expression_ops.h
+++ b/taichi/ir/expression_ops.h
@@ -73,8 +73,7 @@
 
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 DEFINE_EXPRESSION_FUNC_UNARY(sqrt)
 DEFINE_EXPRESSION_FUNC_UNARY(round)
@@ -126,8 +125,7 @@ DEFINE_EXPRESSION_FUNC_BINARY(bit_shr)
 DEFINE_EXPRESSION_FUNC_TERNARY(select)
 DEFINE_EXPRESSION_FUNC_TERNARY(ifte)
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #undef DEFINE_EXPRESSION_OP_UNARY
 #undef DEFINE_EXPRESSION_OP_BINARY
diff --git a/taichi/ir/expression_printer.h b/taichi/ir/expression_printer.h
index c0f595efc0f95..93cec54c6f882 100644
--- a/taichi/ir/expression_printer.h
+++ b/taichi/ir/expression_printer.h
@@ -6,8 +6,7 @@
 #include "taichi/program/program.h"
 #include "taichi/analysis/offline_cache_util.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class ExpressionPrinter : public ExpressionVisitor {
  public:
@@ -286,5 +285,4 @@ class ExpressionHumanFriendlyPrinter : public ExpressionPrinter {
   }
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/frontend_ir.cpp b/taichi/ir/frontend_ir.cpp
index 4b9503ebe04b8..55800d2b2d8b0 100644
--- a/taichi/ir/frontend_ir.cpp
+++ b/taichi/ir/frontend_ir.cpp
@@ -5,7 +5,7 @@
 #include "taichi/program/program.h"
 #include "taichi/common/exceptions.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 #define TI_ASSERT_TYPE_CHECKED(x)                       \
   TI_ASSERT_INFO(x->ret_type != PrimitiveType::unknown, \
@@ -1308,4 +1308,4 @@ void flatten_rvalue(Expr ptr, Expression::FlattenContext *ctx) {
   }
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/frontend_ir.h b/taichi/ir/frontend_ir.h
index 98e6c549f4b33..e61f29c255135 100644
--- a/taichi/ir/frontend_ir.h
+++ b/taichi/ir/frontend_ir.h
@@ -11,7 +11,7 @@
 #include "taichi/program/function.h"
 #include "taichi/ir/mesh.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 struct ForLoopConfig {
   bool is_bit_vectorized{false};
@@ -1041,4 +1041,4 @@ void flatten_lvalue(Expr expr, Expression::FlattenContext *ctx);
 
 void flatten_rvalue(Expr expr, Expression::FlattenContext *ctx);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/ir.cpp b/taichi/ir/ir.cpp
index 73c546000593c..089e29b94d307 100644
--- a/taichi/ir/ir.cpp
+++ b/taichi/ir/ir.cpp
@@ -8,8 +8,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/ir/transforms.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 std::string snode_access_flag_name(SNodeAccessFlag type) {
   if (type == SNodeAccessFlag::block_local) {
@@ -496,5 +495,4 @@ void DelayedIRModifier::mark_as_modified() {
   modified_ = true;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/ir.h b/taichi/ir/ir.h
index f52ed955d5193..6de386155be8c 100644
--- a/taichi/ir/ir.h
+++ b/taichi/ir/ir.h
@@ -20,8 +20,7 @@
 #include "llvm/ADT/MapVector.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class IRNode;
 class Block;
@@ -605,5 +604,4 @@ inline void StmtFieldManager::operator()(const char *key, T &&value) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/ir_builder.cpp b/taichi/ir/ir_builder.cpp
index 9285713e89fd2..59a66838dd663 100644
--- a/taichi/ir/ir_builder.cpp
+++ b/taichi/ir/ir_builder.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/common/logging.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -484,4 +484,4 @@ MeshPatchIndexStmt *IRBuilder::get_patch_index() {
   return insert(Stmt::make_typed<MeshPatchIndexStmt>());
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/ir_builder.h b/taichi/ir/ir_builder.h
index 0c0b2bf15e85d..41a52a285ff41 100644
--- a/taichi/ir/ir_builder.h
+++ b/taichi/ir/ir_builder.h
@@ -3,7 +3,7 @@
 #include "taichi/ir/ir.h"
 #include "taichi/ir/mesh.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class Function;
 
@@ -286,4 +286,4 @@ class IRBuilder {
   InsertPoint insert_point_;
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/mesh.cpp b/taichi/ir/mesh.cpp
index 9219c84c4da4a..4e14011f1362e 100644
--- a/taichi/ir/mesh.cpp
+++ b/taichi/ir/mesh.cpp
@@ -1,7 +1,6 @@
 #include "taichi/ir/mesh.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace mesh {
 
 std::string element_type_name(MeshElementType type) {
@@ -57,5 +56,4 @@ MeshRelationType inverse_relation(MeshRelationType rel) {
 }
 
 }  // namespace mesh
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/mesh.h b/taichi/ir/mesh.h
index cbae90c7d94cf..2393c6d941225 100644
--- a/taichi/ir/mesh.h
+++ b/taichi/ir/mesh.h
@@ -8,8 +8,7 @@
 
 #include <unordered_set>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Stmt;
 
@@ -93,5 +92,4 @@ struct MeshPtr {  // Mesh wrapper in python
 };
 
 }  // namespace mesh
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/offloaded_task_type.cpp b/taichi/ir/offloaded_task_type.cpp
index 3203c53796aba..164f7f0a07a76 100644
--- a/taichi/ir/offloaded_task_type.cpp
+++ b/taichi/ir/offloaded_task_type.cpp
@@ -1,6 +1,6 @@
 #include "taichi/ir/offloaded_task_type.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 std::string offloaded_task_type_name(OffloadedTaskType tt) {
   if (false) {
@@ -12,4 +12,4 @@ std::string offloaded_task_type_name(OffloadedTaskType tt) {
     TI_NOT_IMPLEMENTED
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/offloaded_task_type.h b/taichi/ir/offloaded_task_type.h
index 673a8164c2087..b79716e174320 100644
--- a/taichi/ir/offloaded_task_type.h
+++ b/taichi/ir/offloaded_task_type.h
@@ -4,8 +4,7 @@
 
 #include <string>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 enum class OffloadedTaskType : int {
 #define PER_TASK_TYPE(x) x,
@@ -15,5 +14,4 @@ enum class OffloadedTaskType : int {
 
 std::string offloaded_task_type_name(OffloadedTaskType tt);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/pass.cpp b/taichi/ir/pass.cpp
index 7f01501fe5d7f..55e2844085d6c 100644
--- a/taichi/ir/pass.cpp
+++ b/taichi/ir/pass.cpp
@@ -1,9 +1,7 @@
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 const PassID Pass::id = "undefined";
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/pass.h b/taichi/ir/pass.h
index 734de1e321870..e9f3e0902e0bb 100644
--- a/taichi/ir/pass.h
+++ b/taichi/ir/pass.h
@@ -7,8 +7,7 @@
 #include <typeindex>
 #include <utility>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 using PassID = std::string;
 
@@ -85,5 +84,4 @@ class AnalysisManager {
   std::unordered_map<PassID, std::unique_ptr<AnalysisResultConcept>> result_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/scratch_pad.cpp b/taichi/ir/scratch_pad.cpp
index 6d6a086d6325d..9484671cb4a47 100644
--- a/taichi/ir/scratch_pad.cpp
+++ b/taichi/ir/scratch_pad.cpp
@@ -2,7 +2,7 @@
 
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 std::string ScratchPad::global_to_linearized_local(
     const std::vector<Stmt *> &loop_vars,
@@ -19,4 +19,4 @@ std::string ScratchPad::global_to_linearized_local(
   return ret;
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/scratch_pad.h b/taichi/ir/scratch_pad.h
index 7df97db99a171..09a9c13282e10 100644
--- a/taichi/ir/scratch_pad.h
+++ b/taichi/ir/scratch_pad.h
@@ -2,7 +2,7 @@
 
 #include "taichi/ir/snode.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class Stmt;
 
@@ -258,4 +258,4 @@ class ScratchPads {
   }
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/snode.cpp b/taichi/ir/snode.cpp
index 751b5d753449b..6a4fe1f3890f0 100644
--- a/taichi/ir/snode.cpp
+++ b/taichi/ir/snode.cpp
@@ -7,7 +7,7 @@
 #include "taichi/program/program.h"
 #include "taichi/program/snode_rw_accessors_bank.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 std::atomic<int> SNode::counter{0};
 
@@ -361,4 +361,4 @@ int SNode::get_snode_tree_id() const {
   return snode_tree_id_;
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/snode.h b/taichi/ir/snode.h
index 1c646802b1be2..4c9ba69f53730 100644
--- a/taichi/ir/snode.h
+++ b/taichi/ir/snode.h
@@ -8,8 +8,7 @@
 #include "taichi/ir/type.h"
 #include "taichi/program/snode_expr_utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class Program;
 class SNodeRwAccessorsBank;
 
@@ -364,5 +363,4 @@ class SNode {
   SNodeRwAccessorsBank *snode_rw_accessors_bank_{nullptr};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/snode_types.cpp b/taichi/ir/snode_types.cpp
index 974c81df55dc5..829d6dc7a5caf 100644
--- a/taichi/ir/snode_types.cpp
+++ b/taichi/ir/snode_types.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/common/logging.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 std::string snode_type_name(SNodeType t) {
   switch (t) {
@@ -23,5 +22,4 @@ bool is_gc_able(SNodeType t) {
   return (t == SNodeType::pointer || t == SNodeType::dynamic);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/snode_types.h b/taichi/ir/snode_types.h
index 7a1a27c5af4af..8dbe7623e6aa8 100644
--- a/taichi/ir/snode_types.h
+++ b/taichi/ir/snode_types.h
@@ -2,8 +2,7 @@
 
 #include <string>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 enum class SNodeType {
 #define PER_SNODE(x) x,
@@ -15,5 +14,4 @@ std::string snode_type_name(SNodeType t);
 
 bool is_gc_able(SNodeType t);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/statements.cpp b/taichi/ir/statements.cpp
index 26b6c205fe098..4bdce35584169 100644
--- a/taichi/ir/statements.cpp
+++ b/taichi/ir/statements.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/util/bit.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 UnaryOpStmt::UnaryOpStmt(UnaryOpType op_type, Stmt *operand)
     : op_type(op_type), operand(operand) {
@@ -412,4 +412,4 @@ BitStructType *BitStructStoreStmt::get_bit_struct() const {
   return ptr->as<SNodeLookupStmt>()->snode->dt->as<BitStructType>();
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/statements.h b/taichi/ir/statements.h
index 89ec00a558167..71f4bf2222347 100644
--- a/taichi/ir/statements.h
+++ b/taichi/ir/statements.h
@@ -8,8 +8,7 @@
 
 #include <optional>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Function;
 
@@ -1841,5 +1840,4 @@ class MatrixInitStmt : public Stmt {
   TI_DEFINE_ACCEPT_AND_CLONE
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/stmt_op_types.cpp b/taichi/ir/stmt_op_types.cpp
index 9130797ce128d..64769b56bf55e 100644
--- a/taichi/ir/stmt_op_types.cpp
+++ b/taichi/ir/stmt_op_types.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/common/logging.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 std::string unary_op_type_name(UnaryOpType type) {
   switch (type) {
 #define PER_UNARY_OP(i) \
@@ -164,5 +163,4 @@ std::string texture_op_type_name(TextureOpType type) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/stmt_op_types.h b/taichi/ir/stmt_op_types.h
index f2c9ee681b6c2..30aa7a6425b92 100644
--- a/taichi/ir/stmt_op_types.h
+++ b/taichi/ir/stmt_op_types.h
@@ -4,8 +4,7 @@
 
 #include "taichi/common/core.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 enum class UnaryOpType : int {
 #define PER_UNARY_OP(x) x,
@@ -94,5 +93,4 @@ enum class TextureOpType : int {
 
 std::string texture_op_type_name(TextureOpType type);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/transforms.h b/taichi/ir/transforms.h
index 77ca33f2450cd..b46f94767b0eb 100644
--- a/taichi/ir/transforms.h
+++ b/taichi/ir/transforms.h
@@ -18,7 +18,7 @@
 #include "taichi/transforms/simplify.h"
 #include "taichi/common/trait.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class ScratchPads;
 
@@ -196,4 +196,4 @@ void compile_function(IRNode *ir,
                       bool start_from_ast);
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/type.cpp b/taichi/ir/type.cpp
index 5e7758086de37..df1d32b818a30 100644
--- a/taichi/ir/type.cpp
+++ b/taichi/ir/type.cpp
@@ -3,7 +3,7 @@
 #include "taichi/ir/type_factory.h"
 #include "taichi/ir/type_utils.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Note: these primitive types should never be freed. They are supposed to live
 // together with the process. This is a temporary solution. Later we should
@@ -418,4 +418,4 @@ float64 TypedConstant::val_cast_to_float64() const {
   }
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/type.h b/taichi/ir/type.h
index 064a7fb0e8462..80171bed51b8c 100644
--- a/taichi/ir/type.h
+++ b/taichi/ir/type.h
@@ -3,7 +3,7 @@
 #include "taichi/common/core.h"
 #include "taichi/util/bit.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class TensorType;
 
@@ -479,4 +479,4 @@ class TypedConstant {
   float64 val_cast_to_float64() const;
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/type_factory.cpp b/taichi/ir/type_factory.cpp
index 3ff41a59479e3..39bf6e1049189 100644
--- a/taichi/ir/type_factory.cpp
+++ b/taichi/ir/type_factory.cpp
@@ -2,7 +2,7 @@
 
 #include "taichi/ir/type_utils.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 TypeFactory &TypeFactory::get_instance() {
   static TypeFactory *type_factory = new TypeFactory;
@@ -188,4 +188,4 @@ DataType promoted_type(DataType x, DataType y) {
     return y;
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/type_factory.h b/taichi/ir/type_factory.h
index 3fa4ef3fb7aac..a273091579ea9 100644
--- a/taichi/ir/type_factory.h
+++ b/taichi/ir/type_factory.h
@@ -4,7 +4,7 @@
 
 #include <mutex>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class TypeFactory {
  public:
@@ -83,4 +83,4 @@ class TypeFactory {
 
 DataType promoted_type(DataType a, DataType b);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ir/type_utils.cpp b/taichi/ir/type_utils.cpp
index a86d8753a4441..b9ae8a0ab2a0f 100644
--- a/taichi/ir/type_utils.cpp
+++ b/taichi/ir/type_utils.cpp
@@ -1,7 +1,6 @@
 #include "taichi/ir/type_utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 std::string data_type_name(DataType t) {
   if (!t->is<PrimitiveType>()) {
@@ -138,5 +137,4 @@ std::string data_type_format(DataType dt) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/type_utils.h b/taichi/ir/type_utils.h
index bb3b56f23e614..a674a9b136607 100644
--- a/taichi/ir/type_utils.h
+++ b/taichi/ir/type_utils.h
@@ -3,8 +3,7 @@
 #include "taichi/ir/type.h"
 #include "taichi/ir/type_factory.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 std::vector<int> data_type_shape(DataType t);
 
@@ -270,5 +269,4 @@ class BitStructTypeBuilder {
   int current_shared_exponent_{-1};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/ir/visitors.h b/taichi/ir/visitors.h
index 1b1642054d889..20138e5f30450 100644
--- a/taichi/ir/visitors.h
+++ b/taichi/ir/visitors.h
@@ -1,7 +1,7 @@
 #pragma once
 #include "taichi/ir/ir.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Visits all non-containing statements
 class BasicStmtVisitor : public IRVisitor {
@@ -32,4 +32,4 @@ class BasicStmtVisitor : public IRVisitor {
   void visit(FrontendIfStmt *stmt) override;
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/jit/jit_module.h b/taichi/jit/jit_module.h
index 32fec986fb6e4..ca2e51b930629 100644
--- a/taichi/jit/jit_module.h
+++ b/taichi/jit/jit_module.h
@@ -7,7 +7,7 @@
 #include "taichi/util/lang_util.h"
 #include "taichi/program/kernel_profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // A architecture-specific JIT module that initializes with an **LLVM** module
 // and allows the user to call its functions
@@ -90,4 +90,4 @@ class JITModule {
   }
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/jit/jit_session.cpp b/taichi/jit/jit_session.cpp
index aa7890ad63256..3e3e514e714cd 100644
--- a/taichi/jit/jit_session.cpp
+++ b/taichi/jit/jit_session.cpp
@@ -4,7 +4,7 @@
 #include "llvm/IR/DataLayout.h"
 #endif
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 #ifdef TI_WITH_LLVM
 std::unique_ptr<JITSession> create_llvm_jit_session_cpu(
@@ -41,4 +41,4 @@ std::unique_ptr<JITSession> JITSession::create(TaichiLLVMContext *tlctx,
   return nullptr;
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/jit/jit_session.h b/taichi/jit/jit_session.h
index 898e1a0bb3614..4d5d8775b59bc 100644
--- a/taichi/jit/jit_session.h
+++ b/taichi/jit/jit_session.h
@@ -7,7 +7,7 @@
 #include "taichi/util/lang_util.h"
 #include "taichi/jit/jit_module.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Backend JIT compiler for all archs
 
@@ -45,4 +45,4 @@ class JITSession {
   virtual ~JITSession() = default;
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/math/array.h b/taichi/math/array.h
index 2b4e2e69903e6..6c8e66ba09c5b 100644
--- a/taichi/math/array.h
+++ b/taichi/math/array.h
@@ -7,7 +7,7 @@
 
 #include "array_2d.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 template <int dim>
 class IndexND;
 
@@ -17,4 +17,4 @@ class RegionND;
 template <int dim, typename T>
 class ArrayND;
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/math/array_2d.h b/taichi/math/array_2d.h
index 04633581a6fb3..97d3400104caa 100644
--- a/taichi/math/array_2d.h
+++ b/taichi/math/array_2d.h
@@ -14,7 +14,7 @@
 #include "array_fwd.h"
 #include "linalg.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 template <>
 class IndexND<2> {
@@ -794,4 +794,4 @@ inline void print(const Array2D<T> &arr) {
   arr.print("");
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/math/array_fwd.h b/taichi/math/array_fwd.h
index 23c8831a6d946..bfd2097d8d4ea 100644
--- a/taichi/math/array_fwd.h
+++ b/taichi/math/array_fwd.h
@@ -7,7 +7,7 @@
 
 #include "taichi/common/core.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 template <int dim>
 class IndexND;
@@ -27,4 +27,4 @@ class ArrayND;
 template <typename T, int dim>
 using TArray = ArrayND<dim, T>;
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/math/geometry_util.h b/taichi/math/geometry_util.h
index 3be56891a5de3..2238344721d99 100644
--- a/taichi/math/geometry_util.h
+++ b/taichi/math/geometry_util.h
@@ -10,7 +10,7 @@
 #include "taichi/common/core.h"
 #include "linalg.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 inline bool intersect(const Vector2 &a,
                       const Vector2 &b,
@@ -85,4 +85,4 @@ inline std::vector<Vector2> points_inside_sphere(std::vector<float> x_range,
   return ret;
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/math/linalg.h b/taichi/math/linalg.h
index a6c28d83eb859..809d0a70881a5 100644
--- a/taichi/math/linalg.h
+++ b/taichi/math/linalg.h
@@ -13,7 +13,7 @@
 #include "taichi/common/core.h"
 #include "scalar.h"
 #include "array_fwd.h"
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 // Instruction Set Extension
 
@@ -1448,4 +1448,4 @@ template <int N, typename T, InstSetExt ISE>
 struct is_MatrixND<MatrixND<N, T, ISE>> : public std::true_type {};
 }  // namespace type
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/math/math.h b/taichi/math/math.h
index b8bace82b6d5f..cc95add8af82b 100644
--- a/taichi/math/math.h
+++ b/taichi/math/math.h
@@ -10,7 +10,7 @@
 #include "array.h"
 #include "linalg.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 namespace math {
 template <typename T>
@@ -39,4 +39,4 @@ TI_FORCE_INLINE
 
 }  // namespace math
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/math/scalar.h b/taichi/math/scalar.h
index 1ce736428050a..33ca3f90b686c 100644
--- a/taichi/math/scalar.h
+++ b/taichi/math/scalar.h
@@ -8,7 +8,7 @@
 #include <cmath>
 #include "taichi/common/core.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 using std::abs;
 using std::acos;
@@ -170,4 +170,4 @@ inline int64 get_largest_pot(int64 a) noexcept {
   return a - (a >> 1);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/math/svd.h b/taichi/math/svd.h
index f57e081a1f0f8..e7d8e71334951 100644
--- a/taichi/math/svd.h
+++ b/taichi/math/svd.h
@@ -3,7 +3,7 @@
 #include "taichi/ir/ir.h"
 #include "taichi/ir/expression_ops.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 template <typename Tf, typename Ti>
 Expr svd_bitwise_or(const Expr &a, const Expr &b) {
@@ -903,4 +903,4 @@ sifakis_svd_export(ASTBuilder *ast_builder,
                          Sa11, Sa22, Sa33);
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/callable.cpp b/taichi/program/callable.cpp
index 0c8a1b1b148ee..d592400869dd1 100644
--- a/taichi/program/callable.cpp
+++ b/taichi/program/callable.cpp
@@ -1,8 +1,7 @@
 #include "taichi/program/callable.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 Callable::Callable() = default;
 
@@ -43,5 +42,4 @@ Callable::CurrentCallableGuard::~CurrentCallableGuard() {
   program_->current_callable = old_callable_;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/callable.h b/taichi/program/callable.h
index bfdc6ea3c6f60..658722cf1c2f3 100644
--- a/taichi/program/callable.h
+++ b/taichi/program/callable.h
@@ -2,8 +2,7 @@
 
 #include "taichi/util/lang_util.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Program;
 class IRNode;
@@ -105,5 +104,4 @@ class TI_DLL_EXPORT Callable {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/compile_config.cpp b/taichi/program/compile_config.cpp
index a3e022e47bd93..e28f80cda19e5 100644
--- a/taichi/program/compile_config.cpp
+++ b/taichi/program/compile_config.cpp
@@ -2,7 +2,7 @@
 
 #include <thread>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 CompileConfig::CompileConfig() {
   arch = host_arch();
@@ -71,4 +71,4 @@ CompileConfig::CompileConfig() {
   cc_link_cmd = "gcc -shared -fPIC -o '{}' '{}'";
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/compile_config.h b/taichi/program/compile_config.h
index 8868f7a642700..859044ed1ea54 100644
--- a/taichi/program/compile_config.h
+++ b/taichi/program/compile_config.h
@@ -3,8 +3,7 @@
 #include "taichi/rhi/arch.h"
 #include "taichi/util/lang_util.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 struct CompileConfig {
   Arch arch;
@@ -114,4 +113,4 @@ struct CompileConfig {
 
 extern TI_DLL_EXPORT CompileConfig default_compile_config;
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/context.h b/taichi/program/context.h
index ea2ecdb7c9f6a..6f44d1a27d9a3 100644
--- a/taichi/program/context.h
+++ b/taichi/program/context.h
@@ -4,8 +4,7 @@
 #include "taichi/inc/constants.h"
 
 #if defined(TI_RUNTIME_HOST)
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 #endif
 
 struct LLVMRuntime;
@@ -118,6 +117,5 @@ struct RuntimeContext {
 };
 
 #if defined(TI_RUNTIME_HOST)
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 #endif
diff --git a/taichi/program/extension.cpp b/taichi/program/extension.cpp
index 27a5a782c90cc..08ac31f64f847 100644
--- a/taichi/program/extension.cpp
+++ b/taichi/program/extension.cpp
@@ -3,7 +3,7 @@
 #include <unordered_map>
 #include <unordered_set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 bool is_extension_supported(Arch arch, Extension ext) {
   static std::unordered_map<Arch, std::unordered_set<Extension>> arch2ext = {
@@ -33,4 +33,4 @@ bool is_extension_supported(Arch arch, Extension ext) {
   return exts.find(ext) != exts.end();
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/extension.h b/taichi/program/extension.h
index 5cb81249c15ad..e842244752467 100644
--- a/taichi/program/extension.h
+++ b/taichi/program/extension.h
@@ -4,8 +4,7 @@
 
 #include <string>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // The Taichi core feature set (dense SNode) should probably be supported by all
 // the backends. In addition, each backend can optionally support features in
@@ -24,5 +23,4 @@ enum class Extension {
 
 bool is_extension_supported(Arch arch, Extension ext);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/function.cpp b/taichi/program/function.cpp
index 4513b28291a57..7241e7753e2de 100644
--- a/taichi/program/function.cpp
+++ b/taichi/program/function.cpp
@@ -3,8 +3,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/analysis/offline_cache_util.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 Function::Function(Program *program, const FunctionKey &func_key)
     : func_key(func_key) {
@@ -43,5 +42,4 @@ std::string Function::get_name() const {
   return func_key.get_full_name();
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/function.h b/taichi/program/function.h
index 4ebb6d2b964f5..2da23219d6c0c 100644
--- a/taichi/program/function.h
+++ b/taichi/program/function.h
@@ -3,8 +3,7 @@
 #include "taichi/program/callable.h"
 #include "taichi/program/function_key.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Program;
 
@@ -31,5 +30,4 @@ class Function : public Callable {
   std::optional<std::string> ast_serialization_data_;  // For generating AST-Key
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/function_key.cpp b/taichi/program/function_key.cpp
index c93f67d7b28cf..a102c83941f3f 100644
--- a/taichi/program/function_key.cpp
+++ b/taichi/program/function_key.cpp
@@ -1,7 +1,6 @@
 #include "taichi/program/function_key.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 FunctionKey::FunctionKey(const std::string &func_name,
                          int func_id,
@@ -18,5 +17,4 @@ std::string FunctionKey::get_full_name() const {
          std::to_string(instance_id);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/function_key.h b/taichi/program/function_key.h
index 2e8d7390aa5ca..eaa616e50f8a1 100644
--- a/taichi/program/function_key.h
+++ b/taichi/program/function_key.h
@@ -3,8 +3,7 @@
 #include <functional>
 #include <string>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 /**
  * A unique key of a function.
@@ -27,8 +26,7 @@ class FunctionKey {
   [[nodiscard]] std::string get_full_name() const;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 namespace std {
 template <>
diff --git a/taichi/program/graph_builder.cpp b/taichi/program/graph_builder.cpp
index 0dbaf0d588841..7cde479a831d9 100644
--- a/taichi/program/graph_builder.cpp
+++ b/taichi/program/graph_builder.cpp
@@ -2,8 +2,7 @@
 #include "taichi/program/ndarray.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 void Dispatch::compile(
     std::vector<aot::CompiledDispatch> &compiled_dispatches) {
   if (kernel_->compiled_aot_kernel() == nullptr) {
@@ -69,5 +68,4 @@ void GraphBuilder::dispatch(Kernel *kernel, const std::vector<aot::Arg> &args) {
   seq()->dispatch(kernel, args);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/graph_builder.h b/taichi/program/graph_builder.h
index d2dc64660a416..cc678d9bb682c 100644
--- a/taichi/program/graph_builder.h
+++ b/taichi/program/graph_builder.h
@@ -6,8 +6,7 @@
 #include "taichi/ir/type.h"
 #include "taichi/aot/graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class Kernel;
 class GraphBuilder;
 
@@ -77,5 +76,4 @@ class GraphBuilder {
   std::vector<std::unique_ptr<Node>> all_nodes_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/ir_node_extended_impl.cpp b/taichi/program/ir_node_extended_impl.cpp
index c004c6bca75aa..d91b25d9fb1fa 100644
--- a/taichi/program/ir_node_extended_impl.cpp
+++ b/taichi/program/ir_node_extended_impl.cpp
@@ -7,8 +7,7 @@
 // order to use files under "taichi/program". Ideally, we should:
 // 1. Have a dedicated IR compile config that lives under "taichi/ir"
 // 2. Just don't hook IRNode with a Kernel
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 Kernel *IRNode::get_kernel() const {
   return const_cast<IRNode *>(this)->get_ir_root()->kernel;
@@ -18,5 +17,4 @@ CompileConfig &IRNode::get_config() const {
   return get_kernel()->program->this_thread_config();
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/kernel.cpp b/taichi/program/kernel.cpp
index e66261015cd16..abedf47778423 100644
--- a/taichi/program/kernel.cpp
+++ b/taichi/program/kernel.cpp
@@ -15,7 +15,7 @@
 #include "taichi/runtime/program_impls/llvm/llvm_program.h"
 #endif
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class Function;
 
@@ -442,4 +442,4 @@ void Kernel::offload_to_executable(IRNode *stmt) {
       is_extension_supported(config.arch, Extension::bls) &&
           config.make_block_local);
 }
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/kernel.h b/taichi/program/kernel.h
index 5c74e4ae15e29..4c7bca71030a6 100644
--- a/taichi/program/kernel.h
+++ b/taichi/program/kernel.h
@@ -9,7 +9,7 @@
 #include "taichi/program/texture.h"
 #include "taichi/aot/graph_data.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class Program;
 
@@ -168,4 +168,4 @@ class TI_DLL_EXPORT Kernel : public Callable {
   bool from_cache_{false};
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/kernel_profiler.cpp b/taichi/program/kernel_profiler.cpp
index 40978f6a802b0..aecc0f36b8f54 100644
--- a/taichi/program/kernel_profiler.cpp
+++ b/taichi/program/kernel_profiler.cpp
@@ -5,7 +5,7 @@
 #include "taichi/rhi/cuda/cuda_profiler.h"
 #include "taichi/system/timeline.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 void KernelProfileStatisticalResult::insert_record(double t) {
   if (counter == 0) {
@@ -130,4 +130,4 @@ std::unique_ptr<KernelProfilerBase> make_profiler(Arch arch, bool enable) {
   }
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/kernel_profiler.h b/taichi/program/kernel_profiler.h
index 660935a0fd888..b116856a8dd38 100644
--- a/taichi/program/kernel_profiler.h
+++ b/taichi/program/kernel_profiler.h
@@ -10,7 +10,7 @@
 #include <memory>
 #include <regex>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 struct KernelProfileTracedRecord {
   // kernel attributes
@@ -105,4 +105,4 @@ class KernelProfilerBase {
 
 std::unique_ptr<KernelProfilerBase> make_profiler(Arch arch, bool enable);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/ndarray.cpp b/taichi/program/ndarray.cpp
index 15121a3fe231a..67d4ee2eaf86e 100644
--- a/taichi/program/ndarray.cpp
+++ b/taichi/program/ndarray.cpp
@@ -8,8 +8,7 @@
 #include "taichi/runtime/program_impls/llvm/llvm_program.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 
@@ -204,5 +203,4 @@ void Ndarray::write_float(const std::vector<int> &i, float64 val) {
   write<float>(i, val);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/ndarray.h b/taichi/program/ndarray.h
index 46bd41c1cb72c..aeac269bbd44d 100644
--- a/taichi/program/ndarray.h
+++ b/taichi/program/ndarray.h
@@ -7,8 +7,7 @@
 #include "taichi/ir/type_utils.h"
 #include "taichi/rhi/device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Program;
 class NdarrayRwAccessorsBank;
@@ -81,5 +80,4 @@ class TI_DLL_EXPORT Ndarray {
   Program *prog_{nullptr};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/parallel_executor.cpp b/taichi/program/parallel_executor.cpp
index 71b1fcb6bf1ef..84c804e6bb590 100644
--- a/taichi/program/parallel_executor.cpp
+++ b/taichi/program/parallel_executor.cpp
@@ -1,7 +1,7 @@
 #include <taichi/system/timeline.h>
 #include "taichi/program/parallel_executor.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 ParallelExecutor::ParallelExecutor(const std::string &name, int num_threads)
     : name_(name),
@@ -116,4 +116,4 @@ void ParallelExecutor::worker_loop() {
     }
   }
 }
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/parallel_executor.h b/taichi/program/parallel_executor.h
index 468253417fa51..d3b4473363cdf 100644
--- a/taichi/program/parallel_executor.h
+++ b/taichi/program/parallel_executor.h
@@ -10,7 +10,7 @@
 #include <unordered_map>
 #include "taichi/common/core.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 class ParallelExecutor {
  public:
   using TaskType = std::function<void()>;
@@ -62,4 +62,4 @@ class ParallelExecutor {
   // callback to be executed?
   std::condition_variable flush_cv_;
 };
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/program/program.cpp b/taichi/program/program.cpp
index 41bc7dffd7334..c99a15528bd99 100644
--- a/taichi/program/program.cpp
+++ b/taichi/program/program.cpp
@@ -45,8 +45,7 @@
 #include <xmmintrin.h>
 #endif  // defined(_M_X64) || defined(__x86_64)
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 std::atomic<int> Program::num_instances_;
 
 Program::Program(Arch desired_arch) : snode_rw_accessors_bank_(this) {
@@ -558,5 +557,4 @@ void Program::enqueue_compute_op_lambda(
   program_impl_->enqueue_compute_op_lambda(op, image_refs);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/program.h b/taichi/program/program.h
index 568567a7a628c..f34fef2029948 100644
--- a/taichi/program/program.h
+++ b/taichi/program/program.h
@@ -30,8 +30,7 @@
 #include "taichi/program/sparse_matrix.h"
 #include "taichi/ir/mesh.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 struct JITEvaluatorId {
   std::thread::id thread_id;
@@ -57,8 +56,7 @@ struct JITEvaluatorId {
   }
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 namespace std {
 template <>
@@ -72,8 +70,7 @@ struct hash<taichi::lang::JITEvaluatorId> {
 };
 }  // namespace std
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class StructCompiler;
 
@@ -400,5 +397,4 @@ class TI_DLL_EXPORT Program {
   std::vector<std::unique_ptr<Texture>> textures_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/program_impl.cpp b/taichi/program/program_impl.cpp
index 2838c3c2f152e..144f3b21b161a 100644
--- a/taichi/program/program_impl.cpp
+++ b/taichi/program/program_impl.cpp
@@ -1,7 +1,6 @@
 #include "program_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 ProgramImpl::ProgramImpl(CompileConfig &config_) : config(&config_) {
 }
@@ -11,5 +10,4 @@ void ProgramImpl::compile_snode_tree_types(SNodeTree *tree) {
   TI_NOT_IMPLEMENTED;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/program_impl.h b/taichi/program/program_impl.h
index 4f2a5d5a47381..760c4309fae86 100644
--- a/taichi/program/program_impl.h
+++ b/taichi/program/program_impl.h
@@ -10,8 +10,7 @@
 #include "taichi/rhi/device.h"
 #include "taichi/aot/graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // Represents an image resource reference for a compute/render Op
 struct ComputeOpImageRef {
@@ -164,5 +163,4 @@ class ProgramImpl {
  private:
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/snode_expr_utils.cpp b/taichi/program/snode_expr_utils.cpp
index e781ef477c969..bd73f820a86a8 100644
--- a/taichi/program/snode_expr_utils.cpp
+++ b/taichi/program/snode_expr_utils.cpp
@@ -2,8 +2,7 @@
 #include "taichi/ir/snode.h"
 #include "taichi/ir/frontend_ir.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 
@@ -101,5 +100,4 @@ void make_lazy_place(SNode *snode,
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/snode_expr_utils.h b/taichi/program/snode_expr_utils.h
index 6e933dd40a7d7..c0de9474cb496 100644
--- a/taichi/program/snode_expr_utils.h
+++ b/taichi/program/snode_expr_utils.h
@@ -9,8 +9,7 @@
 // given SNode. Expr is part of the frontend, which somehow depends on the
 // files inside "taichi/program". To make SNode fairly low-level and depend
 // on less, we thus move SNode-Expr related utils away from SNode itself.
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class Expr;
 class SNode;
 class FieldExpression;
@@ -29,5 +28,4 @@ void make_lazy_place(SNode *snode,
                      const std::function<void(std::unique_ptr<SNode> &,
                                               std::vector<Expr> &)> &collect);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/snode_rw_accessors_bank.cpp b/taichi/program/snode_rw_accessors_bank.cpp
index 97336b84a59b7..b5ccd0c4822d7 100644
--- a/taichi/program/snode_rw_accessors_bank.cpp
+++ b/taichi/program/snode_rw_accessors_bank.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 void set_kernel_args(const std::vector<int> &I,
@@ -79,5 +78,4 @@ uint64 SNodeRwAccessorsBank::Accessors::read_uint(const std::vector<int> &I) {
   return (uint64)read_int(I);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/snode_rw_accessors_bank.h b/taichi/program/snode_rw_accessors_bank.h
index c26ae6b630493..9a424c86a1fe4 100644
--- a/taichi/program/snode_rw_accessors_bank.h
+++ b/taichi/program/snode_rw_accessors_bank.h
@@ -5,8 +5,7 @@
 #include "taichi/program/kernel.h"
 #include "taichi/ir/snode.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Program;
 
@@ -56,5 +55,4 @@ class SNodeRwAccessorsBank {
   std::unordered_map<const SNode *, RwKernels> snode_to_kernels_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/sparse_matrix.cpp b/taichi/program/sparse_matrix.cpp
index af11862dafe06..23ca3371057e4 100644
--- a/taichi/program/sparse_matrix.cpp
+++ b/taichi/program/sparse_matrix.cpp
@@ -57,8 +57,7 @@ void print_triplet_from_csr(int64_t n_rows,
 
 }  // namespace
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 SparseMatrixBuilder::SparseMatrixBuilder(int rows,
                                          int cols,
@@ -647,5 +646,4 @@ const std::string CuSparseMatrix::to_string() const {
   return ostr.str();
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/sparse_matrix.h b/taichi/program/sparse_matrix.h
index 2065703bdb252..90f4a49d1dad9 100644
--- a/taichi/program/sparse_matrix.h
+++ b/taichi/program/sparse_matrix.h
@@ -9,8 +9,7 @@
 
 #include "Eigen/Sparse"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class SparseMatrix;
 
@@ -296,5 +295,4 @@ void make_sparse_matrix_from_ndarray_cusparse(Program *prog,
                                               const Ndarray &row_indices,
                                               const Ndarray &col_indices,
                                               const Ndarray &values);
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/sparse_solver.cpp b/taichi/program/sparse_solver.cpp
index bb4ea6c784e57..06d29f26ea0ba 100644
--- a/taichi/program/sparse_solver.cpp
+++ b/taichi/program/sparse_solver.cpp
@@ -26,8 +26,7 @@ struct key_hash {
 };
 }  // namespace
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 #define GET_EM(sm) \
   const EigenMatrix *mat = (const EigenMatrix *)(sm.get_matrix());
@@ -284,5 +283,4 @@ std::unique_ptr<SparseSolver> make_cusparse_solver(
     const std::string &ordering) {
   return std::make_unique<CuSparseSolver>();
 }
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/sparse_solver.h b/taichi/program/sparse_solver.h
index 460bdce0a6cea..96e19a2e896c3 100644
--- a/taichi/program/sparse_solver.h
+++ b/taichi/program/sparse_solver.h
@@ -6,8 +6,7 @@
 
 #include "sparse_matrix.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class SparseSolver {
  public:
@@ -75,5 +74,4 @@ std::unique_ptr<SparseSolver> make_cusparse_solver(
     DataType dt,
     const std::string &solver_type,
     const std::string &ordering);
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/texture.cpp b/taichi/program/texture.cpp
index 00c4b30276f1f..d1648d0c8c083 100644
--- a/taichi/program/texture.cpp
+++ b/taichi/program/texture.cpp
@@ -4,8 +4,7 @@
 #include "taichi/rhi/device.h"
 #include "taichi/ir/snode.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 Texture::Texture(Program *prog,
                  BufferFormat format,
@@ -134,5 +133,4 @@ Texture::~Texture() {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/program/texture.h b/taichi/program/texture.h
index 7b439a79eac40..5d6539e4a810c 100644
--- a/taichi/program/texture.h
+++ b/taichi/program/texture.h
@@ -7,8 +7,7 @@
 #include "taichi/ir/type_utils.h"
 #include "taichi/rhi/device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Program;
 class Ndarray;
@@ -66,5 +65,4 @@ class TI_DLL_EXPORT Texture {
   Program *prog_{nullptr};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/python/exception.cpp b/taichi/python/exception.cpp
index 2154ec0762428..b87ec76062f00 100644
--- a/taichi/python/exception.cpp
+++ b/taichi/python/exception.cpp
@@ -5,13 +5,13 @@
 
 #include "taichi/python/exception.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void raise_assertion_failure_in_python(const std::string &msg) {
   throw ExceptionForPython(msg);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 void taichi_raise_assertion_failure_in_python(const char *msg) {
   taichi::raise_assertion_failure_in_python(std::string(msg));
diff --git a/taichi/python/exception.h b/taichi/python/exception.h
index 1397f2070631c..6df68d2860762 100644
--- a/taichi/python/exception.h
+++ b/taichi/python/exception.h
@@ -9,7 +9,7 @@
 
 #include <exception>
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class ExceptionForPython : public std::exception {
  private:
@@ -25,4 +25,4 @@ class ExceptionForPython : public std::exception {
 
 void raise_assertion_failure_in_python(const std::string &msg);
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/export.cpp b/taichi/python/export.cpp
index 1cd8b7739f154..2cf3183a1f08d 100644
--- a/taichi/python/export.cpp
+++ b/taichi/python/export.cpp
@@ -7,7 +7,7 @@
 #include "taichi/common/interface.h"
 #include "taichi/util/io.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 PYBIND11_MODULE(taichi_python, m) {
   m.doc() = "taichi_python";
@@ -23,4 +23,4 @@ PYBIND11_MODULE(taichi_python, m) {
   export_ggui(m);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/export.h b/taichi/python/export.h
index 436d02ab9ade9..2cf4c06eab413 100644
--- a/taichi/python/export.h
+++ b/taichi/python/export.h
@@ -21,7 +21,7 @@
 
 #include "taichi/common/core.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 namespace py = pybind11;
 
@@ -35,4 +35,4 @@ void export_visual(py::module &m);
 
 void export_ggui(py::module &m);
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/export_ggui.cpp b/taichi/python/export_ggui.cpp
index b68e60f67a3d6..3ac90201700d0 100644
--- a/taichi/python/export_ggui.cpp
+++ b/taichi/python/export_ggui.cpp
@@ -594,22 +594,22 @@ void export_ggui(py::module &m) {
 
 TI_UI_NAMESPACE_END
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void export_ggui(py::module &m) {
   ui::export_ggui(m);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 #else
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void export_ggui(py::module &m) {
   m.attr("GGUI_AVAILABLE") = py::bool_(false);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 #endif
diff --git a/taichi/python/export_lang.cpp b/taichi/python/export_lang.cpp
index 0c70a7170b1e8..ec2469cc0ed78 100644
--- a/taichi/python/export_lang.cpp
+++ b/taichi/python/export_lang.cpp
@@ -36,12 +36,12 @@
 #include "taichi/rhi/cuda/cuda_context.h"
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 bool test_threading();
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 Expr expr_index(const Expr &expr, const Expr &index) {
   return expr[index];
@@ -49,9 +49,9 @@ Expr expr_index(const Expr &expr, const Expr &index) {
 
 std::string libdevice_path();
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 void export_lang(py::module &m) {
   using namespace taichi::lang;
   using namespace std::placeholders;
@@ -1360,4 +1360,4 @@ void export_lang(py::module &m) {
   });
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/export_math.cpp b/taichi/python/export_math.cpp
index 79dcbd215acc1..dc7905f2843f7 100644
--- a/taichi/python/export_math.cpp
+++ b/taichi/python/export_math.cpp
@@ -6,7 +6,7 @@
 #include "taichi/python/export.h"
 #include "taichi/common/dict.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 template <typename T>
 constexpr std::string get_type_short_name();
@@ -161,4 +161,4 @@ void export_math(py::module &m) {
   VectorRegistration<Vector4i>::run(m);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/export_visual.cpp b/taichi/python/export_visual.cpp
index 0c1534991c80b..4fa515b3431f0 100644
--- a/taichi/python/export_visual.cpp
+++ b/taichi/python/export_visual.cpp
@@ -7,7 +7,7 @@
 #include "taichi/util/image_io.h"
 #include "taichi/ui/gui/gui.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void export_visual(py::module &m) {
   // GUI
@@ -116,4 +116,4 @@ void export_visual(py::module &m) {
   });
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/memory_usage_monitor.cpp b/taichi/python/memory_usage_monitor.cpp
index c6d053d8ac194..e3eee9397894b 100644
--- a/taichi/python/memory_usage_monitor.cpp
+++ b/taichi/python/memory_usage_monitor.cpp
@@ -8,7 +8,7 @@
 #include "taichi/system/threading.h"
 #include "taichi/system/timer.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 namespace py = pybind11;
 using namespace py::literals;
@@ -116,4 +116,4 @@ class MemoryTest2 : public Task {
 TI_IMPLEMENTATION(Task, MemoryTest, "mem_test");
 TI_IMPLEMENTATION(Task, MemoryTest2, "mem_test2");
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/memory_usage_monitor.h b/taichi/python/memory_usage_monitor.h
index ac6cb5f2c2b73..254bc918211d2 100644
--- a/taichi/python/memory_usage_monitor.h
+++ b/taichi/python/memory_usage_monitor.h
@@ -2,7 +2,7 @@
 
 #include "taichi/system/virtual_memory.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class MemoryMonitor {
   // avoid including py::dict
@@ -21,4 +21,4 @@ void start_memory_monitoring(std::string output_fn,
                              int pid = -1,
                              real interval = 1);
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/python/snode_registry.cpp b/taichi/python/snode_registry.cpp
index a71eb92c4852b..7d1d2e605823f 100644
--- a/taichi/python/snode_registry.cpp
+++ b/taichi/python/snode_registry.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/snode.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 SNode *SNodeRegistry::create_root(Program *prog) {
   TI_ASSERT(prog != nullptr);
@@ -28,5 +27,4 @@ std::unique_ptr<SNode> SNodeRegistry::finalize(const SNode *snode) {
   return nullptr;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/python/snode_registry.h b/taichi/python/snode_registry.h
index 869e146899c27..dd31638d651e0 100644
--- a/taichi/python/snode_registry.h
+++ b/taichi/python/snode_registry.h
@@ -3,8 +3,7 @@
 #include <vector>
 #include <memory>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class SNode;
 class Program;
@@ -40,5 +39,4 @@ class SNodeRegistry {
   std::vector<std::unique_ptr<SNode>> snodes_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cpu/cpu_device.cpp b/taichi/rhi/cpu/cpu_device.cpp
index c70229fcaeae6..c7ee01aef9f4d 100644
--- a/taichi/rhi/cpu/cpu_device.cpp
+++ b/taichi/rhi/cpu/cpu_device.cpp
@@ -1,7 +1,6 @@
 #include "taichi/rhi/cpu/cpu_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace cpu {
 
@@ -91,5 +90,4 @@ uint64 CpuDevice::fetch_result_uint64(int i, uint64 *result_buffer) {
 }
 
 }  // namespace cpu
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cpu/cpu_device.h b/taichi/rhi/cpu/cpu_device.h
index f39fb1afea3fd..cb2aed624c1c3 100644
--- a/taichi/rhi/cpu/cpu_device.h
+++ b/taichi/rhi/cpu/cpu_device.h
@@ -8,8 +8,7 @@
 #include "taichi/rhi/llvm/llvm_device.h"
 #include "taichi/system/virtual_memory.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cpu {
 
 class CpuResourceBinder : public ResourceBinder {
@@ -131,6 +130,4 @@ class CpuDevice : public LlvmDevice {
 
 }  // namespace cpu
 
-}  // namespace lang
-
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_caching_allocator.cpp b/taichi/rhi/cuda/cuda_caching_allocator.cpp
index 1d4eeb174a577..7f1fab4384edb 100644
--- a/taichi/rhi/cuda/cuda_caching_allocator.cpp
+++ b/taichi/rhi/cuda/cuda_caching_allocator.cpp
@@ -1,7 +1,6 @@
 #include "taichi/rhi/cuda/cuda_caching_allocator.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cuda {
 
 CudaCachingAllocator::CudaCachingAllocator(LlvmDevice *device)
@@ -36,5 +35,4 @@ void CudaCachingAllocator::release(size_t sz, uint64_t *ptr) {
 }
 
 }  // namespace cuda
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_caching_allocator.h b/taichi/rhi/cuda/cuda_caching_allocator.h
index 1235d49ab90ec..906b9b904235e 100644
--- a/taichi/rhi/cuda/cuda_caching_allocator.h
+++ b/taichi/rhi/cuda/cuda_caching_allocator.h
@@ -6,8 +6,7 @@
 #include <stdint.h>
 #include <map>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cuda {
 
 class CudaCachingAllocator {
@@ -23,5 +22,4 @@ class CudaCachingAllocator {
 };
 
 }  // namespace cuda
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_context.cpp b/taichi/rhi/cuda/cuda_context.cpp
index a7dcb5a9e883c..aee2c1aea0a19 100644
--- a/taichi/rhi/cuda/cuda_context.cpp
+++ b/taichi/rhi/cuda/cuda_context.cpp
@@ -11,7 +11,7 @@
 #include "taichi/rhi/cuda/cuda_profiler.h"
 #include "taichi/analysis/offline_cache_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 CUDAContext::CUDAContext()
     : profiler_(nullptr), driver_(CUDADriver::get_instance_without_context()) {
@@ -141,4 +141,4 @@ CUDAContext &CUDAContext::get_instance() {
   return *context;
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_context.h b/taichi/rhi/cuda/cuda_context.h
index d63d81f10ca66..239bbec5cc5a7 100644
--- a/taichi/rhi/cuda/cuda_context.h
+++ b/taichi/rhi/cuda/cuda_context.h
@@ -7,7 +7,7 @@
 #include "taichi/program/kernel_profiler.h"
 #include "taichi/rhi/cuda/cuda_driver.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Note:
 // It would be ideal to create a CUDA context per Taichi program, yet CUDA
@@ -103,4 +103,4 @@ class CUDAContext {
   static CUDAContext &get_instance();
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_device.cpp b/taichi/rhi/cuda/cuda_device.cpp
index ac0d2917d9d1b..2dfc97562297a 100644
--- a/taichi/rhi/cuda/cuda_device.cpp
+++ b/taichi/rhi/cuda/cuda_device.cpp
@@ -1,7 +1,6 @@
 #include "taichi/rhi/cuda/cuda_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace cuda {
 
@@ -124,5 +123,4 @@ uint64 CudaDevice::fetch_result_uint64(int i, uint64 *result_buffer) {
   return ret;
 }
 }  // namespace cuda
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_device.h b/taichi/rhi/cuda/cuda_device.h
index d691cf4635d84..4b768db88357c 100644
--- a/taichi/rhi/cuda/cuda_device.h
+++ b/taichi/rhi/cuda/cuda_device.h
@@ -8,8 +8,7 @@
 #include "taichi/rhi/cuda/cuda_context.h"
 #include "taichi/rhi/llvm/llvm_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cuda {
 
 class CudaResourceBinder : public ResourceBinder {
@@ -142,6 +141,4 @@ class CudaDevice : public LlvmDevice {
 
 }  // namespace cuda
 
-}  // namespace lang
-
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_driver.cpp b/taichi/rhi/cuda/cuda_driver.cpp
index f266801d00a9b..1a3e59df25a37 100644
--- a/taichi/rhi/cuda/cuda_driver.cpp
+++ b/taichi/rhi/cuda/cuda_driver.cpp
@@ -4,7 +4,7 @@
 #include "taichi/rhi/cuda/cuda_context.h"
 #include "taichi/util/environ_config.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 std::string get_cuda_error_message(uint32 err) {
   const char *err_name_ptr;
@@ -132,4 +132,4 @@ bool CUSOLVERDriver::load_cusolver() {
 #undef PER_CUSOLVER_FUNCTION
   return cusolver_loaded_;
 }
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_driver.h b/taichi/rhi/cuda/cuda_driver.h
index 13fdf03480e50..77e725bf8ad5a 100644
--- a/taichi/rhi/cuda/cuda_driver.h
+++ b/taichi/rhi/cuda/cuda_driver.h
@@ -20,7 +20,7 @@ static_assert(sizeof(CUjit_option) == sizeof(uint32));
 }  // namespace taichi
 #endif
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Driver constants from cuda.h
 
@@ -178,4 +178,4 @@ class CUSOLVERDriver : protected CUDADriverBase {
   bool cusolver_loaded_{false};
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_profiler.cpp b/taichi/rhi/cuda/cuda_profiler.cpp
index 050d0eb8170e4..5bd11c2e0762f 100644
--- a/taichi/rhi/cuda/cuda_profiler.cpp
+++ b/taichi/rhi/cuda/cuda_profiler.cpp
@@ -3,7 +3,7 @@
 #include "taichi/rhi/cuda/cuda_driver.h"
 #include "taichi/rhi/cuda/cuda_context.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 #if defined(TI_WITH_CUDA)
 
@@ -369,4 +369,4 @@ void EventToolkit::update_timeline(
 }
 #endif
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cuda_profiler.h b/taichi/rhi/cuda/cuda_profiler.h
index 883a99cf9a50d..9c385664d62cc 100644
--- a/taichi/rhi/cuda/cuda_profiler.h
+++ b/taichi/rhi/cuda/cuda_profiler.h
@@ -9,7 +9,7 @@
 #include <string>
 #include <stdint.h>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 enum class ProfilingToolkit : int {
   undef,
@@ -95,4 +95,4 @@ class EventToolkit {
   }
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cupti_toolkit.cpp b/taichi/rhi/cuda/cupti_toolkit.cpp
index e5ba1a3c358be..e144772c6640f 100644
--- a/taichi/rhi/cuda/cupti_toolkit.cpp
+++ b/taichi/rhi/cuda/cupti_toolkit.cpp
@@ -12,7 +12,7 @@
 #include <nvperf_target.h>
 #endif
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Make sure these metrics can be captured in one pass (no kernel replay)
 // Metrics for calculating the kernel elapsed time are collected by default.
@@ -1130,4 +1130,4 @@ bool CuptiToolkit::update_record(
 }
 #endif
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/cuda/cupti_toolkit.h b/taichi/rhi/cuda/cupti_toolkit.h
index 98a5c3309730f..e62d9f4b97399 100644
--- a/taichi/rhi/cuda/cupti_toolkit.h
+++ b/taichi/rhi/cuda/cupti_toolkit.h
@@ -2,7 +2,7 @@
 
 #include "taichi/program/kernel_profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 struct CuptiConfig {
 #if defined(TI_WITH_CUDA_TOOLKIT)
@@ -43,4 +43,4 @@ class CuptiToolkit {
   CuptiImage cupti_image_;
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/rhi/device.cpp b/taichi/rhi/device.cpp
index 1d3af12cd8022..334364ad48de3 100644
--- a/taichi/rhi/device.cpp
+++ b/taichi/rhi/device.cpp
@@ -12,8 +12,7 @@
 #endif  // TI_WITH_CUDA
 #endif  // TI_WITH_VULKAN
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // FIXME: (penguinliong) We might have to differentiate buffer formats and
 // texture formats at some point because formats like `rgb10a2` are not easily
@@ -337,5 +336,4 @@ void GraphicsDevice::image_to_buffer(DevicePtr dst_buf,
   stream->submit_synced(cmd_list.get());
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/device.h b/taichi/rhi/device.h
index 46576da09f2aa..727ab1fa433e2 100644
--- a/taichi/rhi/device.h
+++ b/taichi/rhi/device.h
@@ -6,8 +6,7 @@
 #include <string>
 #include <vector>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 constexpr size_t kBufferSizeEntireSize = size_t(-1);
 
@@ -626,5 +625,4 @@ class TI_DLL_EXPORT GraphicsDevice : public Device {
                                const BufferImageCopyParams &params);
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/dx/dx_api.cpp b/taichi/rhi/dx/dx_api.cpp
index c9fe4be3a494a..3685639b9962b 100644
--- a/taichi/rhi/dx/dx_api.cpp
+++ b/taichi/rhi/dx/dx_api.cpp
@@ -1,8 +1,7 @@
 #include "taichi/rhi/dx/dx_api.h"
 #include "taichi/rhi/dx/dx_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 bool is_dx_api_available() {
@@ -18,5 +17,4 @@ std::shared_ptr<Device> make_dx11_device() {
 }
 
 }  // namespace directx11
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/dx/dx_api.h b/taichi/rhi/dx/dx_api.h
index fea81c475fe10..e4b4e2e7f56a2 100644
--- a/taichi/rhi/dx/dx_api.h
+++ b/taichi/rhi/dx/dx_api.h
@@ -9,8 +9,7 @@
 #include <d3d11.h>
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 bool is_dx_api_available();
@@ -18,5 +17,4 @@ bool is_dx_api_available();
 std::shared_ptr<Device> make_dx11_device();
 
 }  // namespace directx11
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/dx/dx_device.cpp b/taichi/rhi/dx/dx_device.cpp
index a69e503d551da..895b486b2d633 100644
--- a/taichi/rhi/dx/dx_device.cpp
+++ b/taichi/rhi/dx/dx_device.cpp
@@ -5,8 +5,7 @@
 #include "spirv_hlsl.hpp"
 #include <d3dcompiler.h>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 #ifdef TAICHI_DX11_DEBUG_WINDOW
@@ -952,7 +951,6 @@ ResourceBinder *Dx11Pipeline::resource_binder() {
 }
 
 }  // namespace directx11
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif
diff --git a/taichi/rhi/dx/dx_device.h b/taichi/rhi/dx/dx_device.h
index b0d1f863a6c41..ea8ccbf14df3a 100644
--- a/taichi/rhi/dx/dx_device.h
+++ b/taichi/rhi/dx/dx_device.h
@@ -6,8 +6,7 @@
 #include "taichi/rhi/dx/dx_info_queue.h"
 #include <d3d11.h>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 // Only enable debug layer when the corresponding testing facility is enabled
@@ -297,7 +296,6 @@ class Dx11Device : public GraphicsDevice {
 };
 
 }  // namespace directx11
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif
diff --git a/taichi/rhi/dx/dx_info_queue.cpp b/taichi/rhi/dx/dx_info_queue.cpp
index f852e44de15c8..ab8deb42f5027 100644
--- a/taichi/rhi/dx/dx_info_queue.cpp
+++ b/taichi/rhi/dx/dx_info_queue.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/rhi/dx/dx_info_queue.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 void check_dx_error(HRESULT hr, const char *msg);
@@ -138,7 +137,6 @@ int Dx11InfoQueue::live_object_count() {
 }
 
 }  // namespace directx11
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif
diff --git a/taichi/rhi/dx/dx_info_queue.h b/taichi/rhi/dx/dx_info_queue.h
index a98e8a6d958a5..0d74152d286de 100644
--- a/taichi/rhi/dx/dx_info_queue.h
+++ b/taichi/rhi/dx/dx_info_queue.h
@@ -5,8 +5,7 @@
 #include "taichi/rhi/device.h"
 #include <d3d11.h>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 class Dx11InfoQueue {
@@ -34,7 +33,6 @@ class Dx11InfoQueue {
 };
 
 }  // namespace directx11
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif
diff --git a/taichi/rhi/dx12/dx12_api.cpp b/taichi/rhi/dx12/dx12_api.cpp
index fbff2c4d18a6e..97e3ba958ccd8 100644
--- a/taichi/rhi/dx12/dx12_api.cpp
+++ b/taichi/rhi/dx12/dx12_api.cpp
@@ -1,7 +1,6 @@
 #include "taichi/rhi/dx12/dx12_api.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx12 {
 
 bool is_dx12_api_available() {
@@ -24,5 +23,4 @@ std::vector<uint8_t> validate_and_sign(
 }
 
 }  // namespace directx12
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/dx12/dx12_api.h b/taichi/rhi/dx12/dx12_api.h
index 485ddacb087f7..1bc0f43265acb 100644
--- a/taichi/rhi/dx12/dx12_api.h
+++ b/taichi/rhi/dx12/dx12_api.h
@@ -6,8 +6,7 @@
 
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx12 {
 
 bool is_dx12_api_available();
@@ -18,5 +17,4 @@ std::vector<uint8_t> validate_and_sign(
     std::vector<uint8_t> &input_dxil_container);
 
 }  // namespace directx12
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/interop/vulkan_cpu_interop.cpp b/taichi/rhi/interop/vulkan_cpu_interop.cpp
index 598e833977eee..f92c837c69118 100644
--- a/taichi/rhi/interop/vulkan_cpu_interop.cpp
+++ b/taichi/rhi/interop/vulkan_cpu_interop.cpp
@@ -7,8 +7,7 @@
 
 #include <unordered_map>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 #if TI_WITH_VULKAN && defined(TI_WITH_LLVM)
 
@@ -67,5 +66,4 @@ void memcpy_cpu_to_vulkan_via_staging(DevicePtr dst,
 }
 #endif  // TI_WITH_VULKAN
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/interop/vulkan_cpu_interop.h b/taichi/rhi/interop/vulkan_cpu_interop.h
index 4042ceca80be9..a975fad78092a 100644
--- a/taichi/rhi/interop/vulkan_cpu_interop.h
+++ b/taichi/rhi/interop/vulkan_cpu_interop.h
@@ -2,8 +2,7 @@
 
 #include "taichi/rhi/device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 void memcpy_cpu_to_vulkan(DevicePtr dst, DevicePtr src, uint64_t size);
 
@@ -12,5 +11,4 @@ void memcpy_cpu_to_vulkan_via_staging(DevicePtr dst,
                                       DevicePtr src,
                                       uint64_t size);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/interop/vulkan_cuda_interop.cpp b/taichi/rhi/interop/vulkan_cuda_interop.cpp
index bfa40da4a37a4..8e015fb516c24 100644
--- a/taichi/rhi/interop/vulkan_cuda_interop.cpp
+++ b/taichi/rhi/interop/vulkan_cuda_interop.cpp
@@ -9,8 +9,7 @@
 
 #include <unordered_map>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 #if TI_WITH_VULKAN && TI_WITH_CUDA
 
@@ -228,5 +227,4 @@ void memcpy_vulkan_to_cuda(DevicePtr dst, DevicePtr src, uint64_t size) {
 }
 #endif  // TI_WITH_VULKAN && TI_WITH_CUDA
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/interop/vulkan_cuda_interop.h b/taichi/rhi/interop/vulkan_cuda_interop.h
index 22bc32b68a401..dac441644572e 100644
--- a/taichi/rhi/interop/vulkan_cuda_interop.h
+++ b/taichi/rhi/interop/vulkan_cuda_interop.h
@@ -2,12 +2,10 @@
 
 #include "taichi/rhi/device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 void memcpy_cuda_to_vulkan(DevicePtr dst, DevicePtr src, uint64_t size);
 
 void memcpy_vulkan_to_cuda(DevicePtr dst, DevicePtr src, uint64_t size);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/llvm/llvm_device.cpp b/taichi/rhi/llvm/llvm_device.cpp
index 21b122b4b0a8c..a115f42e9c77e 100644
--- a/taichi/rhi/llvm/llvm_device.cpp
+++ b/taichi/rhi/llvm/llvm_device.cpp
@@ -1,7 +1,6 @@
 #include "taichi/rhi/llvm/llvm_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 uint64_t *LlvmDevice::allocate_llvm_runtime_memory_jit(
     const LlvmRuntimeAllocParams &params) {
@@ -12,5 +11,4 @@ uint64_t *LlvmDevice::allocate_llvm_runtime_memory_jit(
       taichi_result_buffer_runtime_query_id, params.result_buffer));
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/llvm/llvm_device.h b/taichi/rhi/llvm/llvm_device.h
index c8ea58ed2a001..1b27b660f71a9 100644
--- a/taichi/rhi/llvm/llvm_device.h
+++ b/taichi/rhi/llvm/llvm_device.h
@@ -2,8 +2,7 @@
 
 #include "taichi/rhi/device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class LlvmDevice : public Device {
  public:
@@ -23,5 +22,4 @@ class LlvmDevice : public Device {
       const LlvmRuntimeAllocParams &params);
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/metal/constants.h b/taichi/rhi/metal/constants.h
index 9894a3c2b8196..72ac15e5385d0 100644
--- a/taichi/rhi/metal/constants.h
+++ b/taichi/rhi/metal/constants.h
@@ -4,8 +4,7 @@
 
 #include "taichi/inc/constants.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 inline constexpr int kMaxNumThreadsGridStrideLoop = 64 * 1024;
@@ -14,5 +13,4 @@ inline constexpr int kMslVersionNone = 0;
 inline constexpr int kMaxNumSNodes = taichi_max_num_snodes;
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/metal/device.cpp b/taichi/rhi/metal/device.cpp
index d683648cc1f08..a201c1ae21b93 100644
--- a/taichi/rhi/metal/device.cpp
+++ b/taichi/rhi/metal/device.cpp
@@ -5,8 +5,7 @@
 #include "taichi/rhi/metal/constants.h"
 #include "taichi/runtime/metal/runtime_utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 #ifdef TI_PLATFORM_OSX
@@ -422,5 +421,4 @@ MakeDeviceResult make_compute_device(const ComputeDeviceParams &params) {
 #endif  // TI_PLATFORM_OSX
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/metal/device.h b/taichi/rhi/metal/device.h
index 5685c141393c9..4c572e9403bcd 100644
--- a/taichi/rhi/metal/device.h
+++ b/taichi/rhi/metal/device.h
@@ -6,8 +6,7 @@
 #include "taichi/runtime/metal/api.h"
 #include "taichi/runtime/metal/runtime_utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class MemoryPool;
 
@@ -48,5 +47,4 @@ struct MakeDeviceResult {
 MakeDeviceResult make_compute_device(const ComputeDeviceParams &params);
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/opengl/opengl_api.cpp b/taichi/rhi/opengl/opengl_api.cpp
index 4b82d6c368e08..326e5e81e0208 100644
--- a/taichi/rhi/opengl/opengl_api.cpp
+++ b/taichi/rhi/opengl/opengl_api.cpp
@@ -7,8 +7,7 @@
 #include "GLFW/glfw3.h"
 #include "taichi/rhi/opengl/opengl_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace opengl {
 
 #define PER_OPENGL_EXTENSION(x) bool opengl_extension_##x;
@@ -218,5 +217,4 @@ std::shared_ptr<Device> make_opengl_device() {
 }
 
 }  // namespace opengl
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/opengl/opengl_api.h b/taichi/rhi/opengl/opengl_api.h
index 5dda638ac87a1..e13919343f3e6 100644
--- a/taichi/rhi/opengl/opengl_api.h
+++ b/taichi/rhi/opengl/opengl_api.h
@@ -3,8 +3,7 @@
 #include "taichi/common/core.h"
 #include "taichi/rhi/device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace opengl {
 
 bool initialize_opengl(bool use_gles = false, bool error_tolerance = false);
@@ -18,5 +17,4 @@ std::shared_ptr<Device> make_opengl_device();
 #undef PER_OPENGL_EXTENSION
 
 }  // namespace opengl
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/opengl/opengl_device.cpp b/taichi/rhi/opengl/opengl_device.cpp
index 6f47ef2b01a94..9c78bf96110b9 100644
--- a/taichi/rhi/opengl/opengl_device.cpp
+++ b/taichi/rhi/opengl/opengl_device.cpp
@@ -3,8 +3,7 @@
 
 #include "spirv_glsl.hpp"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace opengl {
 
 namespace {
@@ -886,5 +885,4 @@ void GLCommandList::CmdImageToBuffer::execute() {
 }
 
 }  // namespace opengl
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/opengl/opengl_device.h b/taichi/rhi/opengl/opengl_device.h
index 54b9e6bf8ae83..4d1ae1a1698b0 100644
--- a/taichi/rhi/opengl/opengl_device.h
+++ b/taichi/rhi/opengl/opengl_device.h
@@ -5,8 +5,7 @@
 #include "glad/gl.h"
 #include "GLFW/glfw3.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace opengl {
 
 class GLDevice;
@@ -320,5 +319,4 @@ class GLSurface : public Surface {
 };
 
 }  // namespace opengl
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_common.h b/taichi/rhi/vulkan/vulkan_common.h
index 5ddf593bc8659..90cc6f393ef24 100644
--- a/taichi/rhi/vulkan/vulkan_common.h
+++ b/taichi/rhi/vulkan/vulkan_common.h
@@ -16,8 +16,7 @@
 
 #include <stdexcept>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 #define BAIL_ON_VK_BAD_RESULT(result, msg)               \
@@ -30,5 +29,4 @@ namespace vulkan {
 inline constexpr VkAllocationCallbacks *kNoVkAllocCallbacks = nullptr;
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_device.cpp b/taichi/rhi/vulkan/vulkan_device.cpp
index a110bac8d2a6e..efe78cb4d433d 100644
--- a/taichi/rhi/vulkan/vulkan_device.cpp
+++ b/taichi/rhi/vulkan/vulkan_device.cpp
@@ -17,8 +17,7 @@
 
 #include "spirv_reflect.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 const std::unordered_map<BufferFormat, VkFormat> buffer_format_ti_2_vk = {
@@ -2670,5 +2669,4 @@ VulkanStream::~VulkanStream() {
 }
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_device.h b/taichi/rhi/vulkan/vulkan_device.h
index 3c760075589e6..cd59877dfb23a 100644
--- a/taichi/rhi/vulkan/vulkan_device.h
+++ b/taichi/rhi/vulkan/vulkan_device.h
@@ -17,8 +17,7 @@
 #include <taichi/rhi/vulkan/vulkan_utils.h>
 #include <taichi/common/ref_counted_pool.h>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 using std::unordered_map;
@@ -740,5 +739,4 @@ VkFormat buffer_format_ti_to_vk(BufferFormat f);
 BufferFormat buffer_format_vk_to_ti(VkFormat f);
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_device_creator.cpp b/taichi/rhi/vulkan/vulkan_device_creator.cpp
index 6f476b1a24ea7..081be938d9d79 100644
--- a/taichi/rhi/vulkan/vulkan_device_creator.cpp
+++ b/taichi/rhi/vulkan/vulkan_device_creator.cpp
@@ -11,8 +11,7 @@
 #include "taichi/rhi/vulkan/vulkan_device.h"
 #include "taichi/common/logging.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 namespace {
@@ -776,5 +775,4 @@ void VulkanDeviceCreator::create_logical_device(bool manual_create) {
 }
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_device_creator.h b/taichi/rhi/vulkan/vulkan_device_creator.h
index 1574a35875562..6f744d8cb6cff 100644
--- a/taichi/rhi/vulkan/vulkan_device_creator.h
+++ b/taichi/rhi/vulkan/vulkan_device_creator.h
@@ -14,8 +14,7 @@
 #include <string>
 #include <functional>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 class VulkanDevice;
@@ -99,5 +98,4 @@ class TI_DLL_EXPORT VulkanDeviceCreator {
 };
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_loader.cpp b/taichi/rhi/vulkan/vulkan_loader.cpp
index 220a04e16081c..e7a810d64af30 100644
--- a/taichi/rhi/vulkan/vulkan_loader.cpp
+++ b/taichi/rhi/vulkan/vulkan_loader.cpp
@@ -8,8 +8,7 @@
 #include "GLFW/glfw3.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 VulkanLoader::VulkanLoader() {
@@ -142,5 +141,4 @@ void set_vulkan_visible_device(std::string id) {
 }
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_loader.h b/taichi/rhi/vulkan/vulkan_loader.h
index 32467912bc9ca..f5589dd679f3a 100644
--- a/taichi/rhi/vulkan/vulkan_loader.h
+++ b/taichi/rhi/vulkan/vulkan_loader.h
@@ -6,8 +6,7 @@
 #include "taichi/rhi/vulkan/vulkan_common.h"
 #include "taichi/system/dynamic_loader.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 class TI_DLL_EXPORT VulkanLoader {
@@ -51,5 +50,4 @@ TI_DLL_EXPORT bool is_vulkan_api_available();
 TI_DLL_EXPORT void set_vulkan_visible_device(std::string id);
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/rhi/vulkan/vulkan_utils.h b/taichi/rhi/vulkan/vulkan_utils.h
index 6c40fad48722d..721cad84630e1 100644
--- a/taichi/rhi/vulkan/vulkan_utils.h
+++ b/taichi/rhi/vulkan/vulkan_utils.h
@@ -15,8 +15,7 @@
 #include <string>
 #include <vector>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace vulkan {
 
 class VulkanEnvSettings {
@@ -101,5 +100,4 @@ inline WindowsSecurityAttributes::~WindowsSecurityAttributes() {
 #endif  //_WIN64
 
 }  // namespace vulkan
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cpu/aot_module_builder_impl.cpp b/taichi/runtime/cpu/aot_module_builder_impl.cpp
index b2c81c71792a5..18ddf76575538 100644
--- a/taichi/runtime/cpu/aot_module_builder_impl.cpp
+++ b/taichi/runtime/cpu/aot_module_builder_impl.cpp
@@ -5,8 +5,7 @@
 #include "taichi/codegen/cpu/codegen_cpu.h"
 #include "taichi/runtime/llvm/launch_arg_info.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cpu {
 
 LLVMCompiledKernel AotModuleBuilderImpl::compile_kernel(Kernel *kernel) {
@@ -15,5 +14,4 @@ LLVMCompiledKernel AotModuleBuilderImpl::compile_kernel(Kernel *kernel) {
 }
 
 }  // namespace cpu
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cpu/aot_module_builder_impl.h b/taichi/runtime/cpu/aot_module_builder_impl.h
index 9bf2d3a30136b..c324a3a714914 100644
--- a/taichi/runtime/cpu/aot_module_builder_impl.h
+++ b/taichi/runtime/cpu/aot_module_builder_impl.h
@@ -4,8 +4,7 @@
 #include "taichi/runtime/llvm/llvm_offline_cache.h"
 #include "taichi/runtime/llvm/llvm_aot_module_builder.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cpu {
 
 class AotModuleBuilderImpl : public LlvmAotModuleBuilder {
@@ -19,5 +18,4 @@ class AotModuleBuilderImpl : public LlvmAotModuleBuilder {
 };
 
 }  // namespace cpu
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cpu/aot_module_loader_impl.cpp b/taichi/runtime/cpu/aot_module_loader_impl.cpp
index bfe63e4370fa8..f802b3d64eb3a 100644
--- a/taichi/runtime/cpu/aot_module_loader_impl.cpp
+++ b/taichi/runtime/cpu/aot_module_loader_impl.cpp
@@ -5,8 +5,7 @@
 #include "taichi/runtime/llvm/llvm_runtime_executor.h"
 #include "taichi/codegen/cpu/codegen_cpu.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 class AotModuleImpl : public LlvmAotModule {
@@ -46,5 +45,4 @@ std::unique_ptr<aot::Module> make_aot_module(std::any mod_params) {
 }
 
 }  // namespace cpu
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cpu/aot_module_loader_impl.h b/taichi/runtime/cpu/aot_module_loader_impl.h
index f27fc7cf9d26a..45378c37edc61 100644
--- a/taichi/runtime/cpu/aot_module_loader_impl.h
+++ b/taichi/runtime/cpu/aot_module_loader_impl.h
@@ -2,8 +2,7 @@
 
 #include "taichi/aot/module_loader.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class LlvmRuntimeExecutor;
 
@@ -17,5 +16,4 @@ struct TI_DLL_EXPORT AotModuleParams {
 TI_DLL_EXPORT std::unique_ptr<aot::Module> make_aot_module(std::any mod_params);
 
 }  // namespace cpu
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cpu/jit_cpu.cpp b/taichi/runtime/cpu/jit_cpu.cpp
index b41c9041cb563..578d50c620283 100644
--- a/taichi/runtime/cpu/jit_cpu.cpp
+++ b/taichi/runtime/cpu/jit_cpu.cpp
@@ -49,7 +49,7 @@
 #include "taichi/util/file_sequence_writer.h"
 #include "taichi/runtime/llvm/llvm_context.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 #ifdef TI_WITH_LLVM
 using namespace llvm;
@@ -361,4 +361,4 @@ std::unique_ptr<JITSession> create_llvm_jit_session_cpu(
 #endif
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cuda/aot_module_builder_impl.cpp b/taichi/runtime/cuda/aot_module_builder_impl.cpp
index 6669f899745be..e9a8072bfb1b8 100644
--- a/taichi/runtime/cuda/aot_module_builder_impl.cpp
+++ b/taichi/runtime/cuda/aot_module_builder_impl.cpp
@@ -5,8 +5,7 @@
 #include "taichi/codegen/cuda/codegen_cuda.h"
 #include "taichi/runtime/llvm/launch_arg_info.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cuda {
 
 LLVMCompiledKernel AotModuleBuilderImpl::compile_kernel(Kernel *kernel) {
@@ -15,5 +14,4 @@ LLVMCompiledKernel AotModuleBuilderImpl::compile_kernel(Kernel *kernel) {
 }
 
 }  // namespace cuda
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cuda/aot_module_builder_impl.h b/taichi/runtime/cuda/aot_module_builder_impl.h
index 278c403b0d7d5..9a449176bebb6 100644
--- a/taichi/runtime/cuda/aot_module_builder_impl.h
+++ b/taichi/runtime/cuda/aot_module_builder_impl.h
@@ -4,8 +4,7 @@
 #include "taichi/runtime/llvm/llvm_offline_cache.h"
 #include "taichi/runtime/llvm/llvm_aot_module_builder.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace cuda {
 
 class AotModuleBuilderImpl : public LlvmAotModuleBuilder {
@@ -19,5 +18,4 @@ class AotModuleBuilderImpl : public LlvmAotModuleBuilder {
 };
 
 }  // namespace cuda
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cuda/aot_module_loader_impl.cpp b/taichi/runtime/cuda/aot_module_loader_impl.cpp
index 1c0a9285cf762..1b13d21e6d8e9 100644
--- a/taichi/runtime/cuda/aot_module_loader_impl.cpp
+++ b/taichi/runtime/cuda/aot_module_loader_impl.cpp
@@ -5,8 +5,7 @@
 #include "taichi/runtime/llvm/llvm_runtime_executor.h"
 #include "taichi/codegen/cuda/codegen_cuda.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 class AotModuleImpl : public LlvmAotModule {
@@ -46,5 +45,4 @@ std::unique_ptr<aot::Module> make_aot_module(std::any mod_params) {
 }
 
 }  // namespace cuda
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cuda/aot_module_loader_impl.h b/taichi/runtime/cuda/aot_module_loader_impl.h
index 3bd0040d5ebc9..e2d9bc79a0a5e 100644
--- a/taichi/runtime/cuda/aot_module_loader_impl.h
+++ b/taichi/runtime/cuda/aot_module_loader_impl.h
@@ -2,8 +2,7 @@
 
 #include "taichi/aot/module_loader.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class LlvmRuntimeExecutor;
 
@@ -17,5 +16,4 @@ struct TI_DLL_EXPORT AotModuleParams {
 TI_DLL_EXPORT std::unique_ptr<aot::Module> make_aot_module(std::any mod_params);
 
 }  // namespace cuda
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cuda/jit_cuda.cpp b/taichi/runtime/cuda/jit_cuda.cpp
index 7f84619a979c5..46f47695a7f93 100644
--- a/taichi/runtime/cuda/jit_cuda.cpp
+++ b/taichi/runtime/cuda/jit_cuda.cpp
@@ -1,7 +1,7 @@
 #include "taichi/runtime/cuda/jit_cuda.h"
 #include "taichi/runtime/llvm/llvm_context.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 #if defined(TI_WITH_CUDA)
 
@@ -258,4 +258,4 @@ std::unique_ptr<JITSession> create_llvm_jit_session_cuda(
 }
 #endif
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cuda/jit_cuda.h b/taichi/runtime/cuda/jit_cuda.h
index a207f4b58110a..183eb4d3f69ab 100644
--- a/taichi/runtime/cuda/jit_cuda.h
+++ b/taichi/runtime/cuda/jit_cuda.h
@@ -35,7 +35,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 #if defined(TI_WITH_CUDA)
 class JITModuleCUDA : public JITModule {
@@ -110,4 +110,4 @@ std::unique_ptr<JITSession> create_llvm_jit_session_cuda(
     CompileConfig *config,
     Arch arch);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/cuda/runtime.cpp b/taichi/runtime/cuda/runtime.cpp
index 70497202e2417..47365cf6a0374 100644
--- a/taichi/runtime/cuda/runtime.cpp
+++ b/taichi/runtime/cuda/runtime.cpp
@@ -1,7 +1,7 @@
 #include "taichi/runtime/runtime.h"
 #include "taichi/rhi/cuda/cuda_context.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 #if !defined(TI_WITH_CUDA)
 static_assert(
@@ -37,4 +37,4 @@ static class RuntimeCUDAInjector {
   }
 } injector;
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/dx12/aot_module_builder_impl.cpp b/taichi/runtime/dx12/aot_module_builder_impl.cpp
index 95f4ab97103b1..818df6ee354ba 100644
--- a/taichi/runtime/dx12/aot_module_builder_impl.cpp
+++ b/taichi/runtime/dx12/aot_module_builder_impl.cpp
@@ -6,8 +6,7 @@
 #include "taichi/runtime/llvm/launch_arg_info.h"
 #include "taichi/runtime/program_impls/llvm/llvm_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx12 {
 
 AotModuleBuilderImpl::AotModuleBuilderImpl(LlvmProgramImpl *prog) : prog(prog) {
@@ -47,5 +46,4 @@ void AotModuleBuilderImpl::dump(const std::string &output_dir,
 }
 
 }  // namespace directx12
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/dx12/aot_module_builder_impl.h b/taichi/runtime/dx12/aot_module_builder_impl.h
index e7993cd2c3c0a..6c903ad57da51 100644
--- a/taichi/runtime/dx12/aot_module_builder_impl.h
+++ b/taichi/runtime/dx12/aot_module_builder_impl.h
@@ -5,8 +5,7 @@
 #include "taichi/runtime/llvm/llvm_aot_module_builder.h"
 #include "taichi/aot/module_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx12 {
 
 struct ModuleDataDX12 : public aot::ModuleData {
@@ -42,5 +41,4 @@ class AotModuleBuilderImpl : public AotModuleBuilder {
 };
 
 }  // namespace directx12
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/aot_graph_data.h b/taichi/runtime/gfx/aot_graph_data.h
index b9d8b4315ab65..10372f996120c 100644
--- a/taichi/runtime/gfx/aot_graph_data.h
+++ b/taichi/runtime/gfx/aot_graph_data.h
@@ -1,8 +1,7 @@
 #pragma once
 #include "taichi/runtime/gfx/runtime.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 class KernelImpl : public aot::Kernel {
  public:
@@ -25,5 +24,4 @@ class KernelImpl : public aot::Kernel {
   const GfxRuntime::RegisterParams params_;
 };
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/aot_module_builder_impl.cpp b/taichi/runtime/gfx/aot_module_builder_impl.cpp
index 364a1657dfb91..d2bf803778a75 100644
--- a/taichi/runtime/gfx/aot_module_builder_impl.cpp
+++ b/taichi/runtime/gfx/aot_module_builder_impl.cpp
@@ -7,8 +7,7 @@
 #include "taichi/codegen/spirv/spirv_codegen.h"
 #include "taichi/runtime/gfx/aot_graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 namespace {
@@ -256,5 +255,4 @@ void AotModuleBuilderImpl::add_per_backend_tmpl(const std::string &identifier,
 }
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/aot_module_builder_impl.h b/taichi/runtime/gfx/aot_module_builder_impl.h
index 290bc72b6d9b1..86cc9340ba290 100644
--- a/taichi/runtime/gfx/aot_module_builder_impl.h
+++ b/taichi/runtime/gfx/aot_module_builder_impl.h
@@ -9,8 +9,7 @@
 #include "taichi/codegen/spirv/snode_struct_compiler.h"
 #include "taichi/codegen/spirv/kernel_utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 class AotModuleBuilderImpl : public AotModuleBuilder {
@@ -57,5 +56,4 @@ class AotModuleBuilderImpl : public AotModuleBuilder {
 };
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/aot_module_loader_impl.cpp b/taichi/runtime/gfx/aot_module_loader_impl.cpp
index 4ec285e69f055..689db753966ce 100644
--- a/taichi/runtime/gfx/aot_module_loader_impl.cpp
+++ b/taichi/runtime/gfx/aot_module_loader_impl.cpp
@@ -6,8 +6,7 @@
 #include "taichi/runtime/gfx/runtime.h"
 #include "taichi/aot/graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 namespace {
 class FieldImpl : public aot::Field {
@@ -195,5 +194,4 @@ std::unique_ptr<aot::Module> make_aot_module(std::any mod_params,
 }
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/aot_module_loader_impl.h b/taichi/runtime/gfx/aot_module_loader_impl.h
index 2a211a171b2de..2557d07a59913 100644
--- a/taichi/runtime/gfx/aot_module_loader_impl.h
+++ b/taichi/runtime/gfx/aot_module_loader_impl.h
@@ -12,8 +12,7 @@
 #include "taichi/aot/module_builder.h"
 #include "taichi/aot/module_loader.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 struct TI_DLL_EXPORT AotModuleParams {
@@ -33,5 +32,4 @@ TI_DLL_EXPORT std::unique_ptr<aot::Module> make_aot_module(
     Arch device_api_backend);
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/aot_utils.h b/taichi/runtime/gfx/aot_utils.h
index 2bfdc367f57f1..308f8de86e7ce 100644
--- a/taichi/runtime/gfx/aot_utils.h
+++ b/taichi/runtime/gfx/aot_utils.h
@@ -6,8 +6,7 @@
 #include "taichi/codegen/spirv/kernel_utils.h"
 #include "taichi/aot/module_loader.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 /**
@@ -25,5 +24,4 @@ struct TaichiAotData {
 };
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/runtime.cpp b/taichi/runtime/gfx/runtime.cpp
index f095ec3b21271..a7305214725fa 100644
--- a/taichi/runtime/gfx/runtime.cpp
+++ b/taichi/runtime/gfx/runtime.cpp
@@ -16,8 +16,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 namespace {
@@ -741,5 +740,4 @@ GfxRuntime::RegisterParams run_codegen(
 }
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/runtime.h b/taichi/runtime/gfx/runtime.h
index 9e9116fbc78b2..7afa88a3e3dfb 100644
--- a/taichi/runtime/gfx/runtime.h
+++ b/taichi/runtime/gfx/runtime.h
@@ -13,8 +13,7 @@
 #include "taichi/program/snode_expr_utils.h"
 #include "taichi/program/program_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 using namespace taichi::lang::spirv;
@@ -162,5 +161,4 @@ GfxRuntime::RegisterParams run_codegen(
     const std::vector<CompiledSNodeStructs> &compiled_structs);
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/snode_tree_manager.cpp b/taichi/runtime/gfx/snode_tree_manager.cpp
index 9c5697c18dcc9..e3f88de6818dc 100644
--- a/taichi/runtime/gfx/snode_tree_manager.cpp
+++ b/taichi/runtime/gfx/snode_tree_manager.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/runtime/gfx/runtime.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 SNodeTreeManager::SNodeTreeManager(GfxRuntime *rtm) : runtime_(rtm) {
@@ -52,5 +51,4 @@ DevicePtr SNodeTreeManager::get_snode_tree_device_ptr(int tree_id) {
 }
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/gfx/snode_tree_manager.h b/taichi/runtime/gfx/snode_tree_manager.h
index 99adefc2a8b85..43206a5f11210 100644
--- a/taichi/runtime/gfx/snode_tree_manager.h
+++ b/taichi/runtime/gfx/snode_tree_manager.h
@@ -6,8 +6,7 @@
 #include "taichi/codegen/spirv/snode_struct_compiler.h"
 #include "taichi/struct/snode_tree.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace gfx {
 
 class GfxRuntime;
@@ -41,5 +40,4 @@ class SNodeTreeManager {
 };
 
 }  // namespace gfx
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/aot_graph_data.h b/taichi/runtime/llvm/aot_graph_data.h
index b772adfed1ee0..007e05acde64b 100644
--- a/taichi/runtime/llvm/aot_graph_data.h
+++ b/taichi/runtime/llvm/aot_graph_data.h
@@ -3,8 +3,7 @@
 #include "taichi/aot/graph_data.h"
 #include "taichi/aot/module_loader.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace llvm_aot {
 
 class KernelImpl : public aot::Kernel {
@@ -47,5 +46,4 @@ class FieldImpl : public aot::Field {
 };
 
 }  // namespace llvm_aot
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/launch_arg_info.cpp b/taichi/runtime/llvm/launch_arg_info.cpp
index b44b4c4e4792d..1037d51ac9610 100644
--- a/taichi/runtime/llvm/launch_arg_info.cpp
+++ b/taichi/runtime/llvm/launch_arg_info.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/program/kernel.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 bool LlvmLaunchArgInfo::operator==(const LlvmLaunchArgInfo &other) const {
   return is_array == other.is_array;
@@ -18,5 +17,4 @@ std::vector<LlvmLaunchArgInfo> infer_launch_args(const Kernel *kernel) {
   return res;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/launch_arg_info.h b/taichi/runtime/llvm/launch_arg_info.h
index 1227c8b8f4911..b0d0130850770 100644
--- a/taichi/runtime/llvm/launch_arg_info.h
+++ b/taichi/runtime/llvm/launch_arg_info.h
@@ -5,8 +5,7 @@
 #include "taichi/common/core.h"
 #include "taichi/common/serialization.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // TODO: It would be better if this can be unified with Callable::Arg. However,
 // Callable::Arg is not easily serializable.
@@ -25,5 +24,4 @@ class Kernel;
 
 std::vector<LlvmLaunchArgInfo> infer_launch_args(const Kernel *kernel);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_aot_module_builder.cpp b/taichi/runtime/llvm/llvm_aot_module_builder.cpp
index c8e61c4484325..1eb9f4411edda 100644
--- a/taichi/runtime/llvm/llvm_aot_module_builder.cpp
+++ b/taichi/runtime/llvm/llvm_aot_module_builder.cpp
@@ -5,8 +5,7 @@
 #include "taichi/runtime/program_impls/llvm/llvm_program.h"
 #include "taichi/runtime/llvm/aot_graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 void LlvmAotModuleBuilder::dump(const std::string &output_dir,
                                 const std::string &filename) const {
@@ -74,5 +73,4 @@ void LlvmAotModuleBuilder::add_compiled_kernel(aot::Kernel *kernel) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_aot_module_builder.h b/taichi/runtime/llvm/llvm_aot_module_builder.h
index 2efa9b496b88f..6e6b313ce80c5 100644
--- a/taichi/runtime/llvm/llvm_aot_module_builder.h
+++ b/taichi/runtime/llvm/llvm_aot_module_builder.h
@@ -4,8 +4,7 @@
 #include "taichi/runtime/llvm/llvm_offline_cache.h"
 #include "taichi/codegen/llvm/codegen_llvm.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class LlvmAotModuleBuilder : public AotModuleBuilder {
  public:
@@ -38,5 +37,4 @@ class LlvmAotModuleBuilder : public AotModuleBuilder {
   LlvmProgramImpl *prog_ = nullptr;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_aot_module_loader.cpp b/taichi/runtime/llvm/llvm_aot_module_loader.cpp
index 028483c96e780..45cf8baf8922d 100644
--- a/taichi/runtime/llvm/llvm_aot_module_loader.cpp
+++ b/taichi/runtime/llvm/llvm_aot_module_loader.cpp
@@ -1,8 +1,7 @@
 #include "taichi/runtime/llvm/llvm_aot_module_loader.h"
 #include "taichi/runtime/llvm/aot_graph_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 LlvmOfflineCache::KernelCacheData LlvmAotModule::load_kernel_from_cache(
     const std::string &name) {
@@ -80,5 +79,4 @@ void allocate_aot_snode_tree_type(aot::Module *aot_module,
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_aot_module_loader.h b/taichi/runtime/llvm/llvm_aot_module_loader.h
index cbb1f0f1d40e6..ce8e36cda113c 100644
--- a/taichi/runtime/llvm/llvm_aot_module_loader.h
+++ b/taichi/runtime/llvm/llvm_aot_module_loader.h
@@ -3,8 +3,7 @@
 #include "taichi/aot/module_loader.h"
 #include "taichi/runtime/llvm/llvm_runtime_executor.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 /* TODO(zhanlue) refactor this interface once SNodeTreeType is available
    The "aot::Field" created by "make_new_field()" is a SNodeTree in essense.
@@ -82,5 +81,4 @@ class LlvmAotModule : public aot::Module {
   std::unordered_set<int> initialized_snode_tree_ids;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_context.cpp b/taichi/runtime/llvm/llvm_context.cpp
index 5689ff71ba513..0fda8cf179ce2 100644
--- a/taichi/runtime/llvm/llvm_context.cpp
+++ b/taichi/runtime/llvm/llvm_context.cpp
@@ -58,8 +58,7 @@
 #include "taichi/rhi/cuda/cuda_context.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 using namespace llvm;
 
@@ -1000,5 +999,4 @@ std::string TaichiLLVMContext::get_struct_for_func_name(int tls_size) {
 
 TI_REGISTER_TASK(make_slim_libdevice);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_context.h b/taichi/runtime/llvm/llvm_context.h
index 9735a18acf503..9ca2ddf4408e6 100644
--- a/taichi/runtime/llvm/llvm_context.h
+++ b/taichi/runtime/llvm/llvm_context.h
@@ -15,8 +15,7 @@
 #include "taichi/jit/jit_session.h"
 #include "taichi/codegen/llvm/llvm_compiled_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class JITSessionCPU;
 class LlvmProgramImpl;
@@ -205,5 +204,4 @@ std::unique_ptr<llvm::Module> module_from_bitcode_file(
     const std::string &bitcode_path,
     llvm::LLVMContext *ctx);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_offline_cache.cpp b/taichi/runtime/llvm/llvm_offline_cache.cpp
index 70d6bf853889f..f91a9567735ca 100644
--- a/taichi/runtime/llvm/llvm_offline_cache.cpp
+++ b/taichi/runtime/llvm/llvm_offline_cache.cpp
@@ -19,8 +19,7 @@
 #include "taichi/util/lock.h"
 #include "taichi/util/offline_cache.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 using Format = LlvmOfflineCache::Format;
@@ -400,5 +399,4 @@ LlvmOfflineCache::KernelCacheData LlvmOfflineCache::KernelCacheData::clone()
     const {
   return {kernel_key, args, compiled_data.clone()};
 }
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_offline_cache.h b/taichi/runtime/llvm/llvm_offline_cache.h
index 5142da03bb4a1..f99643a0052ef 100644
--- a/taichi/runtime/llvm/llvm_offline_cache.h
+++ b/taichi/runtime/llvm/llvm_offline_cache.h
@@ -11,8 +11,7 @@
 #include "taichi/util/offline_cache.h"
 #include "taichi/codegen/llvm/llvm_compiled_data.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 struct LlvmOfflineCache {
   using Version = uint16[3];  // {MAJOR, MINOR, PATCH}
@@ -178,6 +177,5 @@ class LlvmOfflineCacheFileWriter {
   bool mangled_{false};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 #endif  // TI_WITH_LLVM
diff --git a/taichi/runtime/llvm/llvm_runtime_executor.cpp b/taichi/runtime/llvm/llvm_runtime_executor.cpp
index 576b31ea21646..447ccb4270317 100644
--- a/taichi/runtime/llvm/llvm_runtime_executor.cpp
+++ b/taichi/runtime/llvm/llvm_runtime_executor.cpp
@@ -11,8 +11,7 @@
 #include "taichi/rhi/cuda/cuda_context.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 void assert_failed_host(const char *msg) {
   TI_ERROR("Assertion failure: {}", msg);
@@ -629,5 +628,4 @@ void LlvmRuntimeExecutor::prepare_runtime_context(RuntimeContext *ctx) {
   ctx->runtime = get_llvm_runtime();
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/llvm_runtime_executor.h b/taichi/runtime/llvm/llvm_runtime_executor.h
index 901f2b27154cf..85cc3def851e0 100644
--- a/taichi/runtime/llvm/llvm_runtime_executor.h
+++ b/taichi/runtime/llvm/llvm_runtime_executor.h
@@ -20,8 +20,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace cuda {
 class CudaDevice;
@@ -162,7 +161,6 @@ class LlvmRuntimeExecutor {
   friend SNodeTreeBufferManager;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif  // TI_WITH_LLVM
diff --git a/taichi/runtime/llvm/runtime_module/mem_request.h b/taichi/runtime/llvm/runtime_module/mem_request.h
index 0bfe567e4036b..9ebdce7c95f31 100644
--- a/taichi/runtime/llvm/runtime_module/mem_request.h
+++ b/taichi/runtime/llvm/runtime_module/mem_request.h
@@ -4,8 +4,7 @@
 #include "taichi/inc/constants.h"
 
 #if defined(TI_RUNTIME_HOST)
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 #endif
 
 struct MemRequest {
@@ -24,6 +23,5 @@ struct MemRequestQueue {
 };
 
 #if defined(TI_RUNTIME_HOST)
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 #endif
diff --git a/taichi/runtime/llvm/snode_tree_buffer_manager.cpp b/taichi/runtime/llvm/snode_tree_buffer_manager.cpp
index d0965b4681400..7b8a81e9ee266 100644
--- a/taichi/runtime/llvm/snode_tree_buffer_manager.cpp
+++ b/taichi/runtime/llvm/snode_tree_buffer_manager.cpp
@@ -1,7 +1,7 @@
 #include "snode_tree_buffer_manager.h"
 #include "taichi/runtime/llvm/llvm_runtime_executor.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 SNodeTreeBufferManager::SNodeTreeBufferManager(
     LlvmRuntimeExecutor *runtime_exec)
@@ -79,4 +79,4 @@ void SNodeTreeBufferManager::destroy(SNodeTree *snode_tree) {
   TI_DEBUG("SNode tree {} destroyed.", snode_tree_id);
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/llvm/snode_tree_buffer_manager.h b/taichi/runtime/llvm/snode_tree_buffer_manager.h
index 872d4cc0a8828..b5a6edb644349 100644
--- a/taichi/runtime/llvm/snode_tree_buffer_manager.h
+++ b/taichi/runtime/llvm/snode_tree_buffer_manager.h
@@ -7,7 +7,7 @@
 
 using Ptr = uint8_t *;
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class JITModule;
 class LlvmRuntimeExecutor;
@@ -35,4 +35,4 @@ class SNodeTreeBufferManager {
   std::size_t sizes_[kMaxNumSnodeTreesLlvm];
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/aot_module_builder_impl.cpp b/taichi/runtime/metal/aot_module_builder_impl.cpp
index 4abedfdcc5639..ffdcba25a3b44 100644
--- a/taichi/runtime/metal/aot_module_builder_impl.cpp
+++ b/taichi/runtime/metal/aot_module_builder_impl.cpp
@@ -4,8 +4,7 @@
 
 #include "taichi/codegen/metal/codegen_metal.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 AotModuleBuilderImpl::AotModuleBuilderImpl(
@@ -104,5 +103,4 @@ void AotModuleBuilderImpl::add_per_backend_tmpl(const std::string &identifier,
 }
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/aot_module_builder_impl.h b/taichi/runtime/metal/aot_module_builder_impl.h
index c62580edf176a..04846a0d3f211 100644
--- a/taichi/runtime/metal/aot_module_builder_impl.h
+++ b/taichi/runtime/metal/aot_module_builder_impl.h
@@ -8,8 +8,7 @@
 #include "taichi/runtime/metal/aot_utils.h"
 #include "taichi/codegen/metal/struct_metal.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 class AotModuleBuilderImpl : public AotModuleBuilder {
@@ -50,5 +49,4 @@ class AotModuleBuilderImpl : public AotModuleBuilder {
 };
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/aot_module_loader_impl.cpp b/taichi/runtime/metal/aot_module_loader_impl.cpp
index 540cddfecf4b2..4008f62399c52 100644
--- a/taichi/runtime/metal/aot_module_loader_impl.cpp
+++ b/taichi/runtime/metal/aot_module_loader_impl.cpp
@@ -3,8 +3,7 @@
 #include "taichi/runtime/metal/aot_utils.h"
 #include "taichi/runtime/metal/kernel_manager.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 namespace {
 
@@ -107,5 +106,4 @@ std::unique_ptr<aot::Module> make_aot_module(std::any mod_params) {
 }
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/aot_module_loader_impl.h b/taichi/runtime/metal/aot_module_loader_impl.h
index 04cc71f494f78..43ed12451c3f4 100644
--- a/taichi/runtime/metal/aot_module_loader_impl.h
+++ b/taichi/runtime/metal/aot_module_loader_impl.h
@@ -6,8 +6,7 @@
 
 #include "taichi/aot/module_loader.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 class KernelManager;
@@ -19,5 +18,4 @@ struct AotModuleParams {
 
 std::unique_ptr<aot::Module> make_aot_module(std::any mod_params);
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/aot_utils.h b/taichi/runtime/metal/aot_utils.h
index fdac85474aaa1..9ff52b6431f96 100644
--- a/taichi/runtime/metal/aot_utils.h
+++ b/taichi/runtime/metal/aot_utils.h
@@ -4,8 +4,7 @@
 
 #include "taichi/runtime/metal/kernel_utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 /**
@@ -21,5 +20,4 @@ struct TaichiAotData {
 };
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/api.cpp b/taichi/runtime/metal/api.cpp
index 3a21192cb0562..92236bfd0933d 100644
--- a/taichi/runtime/metal/api.cpp
+++ b/taichi/runtime/metal/api.cpp
@@ -3,8 +3,7 @@
 #include "taichi/rhi/metal/constants.h"
 #include "taichi/util/environ_config.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 #ifdef TI_PLATFORM_OSX
@@ -195,5 +194,4 @@ bool is_metal_api_available() {
 }
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/api.h b/taichi/runtime/metal/api.h
index 07e5c7f483d5c..a11af1cb4e36d 100644
--- a/taichi/runtime/metal/api.h
+++ b/taichi/runtime/metal/api.h
@@ -9,8 +9,7 @@
 #include "taichi/util/lang_util.h"
 #include "taichi/platform/mac/objc_api.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 // Expose these incomplete structs so that other modules (e.g. MetalRuntime)
@@ -169,5 +168,4 @@ size_t get_max_total_threads_per_threadgroup(
 bool is_metal_api_available();
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/data_types.cpp b/taichi/runtime/metal/data_types.cpp
index 5130f21c86a98..4f0c2f7201b5b 100644
--- a/taichi/runtime/metal/data_types.cpp
+++ b/taichi/runtime/metal/data_types.cpp
@@ -1,6 +1,6 @@
 #include "taichi/runtime/metal/data_types.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace metal {
 
 MetalDataType to_metal_type(DataType dt) {
@@ -135,4 +135,4 @@ std::string metal_unary_op_type_symbol(UnaryOpType type) {
 }
 
 }  // namespace metal
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/data_types.h b/taichi/runtime/metal/data_types.h
index d794058014067..da109fe0c4fa9 100644
--- a/taichi/runtime/metal/data_types.h
+++ b/taichi/runtime/metal/data_types.h
@@ -4,7 +4,7 @@
 
 #include "taichi/util/lang_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace metal {
 
 enum class MetalDataType : int {
@@ -46,4 +46,4 @@ inline bool is_metal_binary_op_infix(BinaryOpType type) {
 
 }  // namespace metal
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/features.h b/taichi/runtime/metal/features.h
index 475573e116ffb..81a8d13f549d4 100644
--- a/taichi/runtime/metal/features.h
+++ b/taichi/runtime/metal/features.h
@@ -4,7 +4,7 @@
 
 #include "taichi/util/lang_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 namespace metal {
 
 inline bool is_supported_sparse_type(SNodeType t) {
@@ -14,4 +14,4 @@ inline bool is_supported_sparse_type(SNodeType t) {
 
 }  // namespace metal
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/kernel_manager.cpp b/taichi/runtime/metal/kernel_manager.cpp
index 3b4cfa977308e..0ed8977afc806 100644
--- a/taichi/runtime/metal/kernel_manager.cpp
+++ b/taichi/runtime/metal/kernel_manager.cpp
@@ -31,8 +31,7 @@
 #include "taichi/program/program.h"
 #endif  // TI_PLATFORM_OSX
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 #ifdef TI_PLATFORM_OSX
@@ -1389,5 +1388,4 @@ DeviceAllocation KernelManager::allocate_memory(
 }
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/kernel_manager.h b/taichi/runtime/metal/kernel_manager.h
index 376b3a09d59c4..cde2c34befd87 100644
--- a/taichi/runtime/metal/kernel_manager.h
+++ b/taichi/runtime/metal/kernel_manager.h
@@ -13,8 +13,7 @@
 #include "taichi/program/kernel_profiler.h"
 #include "taichi/system/memory_pool.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Kernel;
 struct RuntimeContext;
@@ -83,5 +82,4 @@ class KernelManager {
 };
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/kernel_utils.cpp b/taichi/runtime/metal/kernel_utils.cpp
index 5f06725ca8858..6ee2ffc7c520c 100644
--- a/taichi/runtime/metal/kernel_utils.cpp
+++ b/taichi/runtime/metal/kernel_utils.cpp
@@ -7,8 +7,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace metal {
 
@@ -164,5 +163,4 @@ KernelContextAttributes::KernelContextAttributes(const Kernel &kernel)
 
 }  // namespace metal
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/kernel_utils.h b/taichi/runtime/metal/kernel_utils.h
index db565bf2bd84e..edb7f9c41ada4 100644
--- a/taichi/runtime/metal/kernel_utils.h
+++ b/taichi/runtime/metal/kernel_utils.h
@@ -16,8 +16,7 @@
 // compiled to more than one Metal compute kernels. Concretely, each offloaded
 // task in the Taichi kernel maps to a Metal kernel.
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Kernel;
 class SNode;
@@ -322,5 +321,4 @@ struct BufferMetaData {
 };
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/runtime_utils.cpp b/taichi/runtime/metal/runtime_utils.cpp
index be6c494478cfd..e92fd890a85cc 100644
--- a/taichi/runtime/metal/runtime_utils.cpp
+++ b/taichi/runtime/metal/runtime_utils.cpp
@@ -6,8 +6,7 @@
 #include "taichi/math/arithmetic.h"
 #include "taichi/system/memory_pool.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace metal {
 
 BufferMemoryView::BufferMemoryView(std::size_t size, MemoryPool *mem_pool) {
@@ -19,5 +18,4 @@ BufferMemoryView::BufferMemoryView(std::size_t size, MemoryPool *mem_pool) {
 }
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/metal/runtime_utils.h b/taichi/runtime/metal/runtime_utils.h
index ad5121b16b044..73606ce297c71 100644
--- a/taichi/runtime/metal/runtime_utils.h
+++ b/taichi/runtime/metal/runtime_utils.h
@@ -2,8 +2,7 @@
 
 #include <cstddef>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class MemoryPool;
 
@@ -34,5 +33,4 @@ class BufferMemoryView {
 };
 
 }  // namespace metal
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/dx/dx_program.cpp b/taichi/runtime/program_impls/dx/dx_program.cpp
index 670735a2823f5..7e059f0145cd7 100644
--- a/taichi/runtime/program_impls/dx/dx_program.cpp
+++ b/taichi/runtime/program_impls/dx/dx_program.cpp
@@ -7,8 +7,7 @@
 #include "taichi/runtime/gfx/snode_tree_manager.h"
 #include "taichi/runtime/gfx/aot_module_loader_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 FunctionType compile_to_executable(Kernel *kernel,
@@ -90,7 +89,6 @@ std::unique_ptr<aot::Kernel> Dx11ProgramImpl::make_aot_kernel(Kernel &kernel) {
   return std::make_unique<gfx::KernelImpl>(runtime_.get(), std::move(kparams));
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif
diff --git a/taichi/runtime/program_impls/dx/dx_program.h b/taichi/runtime/program_impls/dx/dx_program.h
index 87f39fa7675ce..372fcc1e8a8d3 100644
--- a/taichi/runtime/program_impls/dx/dx_program.h
+++ b/taichi/runtime/program_impls/dx/dx_program.h
@@ -6,8 +6,7 @@
 #include "taichi/runtime/gfx/snode_tree_manager.h"
 #include "taichi/program/program_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Dx11ProgramImpl : public ProgramImpl {
  public:
@@ -71,7 +70,6 @@ class Dx11ProgramImpl : public ProgramImpl {
   std::vector<spirv::CompiledSNodeStructs> aot_compiled_snode_structs_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif
diff --git a/taichi/runtime/program_impls/llvm/llvm_program.cpp b/taichi/runtime/program_impls/llvm/llvm_program.cpp
index 9aea9a0801ea2..27bc757908fb3 100644
--- a/taichi/runtime/program_impls/llvm/llvm_program.cpp
+++ b/taichi/runtime/program_impls/llvm/llvm_program.cpp
@@ -20,8 +20,7 @@
 #include "taichi/codegen/dx12/codegen_dx12.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 LlvmProgramImpl::LlvmProgramImpl(CompileConfig &config_,
                                  KernelProfilerBase *profiler)
@@ -193,5 +192,4 @@ LlvmProgramImpl *get_llvm_program(Program *prog) {
   return llvm_prog;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/llvm/llvm_program.h b/taichi/runtime/program_impls/llvm/llvm_program.h
index 2c5ab68e07faf..dad6f995ad81f 100644
--- a/taichi/runtime/program_impls/llvm/llvm_program.h
+++ b/taichi/runtime/program_impls/llvm/llvm_program.h
@@ -17,8 +17,7 @@ namespace llvm {
 class Module;
 }  // namespace llvm
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class StructCompiler;
 class Program;
@@ -299,5 +298,4 @@ class LlvmProgramImpl : public ProgramImpl {
 
 LlvmProgramImpl *get_llvm_program(Program *prog);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/metal/metal_program.cpp b/taichi/runtime/program_impls/metal/metal_program.cpp
index 8f1a6919c8f5a..482acde54832c 100644
--- a/taichi/runtime/program_impls/metal/metal_program.cpp
+++ b/taichi/runtime/program_impls/metal/metal_program.cpp
@@ -4,8 +4,7 @@
 #include "taichi/codegen/metal/codegen_metal.h"
 #include "taichi/codegen/metal/struct_metal.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 std::unordered_set<const SNode *> find_all_dense_snodes(
@@ -123,5 +122,4 @@ DeviceAllocation MetalProgramImpl::allocate_memory_ndarray(
   return metal_kernel_mgr_->allocate_memory(params);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/metal/metal_program.h b/taichi/runtime/program_impls/metal/metal_program.h
index 55ba519f26756..81fd03c65bcfd 100644
--- a/taichi/runtime/program_impls/metal/metal_program.h
+++ b/taichi/runtime/program_impls/metal/metal_program.h
@@ -13,8 +13,7 @@
 #include "taichi/codegen/metal/struct_metal.h"
 #include "taichi/program/program_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class MetalProgramImpl : public ProgramImpl {
  public:
@@ -56,5 +55,4 @@ class MetalProgramImpl : public ProgramImpl {
   std::unique_ptr<metal::KernelManager> metal_kernel_mgr_{nullptr};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/opengl/opengl_program.cpp b/taichi/runtime/program_impls/opengl/opengl_program.cpp
index 4df1cad1db3ad..bf219a24acb3a 100644
--- a/taichi/runtime/program_impls/opengl/opengl_program.cpp
+++ b/taichi/runtime/program_impls/opengl/opengl_program.cpp
@@ -5,8 +5,7 @@
 #include "taichi/runtime/gfx/aot_module_builder_impl.h"
 #include "taichi/runtime/gfx/aot_module_loader_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 
@@ -120,5 +119,4 @@ const std::unique_ptr<gfx::CacheManager>
   return cache_manager_;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/opengl/opengl_program.h b/taichi/runtime/program_impls/opengl/opengl_program.h
index 7965c9221b22a..9c901d02ad17f 100644
--- a/taichi/runtime/program_impls/opengl/opengl_program.h
+++ b/taichi/runtime/program_impls/opengl/opengl_program.h
@@ -5,8 +5,7 @@
 #include "taichi/runtime/gfx/snode_tree_manager.h"
 #include "taichi/program/program_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class OpenglProgramImpl : public ProgramImpl {
  public:
@@ -76,5 +75,4 @@ class OpenglProgramImpl : public ProgramImpl {
   std::unique_ptr<gfx::CacheManager> cache_manager_{nullptr};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/vulkan/vulkan_program.cpp b/taichi/runtime/program_impls/vulkan/vulkan_program.cpp
index 9d1ac33268ce7..3e5990aa15935 100644
--- a/taichi/runtime/program_impls/vulkan/vulkan_program.cpp
+++ b/taichi/runtime/program_impls/vulkan/vulkan_program.cpp
@@ -13,8 +13,7 @@
 
 using namespace taichi::lang::vulkan;
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 std::vector<std::string> get_required_instance_extensions() {
@@ -255,5 +254,4 @@ VulkanProgramImpl::~VulkanProgramImpl() {
   embedded_device_.reset();
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/program_impls/vulkan/vulkan_program.h b/taichi/runtime/program_impls/vulkan/vulkan_program.h
index 9a8edd8b2232a..23ec65be117aa 100644
--- a/taichi/runtime/program_impls/vulkan/vulkan_program.h
+++ b/taichi/runtime/program_impls/vulkan/vulkan_program.h
@@ -22,8 +22,7 @@
 
 #include <optional>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace vulkan {
 class VulkanDeviceCreator;
@@ -110,5 +109,4 @@ class VulkanProgramImpl : public ProgramImpl {
   std::vector<spirv::CompiledSNodeStructs> aot_compiled_snode_structs_;
   std::unique_ptr<gfx::CacheManager> cache_manager_{nullptr};
 };
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/runtime.cpp b/taichi/runtime/runtime.cpp
index 51b055279d065..3e472bb69e43e 100644
--- a/taichi/runtime/runtime.cpp
+++ b/taichi/runtime/runtime.cpp
@@ -1,6 +1,6 @@
 #include "taichi/runtime/runtime.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 std::unique_ptr<Runtime> Runtime::create(Arch arch) {
   auto &factories = get_factories();
@@ -11,4 +11,4 @@ std::unique_ptr<Runtime> Runtime::create(Arch arch) {
   }
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/runtime.h b/taichi/runtime/runtime.h
index 726fe1114ee92..a91230905334c 100644
--- a/taichi/runtime/runtime.h
+++ b/taichi/runtime/runtime.h
@@ -8,7 +8,7 @@
 #include <memory>
 #include <functional>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class Runtime {
  protected:
@@ -52,4 +52,4 @@ void Runtime::register_impl(Arch arch) {
   factories[arch] = [] { return std::make_unique<RuntimeT>(); };
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/runtime/wasm/aot_module_builder_impl.cpp b/taichi/runtime/wasm/aot_module_builder_impl.cpp
index 5fb07369ee5fc..d50e881c63d19 100644
--- a/taichi/runtime/wasm/aot_module_builder_impl.cpp
+++ b/taichi/runtime/wasm/aot_module_builder_impl.cpp
@@ -6,8 +6,7 @@
 #include "taichi/util/file_sequence_writer.h"
 #include "llvm/Linker/Linker.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace wasm {
 
 AotModuleBuilderImpl::AotModuleBuilderImpl() : module_(nullptr) {
@@ -61,5 +60,4 @@ void AotModuleBuilderImpl::add_per_backend_tmpl(const std::string &identifier,
 }
 
 }  // namespace wasm
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/runtime/wasm/aot_module_builder_impl.h b/taichi/runtime/wasm/aot_module_builder_impl.h
index d9d243e9f8b04..8be7db8774834 100644
--- a/taichi/runtime/wasm/aot_module_builder_impl.h
+++ b/taichi/runtime/wasm/aot_module_builder_impl.h
@@ -9,8 +9,7 @@
 
 #include "taichi/codegen/wasm/codegen_wasm.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace wasm {
 
 class AotModuleBuilderImpl : public AotModuleBuilder {
@@ -40,5 +39,4 @@ class AotModuleBuilderImpl : public AotModuleBuilder {
 };
 
 }  // namespace wasm
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/struct/snode_tree.cpp b/taichi/struct/snode_tree.cpp
index 0f1ec96beae63..c484b827c8ea5 100644
--- a/taichi/struct/snode_tree.cpp
+++ b/taichi/struct/snode_tree.cpp
@@ -1,7 +1,6 @@
 #include "taichi/struct/snode_tree.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 void get_snodes_to_root_id_impl(const SNode &node,
@@ -39,5 +38,4 @@ std::unordered_map<int, int> get_snodes_to_root_id(const SNode &root) {
   return res;
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/struct/snode_tree.h b/taichi/struct/snode_tree.h
index a22b7691392f1..f6c84b1b2afdf 100644
--- a/taichi/struct/snode_tree.h
+++ b/taichi/struct/snode_tree.h
@@ -5,8 +5,7 @@
 
 #include "taichi/ir/snode.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 /**
  * Represents a tree of SNodes.
@@ -52,5 +51,4 @@ class SNodeTree {
  */
 std::unordered_map<int, int> get_snodes_to_root_id(const SNode &root);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/struct/struct.cpp b/taichi/struct/struct.cpp
index 165609f48e92b..4cd4a26c6869d 100644
--- a/taichi/struct/struct.cpp
+++ b/taichi/struct/struct.cpp
@@ -2,8 +2,7 @@
 
 #include "struct.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 void StructCompiler::collect_snodes(SNode &snode) {
   snodes.push_back(&snode);
@@ -13,5 +12,4 @@ void StructCompiler::collect_snodes(SNode &snode) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/struct/struct.h b/taichi/struct/struct.h
index a2b7282834aa3..52061acf9f048 100644
--- a/taichi/struct/struct.h
+++ b/taichi/struct/struct.h
@@ -3,8 +3,7 @@
 
 #include "taichi/ir/snode.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class StructCompiler {
  public:
@@ -24,5 +23,4 @@ class StructCompiler {
   virtual void run(SNode &node) = 0;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/system/benchmark.h b/taichi/system/benchmark.h
index fd1ca6d24f8bb..058df3657f182 100644
--- a/taichi/system/benchmark.h
+++ b/taichi/system/benchmark.h
@@ -8,7 +8,7 @@
 #include "taichi/common/interface.h"
 #include "taichi/system/timer.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class Benchmark : public Unit {
  protected:
@@ -61,4 +61,4 @@ class Benchmark : public Unit {
 
 TI_INTERFACE(Benchmark)
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/demangling.cpp b/taichi/system/demangling.cpp
index 5059905885fb8..23938c11d6721 100644
--- a/taichi/system/demangling.cpp
+++ b/taichi/system/demangling.cpp
@@ -9,7 +9,7 @@
 #include <cxxabi.h>
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 // From https://en.wikipedia.org/wiki/Name_mangling
 
@@ -45,4 +45,4 @@ class Demangling : public Task {
 
 TI_IMPLEMENTATION(Task, Demangling, "demangle")
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/dynamic_loader.cpp b/taichi/system/dynamic_loader.cpp
index e1a866d74d88e..1bef078f664e8 100644
--- a/taichi/system/dynamic_loader.cpp
+++ b/taichi/system/dynamic_loader.cpp
@@ -6,7 +6,7 @@
 #include <dlfcn.h>
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 DynamicLoader::DynamicLoader(const std::string &dll_path) {
   load_dll(dll_path);
@@ -52,4 +52,4 @@ bool DynamicLoader::loaded() const {
   return dll_ != nullptr;
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/dynamic_loader.h b/taichi/system/dynamic_loader.h
index 3812f13555960..8e544c2b592f9 100644
--- a/taichi/system/dynamic_loader.h
+++ b/taichi/system/dynamic_loader.h
@@ -7,7 +7,7 @@
 
 #include "taichi/common/core.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class DynamicLoader {
  private:
@@ -33,4 +33,4 @@ class DynamicLoader {
   void *dll_ = nullptr;
 };
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/memory_pool.cpp b/taichi/system/memory_pool.cpp
index c98a908a90cfd..45f6c2ec111f2 100644
--- a/taichi/system/memory_pool.cpp
+++ b/taichi/system/memory_pool.cpp
@@ -3,8 +3,7 @@
 #include "taichi/rhi/cuda/cuda_driver.h"
 #include "taichi/rhi/cuda/cuda_device.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // In the future we wish to move the MemoryPool inside each Device
 // so that the memory allocated from each Device can be used as-is.
@@ -137,5 +136,4 @@ MemoryPool::~MemoryPool() {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/system/memory_pool.h b/taichi/system/memory_pool.h
index 25da2e840ddf0..06dce540d3ad5 100644
--- a/taichi/system/memory_pool.h
+++ b/taichi/system/memory_pool.h
@@ -10,8 +10,7 @@
 #include <memory>
 #include <thread>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // A memory pool that runs on the host
 
@@ -55,5 +54,4 @@ class TI_DLL_EXPORT MemoryPool {
   Device *device_;
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/system/profiler.cpp b/taichi/system/profiler.cpp
index 7130d137520a2..1ffa86ae3e258 100644
--- a/taichi/system/profiler.cpp
+++ b/taichi/system/profiler.cpp
@@ -1,7 +1,7 @@
 #include "taichi/system/profiler.h"
 #include "spdlog/fmt/bundled/color.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 // A profiler's records form a tree structure
 struct ProfilerRecordNode {
@@ -278,4 +278,4 @@ void Profiling::clear_profile_info() {
   }
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/profiler.h b/taichi/system/profiler.h
index 4a6bcf278348a..c71c39b131ced 100644
--- a/taichi/system/profiler.h
+++ b/taichi/system/profiler.h
@@ -14,7 +14,7 @@
 #include "taichi/common/core.h"
 #include "taichi/system/timer.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class ProfilerRecords;
 
@@ -56,4 +56,4 @@ class Profiling {
 
 #define TI_AUTO_PROF TI_PROFILER(__FUNCTION__)
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/run_tests.cpp b/taichi/system/run_tests.cpp
index 68628afd44f92..03c8eaed6dc29 100644
--- a/taichi/system/run_tests.cpp
+++ b/taichi/system/run_tests.cpp
@@ -7,7 +7,7 @@
 #include "taichi/common/task.h"
 #include "taichi/util/testing.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class RunTests : public Task {
   std::string run(const std::vector<std::string> &parameters) override {
@@ -17,4 +17,4 @@ class RunTests : public Task {
 
 TI_IMPLEMENTATION(Task, RunTests, "test");
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/threading.cpp b/taichi/system/threading.cpp
index 06fcf7955ee63..f85caf9ffd2e3 100644
--- a/taichi/system/threading.cpp
+++ b/taichi/system/threading.cpp
@@ -10,7 +10,7 @@
 #include <thread>
 #include <vector>
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 bool test_threading() {
   auto tp = ThreadPool(20);
@@ -136,4 +136,4 @@ ThreadPool::~ThreadPool() {
     th.join();
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/threading.h b/taichi/system/threading.h
index aca157079013b..002e972b28336 100644
--- a/taichi/system/threading.h
+++ b/taichi/system/threading.h
@@ -12,7 +12,7 @@
 #include <functional>
 #include <thread>
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 using RangeForTaskFunc = void(void *, int thread_id, int i);
 using ParallelFor = void(int n, int num_threads, void *, RangeForTaskFunc func);
@@ -59,4 +59,4 @@ class ThreadPool {
   ~ThreadPool();
 };
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/timeline.cpp b/taichi/system/timeline.cpp
index 3c02cb8b0f3af..a6fd28026eeda 100644
--- a/taichi/system/timeline.cpp
+++ b/taichi/system/timeline.cpp
@@ -1,6 +1,6 @@
 #include "taichi/system/timeline.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 std::string TimelineEvent::to_json() {
   std::string json{"{"};
@@ -122,4 +122,4 @@ void Timelines::set_enabled(bool enabled) {
   enabled_ = enabled;
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/timeline.h b/taichi/system/timeline.h
index cf303c0269d79..3fb289f8d5808 100644
--- a/taichi/system/timeline.h
+++ b/taichi/system/timeline.h
@@ -6,7 +6,7 @@
 #include "taichi/common/core.h"
 #include "taichi/system/timer.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 struct TimelineEvent {
   std::string name;
@@ -88,4 +88,4 @@ class Timelines {
 
 #define TI_AUTO_TIMELINE TI_TIMELINE(__FUNCTION__)
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/timer.cpp b/taichi/system/timer.cpp
index fb0d61472e231..c943e0eeebc43 100644
--- a/taichi/system/timer.cpp
+++ b/taichi/system/timer.cpp
@@ -11,7 +11,7 @@
 
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 using namespace std;
 
@@ -232,4 +232,4 @@ uint64 Time::get_cycles() {
 
 #endif
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/timer.h b/taichi/system/timer.h
index d9ccf2e19ea31..e770ad6147b6a 100644
--- a/taichi/system/timer.h
+++ b/taichi/system/timer.h
@@ -18,7 +18,7 @@
 #pragma warning(pop)
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 #define TIME(x)                                                      \
   {                                                                  \
@@ -105,4 +105,4 @@ class TI_DLL_EXPORT Time {
   };
 };
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/traceback.cpp b/taichi/system/traceback.cpp
index 46e2e660bdeef..ee9054050b2e8 100644
--- a/taichi/system/traceback.cpp
+++ b/taichi/system/traceback.cpp
@@ -195,7 +195,7 @@ inline std::vector<StackFrame> stack_trace() {
 #include <cxxabi.h>
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void print_traceback() {
 #ifdef __APPLE__
@@ -367,4 +367,4 @@ void print_traceback() {
       "https://docs.taichi-lang.org/docs/install\n");
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/system/unified_allocator.cpp b/taichi/system/unified_allocator.cpp
index a7ad7fdcebcee..229587e45af83 100644
--- a/taichi/system/unified_allocator.cpp
+++ b/taichi/system/unified_allocator.cpp
@@ -13,7 +13,7 @@
 #include "taichi/rhi/cpu/cpu_device.h"
 #include <string>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 UnifiedAllocator::UnifiedAllocator(std::size_t size, Arch arch, Device *device)
     : size_(size), arch_(arch), device_(device) {
@@ -59,4 +59,4 @@ void taichi::lang::UnifiedAllocator::memset(unsigned char val) {
   std::memset(data, val, size_);
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/system/unified_allocator.h b/taichi/system/unified_allocator.h
index 47a59c53f4e2f..b781391c9226d 100644
--- a/taichi/system/unified_allocator.h
+++ b/taichi/system/unified_allocator.h
@@ -10,7 +10,7 @@ namespace taichi {
 class VirtualMemoryAllocator;
 }
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // This class can only have one instance
 class UnifiedAllocator {
@@ -60,4 +60,4 @@ class UnifiedAllocator {
   Device *device_{nullptr};
 };
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/system/virtual_memory.h b/taichi/system/virtual_memory.h
index 47ee75ee15a61..b8629f0b71017 100644
--- a/taichi/system/virtual_memory.h
+++ b/taichi/system/virtual_memory.h
@@ -8,7 +8,7 @@
 #include "taichi/platform/windows/windows.h"
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 // Cross-platform virtual memory allocator
 class VirtualMemoryAllocator {
@@ -59,4 +59,4 @@ uint64 get_memory_usage(int pid = -1);
 #define TI_MEMORY_USAGE(name) \
   TI_DEBUG("Memory Usage [{}] = {:.2f} GB", name, get_memory_usage_gb());
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/transforms/alg_simp.cpp b/taichi/transforms/alg_simp.cpp
index 8b84e55ea7ea9..07dc81f8ef738 100644
--- a/taichi/transforms/alg_simp.cpp
+++ b/taichi/transforms/alg_simp.cpp
@@ -6,7 +6,7 @@
 #include "taichi/program/program.h"
 #include "taichi/util/bit.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Algebraic Simplification and Strength Reduction
 class AlgSimp : public BasicStmtVisitor {
@@ -445,4 +445,4 @@ bool alg_simp(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/auto_diff.cpp b/taichi/transforms/auto_diff.cpp
index 3a3dc6e4f4560..9e6cdcf84421c 100644
--- a/taichi/transforms/auto_diff.cpp
+++ b/taichi/transforms/auto_diff.cpp
@@ -8,7 +8,7 @@
 #include <typeinfo>
 #include <algorithm>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 class IndependentBlocksJudger : public BasicStmtVisitor {
  public:
   using BasicStmtVisitor::visit;
@@ -1612,4 +1612,4 @@ void differentiation_validation_check(IRNode *root,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/binary_op_simplify.cpp b/taichi/transforms/binary_op_simplify.cpp
index 129e4f66258c7..7ad2b4ff3e73a 100644
--- a/taichi/transforms/binary_op_simplify.cpp
+++ b/taichi/transforms/binary_op_simplify.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class BinaryOpSimp : public BasicStmtVisitor {
  public:
@@ -192,4 +192,4 @@ bool binary_op_simplify(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/bit_loop_vectorize.cpp b/taichi/transforms/bit_loop_vectorize.cpp
index a269b05144b35..298521da03558 100644
--- a/taichi/transforms/bit_loop_vectorize.cpp
+++ b/taichi/transforms/bit_loop_vectorize.cpp
@@ -8,7 +8,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/ir/analysis.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class BitLoopVectorize : public IRVisitor {
  public:
@@ -335,4 +335,4 @@ void bit_loop_vectorize(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/cfg_optimization.cpp b/taichi/transforms/cfg_optimization.cpp
index 9366300f06ec1..24a5dd96bd17a 100644
--- a/taichi/transforms/cfg_optimization.cpp
+++ b/taichi/transforms/cfg_optimization.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass {
 bool cfg_optimization(
@@ -35,4 +35,4 @@ bool cfg_optimization(
 }
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/check_out_of_bound.cpp b/taichi/transforms/check_out_of_bound.cpp
index ca025ffbad3b3..d09b2f12bc8c2 100644
--- a/taichi/transforms/check_out_of_bound.cpp
+++ b/taichi/transforms/check_out_of_bound.cpp
@@ -6,7 +6,7 @@
 #include "taichi/transforms/utils.h"
 #include <set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // TODO: also check RangeAssumptionStmt
 
@@ -160,4 +160,4 @@ bool check_out_of_bound(IRNode *root,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/check_out_of_bound.h b/taichi/transforms/check_out_of_bound.h
index a1d09831c9a0e..c9a54c2d2e2c6 100644
--- a/taichi/transforms/check_out_of_bound.h
+++ b/taichi/transforms/check_out_of_bound.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class CheckOutOfBoundPass : public Pass {
  public:
@@ -14,5 +13,4 @@ class CheckOutOfBoundPass : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/compile_to_offloads.cpp b/taichi/transforms/compile_to_offloads.cpp
index 58d00e0c2332f..f321f99cb423f 100644
--- a/taichi/transforms/compile_to_offloads.cpp
+++ b/taichi/transforms/compile_to_offloads.cpp
@@ -8,7 +8,7 @@
 #include "taichi/program/function.h"
 #include "taichi/program/kernel.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass {
 namespace {
@@ -359,4 +359,4 @@ void compile_function(IRNode *ir,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/constant_fold.cpp b/taichi/transforms/constant_fold.cpp
index 0596256ad664f..3d87a9f6fe0c4 100644
--- a/taichi/transforms/constant_fold.cpp
+++ b/taichi/transforms/constant_fold.cpp
@@ -11,7 +11,7 @@
 #include "taichi/transforms/constant_fold.h"
 #include "taichi/program/program.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class ConstantFold : public BasicStmtVisitor {
  public:
@@ -266,4 +266,4 @@ bool constant_fold(IRNode *root,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/constant_fold.h b/taichi/transforms/constant_fold.h
index c7ffbbcfde9a6..69581c7489715 100644
--- a/taichi/transforms/constant_fold.h
+++ b/taichi/transforms/constant_fold.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class ConstantFoldPass : public Pass {
  public:
@@ -14,5 +13,4 @@ class ConstantFoldPass : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/demote_atomics.cpp b/taichi/transforms/demote_atomics.cpp
index 1db0483589703..e2de05d4958ae 100644
--- a/taichi/transforms/demote_atomics.cpp
+++ b/taichi/transforms/demote_atomics.cpp
@@ -8,7 +8,7 @@
 #include <deque>
 #include <set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class DemoteAtomics : public BasicStmtVisitor {
  private:
@@ -195,4 +195,4 @@ bool demote_atomics(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/demote_dense_struct_fors.cpp b/taichi/transforms/demote_dense_struct_fors.cpp
index c7ef6d25293a2..55ba8c780c7f7 100644
--- a/taichi/transforms/demote_dense_struct_fors.cpp
+++ b/taichi/transforms/demote_dense_struct_fors.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/transforms/utils.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -193,4 +193,4 @@ void demote_dense_struct_fors(IRNode *root, bool packed) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/demote_mesh_statements.cpp b/taichi/transforms/demote_mesh_statements.cpp
index d7572f1efa826..87dfaae65a15e 100644
--- a/taichi/transforms/demote_mesh_statements.cpp
+++ b/taichi/transforms/demote_mesh_statements.cpp
@@ -5,8 +5,7 @@
 #include "taichi/transforms/demote_mesh_statements.h"
 #include "taichi/ir/visitors.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 const PassID DemoteMeshStatements::id = "DemoteMeshStatements";
 
@@ -153,5 +152,4 @@ void demote_mesh_statements(IRNode *root,
 }
 
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/demote_mesh_statements.h b/taichi/transforms/demote_mesh_statements.h
index dad295315d7fb..4652a4f0367fe 100644
--- a/taichi/transforms/demote_mesh_statements.h
+++ b/taichi/transforms/demote_mesh_statements.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class DemoteMeshStatements : public Pass {
  public:
@@ -14,5 +13,4 @@ class DemoteMeshStatements : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/demote_no_access_mesh_fors.cpp b/taichi/transforms/demote_no_access_mesh_fors.cpp
index 0f2fc28c4efdd..3688f6c923239 100644
--- a/taichi/transforms/demote_no_access_mesh_fors.cpp
+++ b/taichi/transforms/demote_no_access_mesh_fors.cpp
@@ -5,7 +5,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/transforms/utils.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -69,4 +69,4 @@ void demote_no_access_mesh_fors(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/demote_operations.cpp b/taichi/transforms/demote_operations.cpp
index cc3a65ab2e345..56b191d8b0f3d 100644
--- a/taichi/transforms/demote_operations.cpp
+++ b/taichi/transforms/demote_operations.cpp
@@ -5,7 +5,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/program/program.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Demote Operations into pieces for backends to deal easier
 class DemoteOperations : public BasicStmtVisitor {
@@ -229,4 +229,4 @@ bool demote_operations(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/detect_read_only.cpp b/taichi/transforms/detect_read_only.cpp
index c0e2825d4b36a..e3f5a72077c54 100644
--- a/taichi/transforms/detect_read_only.cpp
+++ b/taichi/transforms/detect_read_only.cpp
@@ -6,7 +6,7 @@
 
 #include <algorithm>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass {
 
@@ -92,4 +92,4 @@ std::unordered_map<int, ExternalPtrAccess> detect_external_ptr_access_in_task(
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/determine_ad_stack_size.cpp b/taichi/transforms/determine_ad_stack_size.cpp
index 8083303e0be8b..090e755c38a71 100644
--- a/taichi/transforms/determine_ad_stack_size.cpp
+++ b/taichi/transforms/determine_ad_stack_size.cpp
@@ -7,8 +7,7 @@
 #include <queue>
 #include <unordered_map>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace irpass {
 
@@ -29,5 +28,4 @@ bool determine_ad_stack_size(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/die.cpp b/taichi/transforms/die.cpp
index f6d696c4da498..7a83e8faf3fe3 100644
--- a/taichi/transforms/die.cpp
+++ b/taichi/transforms/die.cpp
@@ -8,7 +8,7 @@
 
 #include <unordered_set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Dead Instruction Elimination
 class DIE : public IRVisitor {
@@ -127,4 +127,4 @@ bool die(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/extract_constant.cpp b/taichi/transforms/extract_constant.cpp
index d7db7c76e01ea..a67bf86f38592 100644
--- a/taichi/transforms/extract_constant.cpp
+++ b/taichi/transforms/extract_constant.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/program/compile_config.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class ExtractConstant : public BasicStmtVisitor {
  private:
@@ -61,4 +61,4 @@ bool extract_constant(IRNode *root, const CompileConfig &config) {
 }
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/flag_access.cpp b/taichi/transforms/flag_access.cpp
index bf754b518dc1e..2005aa464aea4 100644
--- a/taichi/transforms/flag_access.cpp
+++ b/taichi/transforms/flag_access.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Flag accesses to be either weak (non-activating) or strong (activating)
 class FlagAccess : public IRVisitor {
@@ -176,4 +176,4 @@ void flag_access(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/frontend_type_check.cpp b/taichi/transforms/frontend_type_check.cpp
index 49bcbdb194e1d..01b97c9d5a47d 100644
--- a/taichi/transforms/frontend_type_check.cpp
+++ b/taichi/transforms/frontend_type_check.cpp
@@ -2,8 +2,7 @@
 #include "taichi/ir/frontend_ir.h"
 #include "taichi/ir/statements.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class FrontendTypeCheck : public IRVisitor {
   void check_cond_type(const Expr &cond, std::string stmt_name) {
@@ -102,6 +101,4 @@ void frontend_type_check(IRNode *root) {
 
 }  // namespace irpass
 
-}  // namespace lang
-
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/inlining.cpp b/taichi/transforms/inlining.cpp
index 60a317ca1ab87..6c2ff42597e87 100644
--- a/taichi/transforms/inlining.cpp
+++ b/taichi/transforms/inlining.cpp
@@ -6,8 +6,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // Inline all functions.
 class Inliner : public BasicStmtVisitor {
@@ -92,5 +91,4 @@ bool inlining(IRNode *root,
 
 }  // namespace irpass
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/inlining.h b/taichi/transforms/inlining.h
index 71191b42d0058..ee771101f2d66 100644
--- a/taichi/transforms/inlining.h
+++ b/taichi/transforms/inlining.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class InliningPass : public Pass {
  public:
@@ -12,5 +11,4 @@ class InliningPass : public Pass {
   struct Args {};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/insert_scratch_pad.cpp b/taichi/transforms/insert_scratch_pad.cpp
index 38f6e59c4cce0..4624506ee2912 100644
--- a/taichi/transforms/insert_scratch_pad.cpp
+++ b/taichi/transforms/insert_scratch_pad.cpp
@@ -6,7 +6,7 @@
 #include "taichi/ir/scratch_pad.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // TODO: rename scratch_pad to block_local_cache? Need to get rid of the
 // scratch_pad term
@@ -33,4 +33,4 @@ std::unique_ptr<ScratchPads> initialize_scratch_pad(OffloadedStmt *offload) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/ir_printer.cpp b/taichi/transforms/ir_printer.cpp
index 599c0e1661357..0bf6a641814cf 100644
--- a/taichi/transforms/ir_printer.cpp
+++ b/taichi/transforms/ir_printer.cpp
@@ -8,7 +8,7 @@
 #include "taichi/ir/frontend_ir.h"
 #include "taichi/util/str.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -836,4 +836,4 @@ void print(IRNode *root, std::string *output) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/loop_invariant_code_motion.cpp b/taichi/transforms/loop_invariant_code_motion.cpp
index 8e9fc4c4f9a11..6ab20e0fc43b7 100644
--- a/taichi/transforms/loop_invariant_code_motion.cpp
+++ b/taichi/transforms/loop_invariant_code_motion.cpp
@@ -1,6 +1,6 @@
 #include "taichi/transforms/loop_invariant_detector.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class LoopInvariantCodeMotion : public LoopInvariantDetector {
  public:
@@ -88,4 +88,4 @@ bool loop_invariant_code_motion(IRNode *root, const CompileConfig &config) {
 }
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/lower_access.cpp b/taichi/transforms/lower_access.cpp
index 1597fb68157b5..9cbd90c226d6a 100644
--- a/taichi/transforms/lower_access.cpp
+++ b/taichi/transforms/lower_access.cpp
@@ -11,8 +11,7 @@
 #include <deque>
 #include <set>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 class LowerAccess;
@@ -297,5 +296,4 @@ bool lower_access(IRNode *root,
 }
 
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/lower_access.h b/taichi/transforms/lower_access.h
index 858af5a215414..68f764fbddd1c 100644
--- a/taichi/transforms/lower_access.h
+++ b/taichi/transforms/lower_access.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class LowerAccessPass : public Pass {
  public:
@@ -15,5 +14,4 @@ class LowerAccessPass : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/lower_ast.cpp b/taichi/transforms/lower_ast.cpp
index 462c3ddc1862f..d3703e102dfee 100644
--- a/taichi/transforms/lower_ast.cpp
+++ b/taichi/transforms/lower_ast.cpp
@@ -8,7 +8,7 @@
 
 #include <unordered_set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -522,4 +522,4 @@ void lower_ast(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/lower_matrix_ptr.cpp b/taichi/transforms/lower_matrix_ptr.cpp
index 3626337f37679..658e0a976378c 100644
--- a/taichi/transforms/lower_matrix_ptr.cpp
+++ b/taichi/transforms/lower_matrix_ptr.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class LowerMatrixPtr : public BasicStmtVisitor {
  public:
@@ -57,4 +57,4 @@ void lower_matrix_ptr(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/make_block_local.cpp b/taichi/transforms/make_block_local.cpp
index e8af196a3f989..749a62bd5a863 100644
--- a/taichi/transforms/make_block_local.cpp
+++ b/taichi/transforms/make_block_local.cpp
@@ -5,7 +5,7 @@
 #include "taichi/ir/scratch_pad.h"
 #include "taichi/transforms/make_block_local.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -358,4 +358,4 @@ void make_block_local(IRNode *root,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/make_block_local.h b/taichi/transforms/make_block_local.h
index fc0ed3f7a1ca1..1fa35741aba64 100644
--- a/taichi/transforms/make_block_local.h
+++ b/taichi/transforms/make_block_local.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class MakeBlockLocalPass : public Pass {
  public:
@@ -14,5 +13,4 @@ class MakeBlockLocalPass : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/make_mesh_block_local.cpp b/taichi/transforms/make_mesh_block_local.cpp
index c098e9db63398..a9c85766aabff 100644
--- a/taichi/transforms/make_mesh_block_local.cpp
+++ b/taichi/transforms/make_mesh_block_local.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/transforms/make_mesh_block_local.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 const PassID MakeMeshBlockLocal::id = "MakeMeshBlockLocal";
 
@@ -673,5 +672,4 @@ void make_mesh_block_local(IRNode *root,
 }
 
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/make_mesh_block_local.h b/taichi/transforms/make_mesh_block_local.h
index 04d8ce04479b0..9b8b6f354544f 100644
--- a/taichi/transforms/make_mesh_block_local.h
+++ b/taichi/transforms/make_mesh_block_local.h
@@ -6,8 +6,7 @@
 
 #include <set>
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class MakeMeshBlockLocal : public Pass {
  public:
@@ -70,5 +69,4 @@ class MakeMeshBlockLocal : public Pass {
   int mapping_dtype_size_{0};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/make_mesh_thread_local.cpp b/taichi/transforms/make_mesh_thread_local.cpp
index ee85ce5dd2ae7..f7209fef73510 100644
--- a/taichi/transforms/make_mesh_thread_local.cpp
+++ b/taichi/transforms/make_mesh_thread_local.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/transforms/make_mesh_thread_local.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 const PassID MakeMeshThreadLocal::id = "MakeMeshThreadLocal";
 
@@ -161,5 +160,4 @@ void make_mesh_thread_local(IRNode *root,
 }
 
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/make_mesh_thread_local.h b/taichi/transforms/make_mesh_thread_local.h
index aa054a1548456..e383895b645df 100644
--- a/taichi/transforms/make_mesh_thread_local.h
+++ b/taichi/transforms/make_mesh_thread_local.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class MakeMeshThreadLocal : public Pass {
  public:
@@ -14,5 +13,4 @@ class MakeMeshThreadLocal : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/make_thread_local.cpp b/taichi/transforms/make_thread_local.cpp
index dc58270f13d27..d88e8fcd946af 100644
--- a/taichi/transforms/make_thread_local.cpp
+++ b/taichi/transforms/make_thread_local.cpp
@@ -10,7 +10,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -207,4 +207,4 @@ void make_thread_local(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/offload.cpp b/taichi/transforms/offload.cpp
index 822e7a09b3283..4862c35b6ec6f 100644
--- a/taichi/transforms/offload.cpp
+++ b/taichi/transforms/offload.cpp
@@ -9,7 +9,7 @@
 #include <unordered_map>
 #include <utility>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass {
 namespace {
@@ -789,4 +789,4 @@ void offload(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/optimize_bit_struct_stores.cpp b/taichi/transforms/optimize_bit_struct_stores.cpp
index e6302e05ae5f6..187f644846d7e 100644
--- a/taichi/transforms/optimize_bit_struct_stores.cpp
+++ b/taichi/transforms/optimize_bit_struct_stores.cpp
@@ -192,7 +192,7 @@ class DemoteAtomicBitStructStores : public BasicStmtVisitor {
 
 }  // namespace
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass {
 void optimize_bit_struct_stores(IRNode *root,
@@ -216,4 +216,4 @@ void optimize_bit_struct_stores(IRNode *root,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/re_id.cpp b/taichi/transforms/re_id.cpp
index b0e34abe873e7..61831cce9e29b 100644
--- a/taichi/transforms/re_id.cpp
+++ b/taichi/transforms/re_id.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // This pass manipulates the id of statements so that they are successive values
 // starting from 0
@@ -41,4 +41,4 @@ void re_id(IRNode *root) {
 }
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/remove_assume_in_range.cpp b/taichi/transforms/remove_assume_in_range.cpp
index 79e3ffe9d5409..8011e2a4b240b 100644
--- a/taichi/transforms/remove_assume_in_range.cpp
+++ b/taichi/transforms/remove_assume_in_range.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -40,4 +40,4 @@ bool remove_range_assumption(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/remove_loop_unique.cpp b/taichi/transforms/remove_loop_unique.cpp
index d6ae1ceb71898..51d9ea9d33697 100644
--- a/taichi/transforms/remove_loop_unique.cpp
+++ b/taichi/transforms/remove_loop_unique.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace {
 
@@ -38,4 +38,4 @@ bool remove_loop_unique(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/replace_statements.cpp b/taichi/transforms/replace_statements.cpp
index 08923dd5628b9..39ed4bceca81e 100644
--- a/taichi/transforms/replace_statements.cpp
+++ b/taichi/transforms/replace_statements.cpp
@@ -1,6 +1,6 @@
 #include "taichi/ir/transforms.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass {
 
@@ -27,4 +27,4 @@ bool replace_statements(IRNode *root,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/reverse_segments.cpp b/taichi/transforms/reverse_segments.cpp
index 4065b0278af96..206e9a9ad3e77 100644
--- a/taichi/transforms/reverse_segments.cpp
+++ b/taichi/transforms/reverse_segments.cpp
@@ -6,7 +6,7 @@
 
 #include <set>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 namespace irpass {
 
@@ -82,4 +82,4 @@ void reverse_segments(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/scalar_pointer_lowerer.cpp b/taichi/transforms/scalar_pointer_lowerer.cpp
index 495506cb39cd6..f4e41bd787df6 100644
--- a/taichi/transforms/scalar_pointer_lowerer.cpp
+++ b/taichi/transforms/scalar_pointer_lowerer.cpp
@@ -8,8 +8,7 @@
 #include "taichi/transforms/scalar_pointer_lowerer.h"
 #include "taichi/transforms/utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 ScalarPointerLowerer::ScalarPointerLowerer(SNode *leaf_snode,
                                            const std::vector<Stmt *> &indices,
@@ -100,5 +99,4 @@ void ScalarPointerLowerer::run() {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/scalar_pointer_lowerer.h b/taichi/transforms/scalar_pointer_lowerer.h
index a763ad3a6b2c6..16aa4e1bd1c82 100644
--- a/taichi/transforms/scalar_pointer_lowerer.h
+++ b/taichi/transforms/scalar_pointer_lowerer.h
@@ -4,8 +4,7 @@
 
 #include "taichi/ir/stmt_op_types.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class LinearizeStmt;
 class SNode;
@@ -75,5 +74,4 @@ class ScalarPointerLowerer {
   int path_length_{0};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/scalarize.cpp b/taichi/transforms/scalarize.cpp
index 8f6afbac0d630..a8e452a005398 100644
--- a/taichi/transforms/scalarize.cpp
+++ b/taichi/transforms/scalarize.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 class Scalarize : public IRVisitor {
  public:
@@ -243,4 +243,4 @@ void scalarize(IRNode *root) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/simplify.cpp b/taichi/transforms/simplify.cpp
index 6c18c88a9194d..d1cf6821e3584 100644
--- a/taichi/transforms/simplify.cpp
+++ b/taichi/transforms/simplify.cpp
@@ -11,7 +11,7 @@
 #include <unordered_set>
 #include <utility>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Common subexpression elimination, store forwarding, useless local store
 // elimination; Simplify if statements into conditional stores.
@@ -655,4 +655,4 @@ void full_simplify(IRNode *root,
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/simplify.h b/taichi/transforms/simplify.h
index ada1cec40bd46..9a4c66e45e2ef 100644
--- a/taichi/transforms/simplify.h
+++ b/taichi/transforms/simplify.h
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/pass.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class FullSimplifyPass : public Pass {
  public:
@@ -18,5 +17,4 @@ class FullSimplifyPass : public Pass {
   };
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/statement_usage_replace.cpp b/taichi/transforms/statement_usage_replace.cpp
index a46d104c01aa6..04da24f46e648 100644
--- a/taichi/transforms/statement_usage_replace.cpp
+++ b/taichi/transforms/statement_usage_replace.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Replace all usages statement A with a new statement B.
 // Note that the original statement A is NOT replaced.
@@ -93,4 +93,4 @@ void replace_all_usages_with(IRNode *root, Stmt *old_stmt, Stmt *new_stmt) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/transform_statements.cpp b/taichi/transforms/transform_statements.cpp
index eaae474fafdd9..a6d0d136c6ef2 100644
--- a/taichi/transforms/transform_statements.cpp
+++ b/taichi/transforms/transform_statements.cpp
@@ -3,7 +3,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/ir/visitors.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Transform each filtered statement
 class StatementsTransformer : public BasicStmtVisitor {
@@ -58,4 +58,4 @@ bool transform_statements(
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/type_check.cpp b/taichi/transforms/type_check.cpp
index 080ac7d78a89b..709d11af5141f 100644
--- a/taichi/transforms/type_check.cpp
+++ b/taichi/transforms/type_check.cpp
@@ -7,7 +7,7 @@
 #include "taichi/ir/frontend_ir.h"
 #include "taichi/transforms/utils.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 static_assert(
     sizeof(real) == sizeof(float32),
@@ -568,4 +568,4 @@ void type_check(IRNode *root, const CompileConfig &config) {
 
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/unreachable_code_elimination.cpp b/taichi/transforms/unreachable_code_elimination.cpp
index d22bcdd8e5dbd..ea90f015c5506 100644
--- a/taichi/transforms/unreachable_code_elimination.cpp
+++ b/taichi/transforms/unreachable_code_elimination.cpp
@@ -4,7 +4,7 @@
 #include "taichi/ir/visitors.h"
 #include "taichi/system/profiler.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Unconditionally eliminate ContinueStmt's at **ends** of loops
 class UselessContinueEliminator : public IRVisitor {
@@ -156,4 +156,4 @@ bool unreachable_code_elimination(IRNode *root) {
 }
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/transforms/utils.cpp b/taichi/transforms/utils.cpp
index d3dd28bccf3c2..85cc9ba9142ee 100644
--- a/taichi/transforms/utils.cpp
+++ b/taichi/transforms/utils.cpp
@@ -1,7 +1,6 @@
 #include "taichi/ir/statements.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 Stmt *generate_mod_x_div_y(VecStatement *stmts, Stmt *num, int x, int y) {
   auto const_x = stmts->push_back<ConstStmt>(TypedConstant(x));
@@ -10,5 +9,4 @@ Stmt *generate_mod_x_div_y(VecStatement *stmts, Stmt *num, int x, int y) {
   return stmts->push_back<BinaryOpStmt>(BinaryOpType::div, mod_x, const_y);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/utils.h b/taichi/transforms/utils.h
index 3440be0314b99..7ae4535b58c2e 100644
--- a/taichi/transforms/utils.h
+++ b/taichi/transforms/utils.h
@@ -1,9 +1,7 @@
 #pragma once
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 Stmt *generate_mod_x_div_y(VecStatement *stmts, Stmt *num, int x, int y);
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/transforms/whole_kernel_cse.cpp b/taichi/transforms/whole_kernel_cse.cpp
index 1ecb6c1954032..4391fdd4d4d86 100644
--- a/taichi/transforms/whole_kernel_cse.cpp
+++ b/taichi/transforms/whole_kernel_cse.cpp
@@ -7,7 +7,7 @@
 
 #include <typeindex>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // A helper class to maintain WholeKernelCSE::visited
 class MarkUndone : public BasicStmtVisitor {
@@ -219,4 +219,4 @@ bool whole_kernel_cse(IRNode *root) {
 }
 }  // namespace irpass
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/ui/backends/vulkan/app_context.h b/taichi/ui/backends/vulkan/app_context.h
index 7afebbff987cd..a6dd0b1576b21 100644
--- a/taichi/ui/backends/vulkan/app_context.h
+++ b/taichi/ui/backends/vulkan/app_context.h
@@ -9,11 +9,9 @@
 #include <android/native_window.h>
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class Program;
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 TI_UI_NAMESPACE_BEGIN
 
diff --git a/taichi/ui/backends/vulkan/renderer.h b/taichi/ui/backends/vulkan/renderer.h
index dd9bdc664a83b..0badfe2348b13 100644
--- a/taichi/ui/backends/vulkan/renderer.h
+++ b/taichi/ui/backends/vulkan/renderer.h
@@ -32,11 +32,9 @@
 #include "renderables/lines.h"
 #include "renderables/scene_lines.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class Program;
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 TI_UI_NAMESPACE_BEGIN
 
diff --git a/taichi/ui/backends/vulkan/window.h b/taichi/ui/backends/vulkan/window.h
index d0ebe3a371a1b..e99fa25df8471 100644
--- a/taichi/ui/backends/vulkan/window.h
+++ b/taichi/ui/backends/vulkan/window.h
@@ -23,11 +23,9 @@
 #include "taichi/ui/backends/vulkan/gui.h"
 #include "taichi/program/ndarray.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class Program;
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 TI_UI_NAMESPACE_BEGIN
 
diff --git a/taichi/ui/common/canvas_base.h b/taichi/ui/common/canvas_base.h
index 98af1523b177c..ecfc564dcfee4 100644
--- a/taichi/ui/common/canvas_base.h
+++ b/taichi/ui/common/canvas_base.h
@@ -5,13 +5,11 @@
 #include "taichi/ui/common/renderable_info.h"
 #include "taichi/ui/utils/utils.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class Texture;
 
-}
-}  // namespace taichi
+}  // namespace taichi::lang
 
 TI_UI_NAMESPACE_BEGIN
 
diff --git a/taichi/ui/gui/android.cpp b/taichi/ui/gui/android.cpp
index 2f1e144d44263..ef3f2d95dc534 100644
--- a/taichi/ui/gui/android.cpp
+++ b/taichi/ui/gui/android.cpp
@@ -6,7 +6,7 @@
 #if defined(TI_GUI_ANDROID)
 #include <cstdlib>
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void GUI::process_event() {
   TI_ERROR("GGUI not supported on Android");
@@ -27,6 +27,6 @@ void GUI::set_title(std::string title) {
 GUI::~GUI() {
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 #endif
diff --git a/taichi/ui/gui/cocoa.cpp b/taichi/ui/gui/cocoa.cpp
index 7cfb8b246f735..955fafb123863 100644
--- a/taichi/ui/gui/cocoa.cpp
+++ b/taichi/ui/gui/cocoa.cpp
@@ -271,7 +271,7 @@ __attribute__((constructor)) static void initView() {
   objc_registerClassPair(AppDelClass);
 }
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void GUI::create_window() {
   clscall("NSApplication", "sharedApplication");
@@ -431,6 +431,6 @@ GUI::~GUI() {
   }
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 #endif
diff --git a/taichi/ui/gui/gui.cpp b/taichi/ui/gui/gui.cpp
index fbdf0530be8b6..eebf3674eb312 100644
--- a/taichi/ui/gui/gui.cpp
+++ b/taichi/ui/gui/gui.cpp
@@ -1,6 +1,6 @@
 #include "taichi/ui/gui/gui.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 Vector2 Canvas::Line::vertices[128];
 
@@ -132,4 +132,4 @@ void Canvas::triangle_single(real x0,
   triangle(a, b, c, color);
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/ui/gui/gui.h b/taichi/ui/gui/gui.h
index 7178dbb53709f..5d656bb5df4cf 100644
--- a/taichi/ui/gui/gui.h
+++ b/taichi/ui/gui/gui.h
@@ -27,7 +27,7 @@
 #include <objc/objc.h>
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 TI_FORCE_INLINE Vector4 color_from_hex(uint32 c) {
   return Vector4(c / 65536, c / 256 % 256, c % 256, 255) * (1 / 255.0_f);
@@ -945,4 +945,4 @@ class TI_DLL_EXPORT GUI : public GUIBase {
   ~GUI();
 };
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/ui/gui/win32.cpp b/taichi/ui/gui/win32.cpp
index 2fdd1a896dd22..2d4b3e4b47c2b 100644
--- a/taichi/ui/gui/win32.cpp
+++ b/taichi/ui/gui/win32.cpp
@@ -147,7 +147,7 @@ LRESULT CALLBACK WindowProc(HWND hwnd,
   return DefWindowProc(hwnd, uMsg, wParam, lParam);
 }
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void GUI::process_event() {
   MSG msg;
@@ -330,6 +330,6 @@ GUI::~GUI() {
   }
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 #endif
diff --git a/taichi/ui/gui/x11.cpp b/taichi/ui/gui/x11.cpp
index 5ef4a0ec9429e..458f893fe3c9e 100644
--- a/taichi/ui/gui/x11.cpp
+++ b/taichi/ui/gui/x11.cpp
@@ -14,7 +14,7 @@
 #undef Success
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class CXImage {
  public:
@@ -202,6 +202,6 @@ GUI::~GUI() {
   }
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
 
 #endif
diff --git a/taichi/util/action_recorder.cpp b/taichi/util/action_recorder.cpp
index 8827d2fc719c9..4e78bd948a42b 100644
--- a/taichi/util/action_recorder.cpp
+++ b/taichi/util/action_recorder.cpp
@@ -1,7 +1,7 @@
 #include "taichi/util/action_recorder.h"
 #include "taichi/util/str.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 void ActionArg::serialize(std::ostream &ss) const {
   ss << key << ": ";
@@ -53,4 +53,4 @@ void ActionRecorder::record(const std::string &content,
   ofs_.flush();
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/base64.h b/taichi/util/base64.h
index 7403e681b0f5a..31869d4f2ddb9 100644
--- a/taichi/util/base64.h
+++ b/taichi/util/base64.h
@@ -1,6 +1,6 @@
 #include "taichi/common/core.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 /*
    base64.cpp and base64.h
 
@@ -129,4 +129,4 @@ inline std::string base64_decode(std::string const &encoded_string) {
   return ret;
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/bit.cpp b/taichi/util/bit.cpp
index 026fcfe8f856b..2d183b4c32b24 100644
--- a/taichi/util/bit.cpp
+++ b/taichi/util/bit.cpp
@@ -6,7 +6,7 @@
 #include "taichi/util/testing.h"
 #include "taichi/util/bit.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 namespace bit {
 
@@ -245,4 +245,4 @@ TI_TEST("bit") {
   // TI_P(std::get<1>(e));
   // CHECK(t == compress(std::get<0>(e), std::get<1>(e)));
 }
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/environ_config.h b/taichi/util/environ_config.h
index 9a4aae477eab4..6a349aa616ce6 100644
--- a/taichi/util/environ_config.h
+++ b/taichi/util/environ_config.h
@@ -5,7 +5,7 @@
 #include <string>
 #include <cstdlib>
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 static inline int get_environ_config(const std::string &name,
                                      int default_value = 0) {
@@ -15,4 +15,4 @@ static inline int get_environ_config(const std::string &name,
   return std::stoi(res);
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/util/file_sequence_writer.h b/taichi/util/file_sequence_writer.h
index 2c66cb9771479..63ebd982720fb 100644
--- a/taichi/util/file_sequence_writer.h
+++ b/taichi/util/file_sequence_writer.h
@@ -5,11 +5,9 @@
 #include "taichi/runtime/llvm/llvm_fwd.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 class IRNode;
-}
-}  // namespace taichi
+}  // namespace taichi::lang
 
 namespace taichi {
 
diff --git a/taichi/util/image_buffer.cpp b/taichi/util/image_buffer.cpp
index 9d4dde18bef0b..b76a8c2d4d777 100644
--- a/taichi/util/image_buffer.cpp
+++ b/taichi/util/image_buffer.cpp
@@ -15,7 +15,7 @@
 #define STB_TRUETYPE_IMPLEMENTATION
 #include "stb_truetype.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 template <typename T>
 void Array2D<T>::load_image(const std::string &filename, bool linearize) {
@@ -213,4 +213,4 @@ void write_pgm(Array2D<real> img, const std::string &fn) {
   }
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/io.h b/taichi/util/io.h
index 6409dbf2cd2bf..333865fa7170e 100644
--- a/taichi/util/io.h
+++ b/taichi/util/io.h
@@ -21,7 +21,7 @@
 #include <sys/stat.h>
 #endif
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 inline bool path_exists(const std::string &dir) {
   struct stat buffer;
@@ -149,4 +149,4 @@ bool read_vector_from_disk(std::vector<T> *p_vec, std::string fn) {
   return true;
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/lang_util.cpp b/taichi/util/lang_util.cpp
index 22c38df2d61ec..038e65f58d144 100644
--- a/taichi/util/lang_util.cpp
+++ b/taichi/util/lang_util.cpp
@@ -8,9 +8,7 @@
 #include "taichi/program/compile_config.h"
 #include "taichi/system/timer.h"
 
-TI_NAMESPACE_BEGIN
-
-namespace lang {
+namespace taichi::lang {
 
 CompileConfig default_compile_config;
 std::string compiled_lib_dir;
@@ -102,8 +100,8 @@ bool command_exist(const std::string &command) {
 #endif
 }
 
-}  // namespace lang
-
+}  // namespace taichi::lang
+namespace taichi {
 void initialize_benchmark() {
   // CoreState::set_trigger_gdb_when_crash(true);
   lang::get_cpu_frequency();
@@ -121,4 +119,4 @@ void initialize_benchmark() {
 #endif
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/lang_util.h b/taichi/util/lang_util.h
index 020f5fa8eb0be..4a361d19d39d8 100644
--- a/taichi/util/lang_util.h
+++ b/taichi/util/lang_util.h
@@ -10,7 +10,7 @@
 #include "taichi/ir/type_utils.h"
 #include "taichi/ir/type_factory.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 real get_cpu_frequency();
 
@@ -65,9 +65,9 @@ std::string runtime_lib_dir();
 
 bool command_exist(const std::string &command);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 void initialize_benchmark();
 
 template <typename T, typename... Args, typename FP = T (*)(Args...)>
@@ -84,4 +84,4 @@ template <typename T>
 using function_pointer_type =
     decltype(function_pointer_helper(std::declval<T>()));
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/line_appender.h b/taichi/util/line_appender.h
index 026969a4df4a2..6318481ee8a5d 100644
--- a/taichi/util/line_appender.h
+++ b/taichi/util/line_appender.h
@@ -5,7 +5,7 @@
 #include "spdlog/spdlog.h"
 #include "taichi/common/core.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 class LineAppender {
  public:
@@ -74,4 +74,4 @@ class ScopedIndent {
   LineAppender &la_;
 };
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/offline_cache.h b/taichi/util/offline_cache.h
index ff760de1996a9..80112794eebbd 100644
--- a/taichi/util/offline_cache.h
+++ b/taichi/util/offline_cache.h
@@ -13,8 +13,7 @@
 #include "taichi/util/io.h"
 #include "taichi/util/lock.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace offline_cache {
 
 using Version = std::uint16_t[3];  // {MAJOR, MINOR, PATCH}
@@ -287,5 +286,4 @@ class CacheCleaner {
 };
 
 }  // namespace offline_cache
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/taichi/util/short_name.cpp b/taichi/util/short_name.cpp
index 3a0a334732a0b..96ddc8d7825b6 100644
--- a/taichi/util/short_name.cpp
+++ b/taichi/util/short_name.cpp
@@ -1,7 +1,7 @@
 #include "short_name.h"
 #include "base64.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 namespace {
 const std::string alphatable =
     "ABCDEFGHIJKLMNOPQRSTUVWXYZ";  // e.g. `if` is not a good var name, but `If`
@@ -20,4 +20,4 @@ std::string make_short_name_by_id(int id) {
   std::reverse(res.begin(), res.end());
   return res;
 }
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/short_name.h b/taichi/util/short_name.h
index 8b9b102403171..dbe57ee05aa3d 100644
--- a/taichi/util/short_name.h
+++ b/taichi/util/short_name.h
@@ -3,8 +3,8 @@
 #include <string>
 #include "taichi/common/core.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 std::string make_short_name_by_id(int id);
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/statistics.cpp b/taichi/util/statistics.cpp
index d50bbe40e21fa..d418024fa6adc 100644
--- a/taichi/util/statistics.cpp
+++ b/taichi/util/statistics.cpp
@@ -1,6 +1,6 @@
 #include "statistics.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 Statistics stat;
 
@@ -30,4 +30,4 @@ void Statistics::clear() {
   counters_.clear();
 }
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/taichi/util/str.cpp b/taichi/util/str.cpp
index 469bcf255dadd..7dc822c6f7627 100644
--- a/taichi/util/str.cpp
+++ b/taichi/util/str.cpp
@@ -4,7 +4,7 @@
 
 #include "taichi/inc/constants.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 std::string c_quoted(std::string const &str) {
   // https://zh.cppreference.com/w/cpp/language/escape
@@ -60,4 +60,4 @@ std::string format_error_message(const std::string &error_message_template,
   return error_message_formatted;
 }
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/util/str.h b/taichi/util/str.h
index d703a94a92f0e..3db6172996a42 100644
--- a/taichi/util/str.h
+++ b/taichi/util/str.h
@@ -7,7 +7,7 @@
 
 #include "taichi/util/lang_util.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Quote |str| with a pair of ". Escape special characters like \n, \t etc.
 std::string c_quoted(std::string const &str);
@@ -15,4 +15,4 @@ std::string c_quoted(std::string const &str);
 std::string format_error_message(const std::string &error_message_template,
                                  const std::function<uint64(int)> &fetcher);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/taichi/util/zip.cpp b/taichi/util/zip.cpp
index f95312d6cc187..b6e3fd5a688e6 100644
--- a/taichi/util/zip.cpp
+++ b/taichi/util/zip.cpp
@@ -13,7 +13,7 @@
 
 #include "miniz.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 namespace zip {
 
@@ -112,4 +112,4 @@ std::vector<uint8> read(const std::string fn, bool verbose) {
 
 }  // namespace zip
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/tests/cpp/analysis/alias_analysis_test.cpp b/tests/cpp/analysis/alias_analysis_test.cpp
index ac6dfd4492b90..c4c2bfb6b1930 100644
--- a/tests/cpp/analysis/alias_analysis_test.cpp
+++ b/tests/cpp/analysis/alias_analysis_test.cpp
@@ -8,8 +8,7 @@
 #include "taichi/ir/snode.h"
 #include "taichi/ir/statements.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace irpass {
 namespace analysis {
 namespace {
@@ -148,5 +147,4 @@ TEST(AliasAnalysis, ExternalPtr_DiffPtr) {
 
 }  // namespace analysis
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/analysis/bls_analyzer_test.cpp b/tests/cpp/analysis/bls_analyzer_test.cpp
index 4ebc601116f0c..205617df3b97e 100644
--- a/tests/cpp/analysis/bls_analyzer_test.cpp
+++ b/tests/cpp/analysis/bls_analyzer_test.cpp
@@ -10,8 +10,7 @@
 #include "taichi/struct/struct.h"
 #include "tests/cpp/struct/fake_struct_compiler.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 constexpr int kBlockSize = 8;
@@ -144,5 +143,4 @@ TEST_F(BLSAnalyzerTest, Shl) {
 }
 
 }  // namespace
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/analysis/same_statements_test.cpp b/tests/cpp/analysis/same_statements_test.cpp
index 41fba37561f36..9796e51eb46c2 100644
--- a/tests/cpp/analysis/same_statements_test.cpp
+++ b/tests/cpp/analysis/same_statements_test.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/analysis.h"
 #include "taichi/ir/statements.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(SameStatements, TestSameBlock) {
   auto block = std::make_unique<Block>();
@@ -168,5 +167,4 @@ TEST(SameStatements, TestSameLoopIndex) {
   EXPECT_TRUE(irpass::analysis::same_value(loop_index_a, loop_index_b));
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/analysis/value_diff_test.cpp b/tests/cpp/analysis/value_diff_test.cpp
index 5962ec0012556..8a2f92ce9d54b 100644
--- a/tests/cpp/analysis/value_diff_test.cpp
+++ b/tests/cpp/analysis/value_diff_test.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/ir_builder.h"
 #include "taichi/ir/statements.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace irpass {
 namespace analysis {
 
@@ -132,5 +131,4 @@ TEST(DiffRangeTest, Shl) {
 
 }  // namespace analysis
 }  // namespace irpass
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/aot/gfx_utils.cpp b/tests/cpp/aot/gfx_utils.cpp
index 301c81879b8b5..1c68f3f55be8f 100644
--- a/tests/cpp/aot/gfx_utils.cpp
+++ b/tests/cpp/aot/gfx_utils.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/runtime/gfx/aot_module_loader_impl.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace aot_test_utils {
 static void write_devalloc(taichi::lang::DeviceAllocation &alloc,
                            const void *data,
@@ -475,5 +474,4 @@ void run_mpm88_graph(Arch arch, taichi::lang::Device *device_) {
   device_->dealloc_memory(devalloc_pos);
 }
 }  // namespace aot_test_utils
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/aot/gfx_utils.h b/tests/cpp/aot/gfx_utils.h
index 1a6e90c75abe4..02bcc1abf0726 100644
--- a/tests/cpp/aot/gfx_utils.h
+++ b/tests/cpp/aot/gfx_utils.h
@@ -6,8 +6,7 @@
 #include "taichi/program/graph_builder.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace aot_test_utils {
 [[maybe_unused]] static void write_devalloc(
     taichi::lang::DeviceAllocation &alloc,
@@ -32,5 +31,4 @@ void view_devalloc_as_ndarray(Device *device_);
 
 [[maybe_unused]] void run_mpm88_graph(Arch arch, taichi::lang::Device *device_);
 }  // namespace aot_test_utils
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/aot/llvm/bitmasked_aot_test.cpp b/tests/cpp/aot/llvm/bitmasked_aot_test.cpp
index 6041f5d1cff82..64252c4706d63 100644
--- a/tests/cpp/aot/llvm/bitmasked_aot_test.cpp
+++ b/tests/cpp/aot/llvm/bitmasked_aot_test.cpp
@@ -13,8 +13,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 static void run_bitmasked_tests(aot::Module *mod,
                                 LlvmRuntimeExecutor *exec,
@@ -111,5 +110,4 @@ TEST(LlvmAotTest, CudaBitmasked) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/aot/llvm/dynamic_aot_test.cpp b/tests/cpp/aot/llvm/dynamic_aot_test.cpp
index f047eb75aa6af..92f6a24927934 100644
--- a/tests/cpp/aot/llvm/dynamic_aot_test.cpp
+++ b/tests/cpp/aot/llvm/dynamic_aot_test.cpp
@@ -13,8 +13,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 static void run_dynamic_tests(aot::Module *mod,
                               LlvmRuntimeExecutor *exec,
@@ -111,5 +110,4 @@ TEST(LlvmAotTest, CudaDynamic) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/aot/llvm/field_aot_test.cpp b/tests/cpp/aot/llvm/field_aot_test.cpp
index 34a801e786a22..5a93b23d82e71 100644
--- a/tests/cpp/aot/llvm/field_aot_test.cpp
+++ b/tests/cpp/aot/llvm/field_aot_test.cpp
@@ -13,8 +13,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 static void run_field_tests(aot::Module *mod,
                             LlvmRuntimeExecutor *exec,
@@ -143,5 +142,4 @@ TEST(LlvmAotTest, CudaField) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/aot/llvm/field_cgraph_test.cpp b/tests/cpp/aot/llvm/field_cgraph_test.cpp
index d11ce02055b72..71f103b881c9a 100644
--- a/tests/cpp/aot/llvm/field_cgraph_test.cpp
+++ b/tests/cpp/aot/llvm/field_cgraph_test.cpp
@@ -13,8 +13,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 void run_graph_tests(aot::Module *mod,
                      LlvmRuntimeExecutor *exec,
@@ -89,5 +88,4 @@ TEST(LlvmCGraph, CudaField) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/aot/llvm/kernel_aot_test.cpp b/tests/cpp/aot/llvm/kernel_aot_test.cpp
index d0783938f98ab..bb177dfd37aa9 100644
--- a/tests/cpp/aot/llvm/kernel_aot_test.cpp
+++ b/tests/cpp/aot/llvm/kernel_aot_test.cpp
@@ -12,8 +12,7 @@
 #include "taichi/program/context.h"
 #undef TI_RUNTIME_HOST
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(LlvmAotTest, CpuKernel) {
   CompileConfig cfg;
@@ -102,5 +101,4 @@ TEST(LlvmAotTest, CudaKernel) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/backends/dx11_device_test.cpp b/tests/cpp/backends/dx11_device_test.cpp
index f1c878030aabf..3d97c0d5d6952 100644
--- a/tests/cpp/backends/dx11_device_test.cpp
+++ b/tests/cpp/backends/dx11_device_test.cpp
@@ -9,8 +9,7 @@
 #include "taichi/system/memory_pool.h"
 #include "tests/cpp/program/test_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace directx11 {
 
 TEST(Dx11DeviceCreationTest, CreateDeviceAndAllocateMemory) {
@@ -153,7 +152,6 @@ TEST(Dx11ProgramTest, MaterializeRuntimeTest) {
 }
 
 }  // namespace directx11
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif
diff --git a/tests/cpp/codegen/refine_coordinates_test.cpp b/tests/cpp/codegen/refine_coordinates_test.cpp
index 8812ec64a6e4f..f776f444fb819 100644
--- a/tests/cpp/codegen/refine_coordinates_test.cpp
+++ b/tests/cpp/codegen/refine_coordinates_test.cpp
@@ -16,9 +16,7 @@
 #include "taichi/runtime/program_impls/llvm/llvm_program.h"
 #include "taichi/codegen/llvm/struct_llvm.h"
 
-namespace taichi {
-
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 constexpr char kFuncName[] = "run_refine_coords";
@@ -183,6 +181,5 @@ TEST_F(RefineCoordinatesTest, Basic) {
 }
 
 }  // namespace
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 #endif  // #ifdef TI_WITH_LLVM
diff --git a/tests/cpp/common/dict_test.cpp b/tests/cpp/common/dict_test.cpp
index 94d4e8e7d4003..0bd167be5d937 100644
--- a/tests/cpp/common/dict_test.cpp
+++ b/tests/cpp/common/dict_test.cpp
@@ -7,8 +7,7 @@
 #include "taichi/common/dict.h"
 #include "taichi/util/testing.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(Dict, Config) {
   Dict dict;
@@ -32,5 +31,4 @@ TEST(Dict, Config) {
   EXPECT_EQ(dict.get<std::string>("str"), "Hello");
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/common/serialization_test.cpp b/tests/cpp/common/serialization_test.cpp
index 5e049ee42cbab..373bb7420ec17 100644
--- a/tests/cpp/common/serialization_test.cpp
+++ b/tests/cpp/common/serialization_test.cpp
@@ -5,8 +5,7 @@
 #include "gtest/gtest.h"
 #include "taichi/common/core.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 class BinIoPair {
@@ -146,5 +145,4 @@ TEST(Serialization, MoveOnly) {
 }
 
 }  // namespace
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/frontend_type_inference_test.cpp b/tests/cpp/ir/frontend_type_inference_test.cpp
index 3798bd7345428..19c87dbc8877d 100644
--- a/tests/cpp/ir/frontend_type_inference_test.cpp
+++ b/tests/cpp/ir/frontend_type_inference_test.cpp
@@ -5,8 +5,7 @@
 #include "taichi/ir/expression_ops.h"
 #include "taichi/program/compile_config.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(FrontendTypeInference, Const) {
   auto const_i64 = value<int64>(1LL << 63);
@@ -183,5 +182,4 @@ TEST(FrontendTypeInference, InternalFuncCall) {
   EXPECT_EQ(internal_func_call->ret_type, PrimitiveType::i32);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/ir_builder_test.cpp b/tests/cpp/ir/ir_builder_test.cpp
index cf681a3c99eb9..4edf8a446b7e3 100644
--- a/tests/cpp/ir/ir_builder_test.cpp
+++ b/tests/cpp/ir/ir_builder_test.cpp
@@ -8,8 +8,7 @@
 #include "taichi/rhi/vulkan/vulkan_loader.h"
 #endif
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(IRBuilder, Basic) {
   IRBuilder builder;
@@ -154,5 +153,4 @@ TEST(IRBuilder, Ndarray) {
   EXPECT_EQ(array.read_int({1}), 3);
   EXPECT_EQ(array.read_int({2}), 42);
 }
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/ir_test.cpp b/tests/cpp/ir/ir_test.cpp
index 09f5bb6305ce0..7961d07538dda 100644
--- a/tests/cpp/ir/ir_test.cpp
+++ b/tests/cpp/ir/ir_test.cpp
@@ -3,8 +3,7 @@
 #include "taichi/ir/ir.h"
 #include "taichi/ir/statements.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 std::unique_ptr<ConstStmt> make_const_i32(int32_t value) {
@@ -43,5 +42,4 @@ TEST(Block, EraseRange) {
 }
 
 }  // namespace
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/ir_type_promotion_test.cpp b/tests/cpp/ir/ir_type_promotion_test.cpp
index b4b71b5044092..afb51b9c43a81 100644
--- a/tests/cpp/ir/ir_type_promotion_test.cpp
+++ b/tests/cpp/ir/ir_type_promotion_test.cpp
@@ -5,8 +5,7 @@
 #include "taichi/ir/transforms.h"
 #include "tests/cpp/program/test_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(IRTypePromotionTest, ShiftOp) {
   IRBuilder builder;
@@ -27,5 +26,4 @@ TEST(IRTypePromotionTest, ShiftOp) {
   EXPECT_TRUE(ret_type->is_primitive(PrimitiveTypeID::u8));
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/ndarray_kernel.cpp b/tests/cpp/ir/ndarray_kernel.cpp
index 080d097b1fd27..e4148d94fb278 100644
--- a/tests/cpp/ir/ndarray_kernel.cpp
+++ b/tests/cpp/ir/ndarray_kernel.cpp
@@ -1,7 +1,6 @@
 #include "tests/cpp/ir/ndarray_kernel.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 std::unique_ptr<Kernel> setup_kernel1(Program *prog) {
   IRBuilder builder1;
@@ -44,5 +43,4 @@ std::unique_ptr<Kernel> setup_kernel2(Program *prog) {
   ker2->insert_scalar_arg(get_data_type<int>());
   return ker2;
 }
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/ndarray_kernel.h b/tests/cpp/ir/ndarray_kernel.h
index 9ee8d32159615..69b25c59027b2 100644
--- a/tests/cpp/ir/ndarray_kernel.h
+++ b/tests/cpp/ir/ndarray_kernel.h
@@ -4,11 +4,9 @@
 #include "taichi/inc/constants.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 std::unique_ptr<Kernel> setup_kernel1(Program *prog);
 
 std::unique_ptr<Kernel> setup_kernel2(Program *prog);
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/stmt_field_manager_test.cpp b/tests/cpp/ir/stmt_field_manager_test.cpp
index 0384beb02c740..6bce1ccf8a155 100644
--- a/tests/cpp/ir/stmt_field_manager_test.cpp
+++ b/tests/cpp/ir/stmt_field_manager_test.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/statements.h"
 #include "taichi/util/testing.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 class TestStmt : public Stmt {
@@ -74,5 +73,4 @@ TEST(StmtFieldManager, TestStmtFieldManagerWithVector) {
   EXPECT_EQ(a->field_manager.equal(c->field_manager), false);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/ir/type_test.cpp b/tests/cpp/ir/type_test.cpp
index f14aaacd7f524..aec036384a54d 100644
--- a/tests/cpp/ir/type_test.cpp
+++ b/tests/cpp/ir/type_test.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/ir/type_factory.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(Type, TypeToString) {
   auto f16 = TypeFactory::get_instance().get_primitive_real_type(16);
@@ -45,5 +44,4 @@ TEST(Type, TypeToString) {
   EXPECT_EQ(qa->to_string(), "qa(qi1x32)");
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/llvm/llvm_offline_cache_test.cpp b/tests/cpp/llvm/llvm_offline_cache_test.cpp
index 8572ea4dd13f9..7b1cf34f4468c 100644
--- a/tests/cpp/llvm/llvm_offline_cache_test.cpp
+++ b/tests/cpp/llvm/llvm_offline_cache_test.cpp
@@ -28,8 +28,7 @@ namespace fs = std::experimental::filesystem;
 #include "taichi/program/compile_config.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 constexpr char kKernelName[] = "foo";
@@ -148,8 +147,7 @@ INSTANTIATE_TEST_SUITE_P(Format,
                          testing::Values(Format::LL, Format::BC));
 
 }  // namespace
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
 
 #endif  // #if defined(TI_PLATFORM_LINUX) || defined(TI_PLATFORM_WINDOWS)
 #endif  // #ifdef TI_WITH_LLVM
diff --git a/tests/cpp/offline_cache/load_metadata_test.cpp b/tests/cpp/offline_cache/load_metadata_test.cpp
index 9db7d7de92d9a..406b3ae8c9eb3 100644
--- a/tests/cpp/offline_cache/load_metadata_test.cpp
+++ b/tests/cpp/offline_cache/load_metadata_test.cpp
@@ -6,8 +6,7 @@
 #include "taichi/runtime/llvm/llvm_offline_cache.h"
 #endif  // TI_WITH_LLVM
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 namespace {
 
@@ -108,5 +107,4 @@ TEST(OfflineCache, LoadMetadata) {
   load_metadata_test<oc::Metadata>();
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/program/test_program.cpp b/tests/cpp/program/test_program.cpp
index c08eb254ee02a..96e1723be780a 100644
--- a/tests/cpp/program/test_program.cpp
+++ b/tests/cpp/program/test_program.cpp
@@ -1,7 +1,6 @@
 #include "tests/cpp/program/test_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 void TestProgram::setup(Arch arch) {
   prog_ = std::make_unique<Program>(arch);
@@ -10,5 +9,4 @@ void TestProgram::setup(Arch arch) {
                         /*compile_only=*/false);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/program/test_program.h b/tests/cpp/program/test_program.h
index d9c2237f6b988..26df5001e25aa 100644
--- a/tests/cpp/program/test_program.h
+++ b/tests/cpp/program/test_program.h
@@ -4,8 +4,7 @@
 
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class TestProgram {
  public:
@@ -19,5 +18,4 @@ class TestProgram {
   std::unique_ptr<Program> prog_{nullptr};
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/struct/fake_struct_compiler.h b/tests/cpp/struct/fake_struct_compiler.h
index dd632c0ef576a..c4e9f9ea52d55 100644
--- a/tests/cpp/struct/fake_struct_compiler.h
+++ b/tests/cpp/struct/fake_struct_compiler.h
@@ -1,7 +1,6 @@
 #include "taichi/struct/struct.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class FakeStructCompiler : public StructCompiler {
  public:
@@ -15,5 +14,4 @@ class FakeStructCompiler : public StructCompiler {
   }
 };
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/struct/snode_tree_test.cpp b/tests/cpp/struct/snode_tree_test.cpp
index 5414dbde56fe3..ceec825bd5c32 100644
--- a/tests/cpp/struct/snode_tree_test.cpp
+++ b/tests/cpp/struct/snode_tree_test.cpp
@@ -2,8 +2,7 @@
 
 #include "taichi/struct/snode_tree.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 TEST(SNodeTree, GetSNodeToRootMapping) {
   constexpr int kSNodeSize = 16;
@@ -27,5 +26,4 @@ TEST(SNodeTree, GetSNodeToRootMapping) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/task/test_exception_handling.cpp b/tests/cpp/task/test_exception_handling.cpp
index bc185429628e7..c5226313119f8 100644
--- a/tests/cpp/task/test_exception_handling.cpp
+++ b/tests/cpp/task/test_exception_handling.cpp
@@ -2,7 +2,7 @@
 #include "taichi/ir/ir.h"
 #include "taichi/ir/statements.h"
 
-TLANG_NAMESPACE_BEGIN
+namespace taichi::lang {
 
 // Simulate the AST transforms on the Google Colab Ubuntu kernels to see why it
 // crashes
@@ -99,4 +99,4 @@ auto test_exception_handling_auto = []() {
 TI_REGISTER_TASK(test_exception_handling);
 TI_REGISTER_TASK(test_exception_handling_auto);
 
-TLANG_NAMESPACE_END
+}  // namespace taichi::lang
diff --git a/tests/cpp/task/test_gui.cpp b/tests/cpp/task/test_gui.cpp
index 4b68cc31d6196..332f43b8c89f5 100644
--- a/tests/cpp/task/test_gui.cpp
+++ b/tests/cpp/task/test_gui.cpp
@@ -3,7 +3,7 @@
 #include "taichi/gui/gui.h"
 #include "taichi/common/task.h"
 
-TI_NAMESPACE_BEGIN
+namespace taichi {
 
 auto test_gui = []() {
   // GUI gui("GUI Test", 1000, 400, false);
@@ -47,4 +47,4 @@ auto test_gui = []() {
 
 TI_REGISTER_TASK(test_gui);
 
-TI_NAMESPACE_END
+}  // namespace taichi
diff --git a/tests/cpp/transforms/alg_simp_test.cpp b/tests/cpp/transforms/alg_simp_test.cpp
index 6857f84969719..50fb41f77b840 100644
--- a/tests/cpp/transforms/alg_simp_test.cpp
+++ b/tests/cpp/transforms/alg_simp_test.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/transforms.h"
 #include "tests/cpp/program/test_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class AlgebraicSimplicationTest : public ::testing::Test {
  protected:
@@ -173,5 +172,4 @@ TEST_F(AlgebraicSimplicationTest, SimplifyAndMinusOne) {
   EXPECT_TRUE((*block)[0]->is<GlobalTemporaryStmt>());
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/binary_op_simplify_test.cpp b/tests/cpp/transforms/binary_op_simplify_test.cpp
index f6cdd8743a47b..d7e1463524ed1 100644
--- a/tests/cpp/transforms/binary_op_simplify_test.cpp
+++ b/tests/cpp/transforms/binary_op_simplify_test.cpp
@@ -5,8 +5,7 @@
 #include "taichi/ir/transforms.h"
 #include "tests/cpp/program/test_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class BinaryOpSimplifyTest : public ::testing::Test {
  protected:
@@ -101,5 +100,4 @@ TEST_F(BinaryOpSimplifyTest, ModPOT) {
   EXPECT_EQ(ir_block->statements[3]->as<ReturnStmt>()->values[0], bin_op);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/determine_ad_stack_size_test.cpp b/tests/cpp/transforms/determine_ad_stack_size_test.cpp
index eb26da430c3d8..a2dcbcd1e4b1e 100644
--- a/tests/cpp/transforms/determine_ad_stack_size_test.cpp
+++ b/tests/cpp/transforms/determine_ad_stack_size_test.cpp
@@ -6,8 +6,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class DetermineAdStackSizeTest
     : public ::testing::TestWithParam<std::tuple<int, int>> {
@@ -184,5 +183,4 @@ TEST_F(DetermineAdStackSizeTest, EmptyNodes) {
   EXPECT_EQ(stack->max_size, 2);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/extract_constant_test.cpp b/tests/cpp/transforms/extract_constant_test.cpp
index bee205bf5ef18..9d93adebf7471 100644
--- a/tests/cpp/transforms/extract_constant_test.cpp
+++ b/tests/cpp/transforms/extract_constant_test.cpp
@@ -6,8 +6,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class ExtractConstantTest : public ::testing::Test {
  protected:
@@ -59,5 +58,4 @@ TEST_F(ExtractConstantTest, ExtractConstant) {
   EXPECT_EQ(ir_block->size(), 4);
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/inlining_test.cpp b/tests/cpp/transforms/inlining_test.cpp
index 8c73fe065d1cc..02de40d543189 100644
--- a/tests/cpp/transforms/inlining_test.cpp
+++ b/tests/cpp/transforms/inlining_test.cpp
@@ -6,8 +6,7 @@
 #include "taichi/ir/transforms.h"
 #include "taichi/program/program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 class InliningTest : public ::testing::Test {
  protected:
@@ -58,5 +57,4 @@ TEST_F(InliningTest, ArgLoadOfArgLoad) {
   EXPECT_TRUE(irpass::analysis::same_statements(func_block, kernel_block));
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/make_block_local_test.cpp b/tests/cpp/transforms/make_block_local_test.cpp
index a4094beb8cd8e..c38a80f4916c2 100644
--- a/tests/cpp/transforms/make_block_local_test.cpp
+++ b/tests/cpp/transforms/make_block_local_test.cpp
@@ -9,8 +9,7 @@
 #include "taichi/struct/struct.h"
 #include "tests/cpp/struct/fake_struct_compiler.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 class MakeBlockLocalTest : public ::testing::Test {
@@ -192,5 +191,4 @@ TEST_F(MakeBlockLocalTest, Basic) {
 }
 
 }  // namespace
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/scalar_pointer_lowerer_test.cpp b/tests/cpp/transforms/scalar_pointer_lowerer_test.cpp
index d8817948d3969..e9e16f0de98fd 100644
--- a/tests/cpp/transforms/scalar_pointer_lowerer_test.cpp
+++ b/tests/cpp/transforms/scalar_pointer_lowerer_test.cpp
@@ -10,8 +10,7 @@
 #include "taichi/transforms/scalar_pointer_lowerer.h"
 #include "tests/cpp/struct/fake_struct_compiler.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 namespace {
 
 constexpr int kPointerSize = 4;
@@ -105,5 +104,4 @@ TEST_F(ScalarPointerLowererTest, Basic) {
 }
 
 }  // namespace
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/scalarize_test.cpp b/tests/cpp/transforms/scalarize_test.cpp
index ab373492f6c0d..27be6b773f7a6 100644
--- a/tests/cpp/transforms/scalarize_test.cpp
+++ b/tests/cpp/transforms/scalarize_test.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/transforms.h"
 #include "tests/cpp/program/test_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // Basic tests within a basic block
 template <typename T>
@@ -141,5 +140,4 @@ TEST(Scalarize, ScalarizeLoad) {
   test_load_scalarize<LocalLoadStmt>();
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang
diff --git a/tests/cpp/transforms/simplify_test.cpp b/tests/cpp/transforms/simplify_test.cpp
index 6ead8b6e33d7f..c914c6311bd27 100644
--- a/tests/cpp/transforms/simplify_test.cpp
+++ b/tests/cpp/transforms/simplify_test.cpp
@@ -4,8 +4,7 @@
 #include "taichi/ir/transforms.h"
 #include "tests/cpp/program/test_program.h"
 
-namespace taichi {
-namespace lang {
+namespace taichi::lang {
 
 // Basic tests within a basic block
 
@@ -54,5 +53,4 @@ TEST(Simplify, SimplifyLinearizedWithTrivialInputs) {
   }
 }
 
-}  // namespace lang
-}  // namespace taichi
+}  // namespace taichi::lang