diff --git a/dora/src/cannon/codegen.rs b/dora/src/cannon/codegen.rs
index a5404e2c..7fd6e41a 100644
--- a/dora/src/cannon/codegen.rs
+++ b/dora/src/cannon/codegen.rs
@@ -31,8 +31,8 @@ use crate::vm::{
     get_concrete_tuple_array, get_concrete_tuple_bytecode_ty, get_concrete_tuple_ty,
     specialize_class_id_params, specialize_enum_class, specialize_enum_id_params,
     specialize_lambda, specialize_trait_object, specialize_tuple_array, specialize_tuple_bty,
-    specialize_tuple_ty, specialize_type, specialize_type_list, specialize_value_id_params,
-    EnumLayout, GcPoint, LazyCompilationSite, Trap, VM,
+    specialize_tuple_ty, specialize_type, specialize_type_list, value_instance, EnumLayout,
+    GcPoint, LazyCompilationSite, Trap, VM,
 };
 use crate::vtable::VTable;
 
@@ -230,10 +230,7 @@ impl<'a> CannonCodeGen<'a> {
 
                 BytecodeType::Value(value_id, type_params) => {
                     let offset = self.register_offset(Register(idx));
-                    let value_instance_id =
-                        specialize_value_id_params(self.vm, value_id, type_params);
-                    let value_instance = self.vm.value_instances.idx(value_instance_id);
-
+                    let value_instance = value_instance(self.vm, value_id, type_params);
                     for &ref_offset in &value_instance.ref_fields {
                         self.references.push(offset + ref_offset);
                     }
@@ -1311,9 +1308,7 @@ impl<'a> CannonCodeGen<'a> {
         dest: RegOrOffset,
         src: RegOrOffset,
     ) {
-        let value_instance_id = specialize_value_id_params(self.vm, value_id, type_params);
-        let value_instance = self.vm.value_instances.idx(value_instance_id);
-
+        let value_instance = value_instance(self.vm, value_id, type_params);
         for field in &value_instance.fields {
             let src = src.offset(field.offset);
             let dest = dest.offset(field.offset);
@@ -1549,9 +1544,7 @@ impl<'a> CannonCodeGen<'a> {
         let type_params = specialize_type_list(self.vm, &type_params, self.type_params);
         debug_assert!(type_params.iter().all(|ty| ty.is_concrete_type(self.vm)));
 
-        let value_instance_id = specialize_value_id_params(self.vm, value_id, type_params.clone());
-        let value_instance = self.vm.value_instances.idx(value_instance_id);
-
+        let value_instance = value_instance(self.vm, value_id, type_params);
         let field = &value_instance.fields[field_id.to_usize()];
 
         let bytecode_type = self.specialize_register_type(dest);
@@ -1661,9 +1654,7 @@ impl<'a> CannonCodeGen<'a> {
                     RegOrOffset::Offset(src_offset),
                 );
 
-                let value_instance_id =
-                    specialize_value_id_params(self.vm, *value_id, type_params.clone());
-                let value_instance = self.vm.value_instances.idx(value_instance_id);
+                let value_instance = value_instance(self.vm, *value_id, type_params.clone());
                 needs_write_barrier = value_instance.contains_references();
             }
 
@@ -2468,9 +2459,7 @@ impl<'a> CannonCodeGen<'a> {
         let type_params = specialize_type_list(self.vm, &type_params, self.type_params);
         debug_assert!(type_params.iter().all(|ty| ty.is_concrete_type(self.vm)));
 
-        let value_instance_id = specialize_value_id_params(self.vm, value_id, type_params);
-        let value_instance = self.vm.value_instances.idx(value_instance_id);
-
+        let value_instance = value_instance(self.vm, value_id, type_params);
         let arguments = self.argument_stack.drain(..).collect::<Vec<_>>();
 
         let dest_offset = self.register_offset(dest);
@@ -2716,9 +2705,7 @@ impl<'a> CannonCodeGen<'a> {
             }
 
             BytecodeType::Value(value_id, type_params) => {
-                let value_instance_id =
-                    specialize_value_id_params(self.vm, value_id, type_params.clone());
-                let value_instance = self.vm.value_instances.idx(value_instance_id);
+                let value_instance = value_instance(self.vm, value_id, type_params.clone());
 
                 self.asm
                     .array_address(REG_TMP1, REG_RESULT, REG_TMP1, value_instance.size);
@@ -2860,10 +2847,7 @@ impl<'a> CannonCodeGen<'a> {
             }
 
             BytecodeType::Value(value_id, type_params) => {
-                let value_instance_id =
-                    specialize_value_id_params(self.vm, value_id, type_params.clone());
-                let value_instance = self.vm.value_instances.idx(value_instance_id);
-
+                let value_instance = value_instance(self.vm, value_id, type_params.clone());
                 let element_size = value_instance.size;
                 self.asm
                     .array_address(REG_TMP1, REG_RESULT, REG_TMP1, element_size);
@@ -5403,10 +5387,7 @@ pub fn size(vm: &VM, ty: BytecodeType) -> i32 {
             }
         }
         BytecodeType::Value(value_id, type_params) => {
-            let vdef_id = specialize_value_id_params(vm, value_id, type_params);
-            let vdef = vm.value_instances.idx(vdef_id);
-
-            vdef.size
+            value_instance(vm, value_id, type_params).size
         }
         BytecodeType::Class(_, _) | BytecodeType::Lambda(_, _) => {
             unreachable!()
diff --git a/dora/src/gc/root.rs b/dora/src/gc/root.rs
index 1c751e92..e1aa146d 100644
--- a/dora/src/gc/root.rs
+++ b/dora/src/gc/root.rs
@@ -5,8 +5,7 @@ use crate::language::ty::SourceType;
 use crate::stack::DoraToNativeInfo;
 use crate::threads::DoraThread;
 use crate::vm::{
-    get_concrete_tuple_ty, specialize_enum_id_params, specialize_value_id_params, CodeKind,
-    EnumLayout, VM,
+    get_concrete_tuple_ty, specialize_enum_id_params, value_instance, CodeKind, EnumLayout, VM,
 };
 
 pub fn determine_strong_roots(vm: &VM, threads: &[Arc<DoraThread>]) -> Vec<Slot> {
@@ -62,10 +61,8 @@ fn iterate_roots_from_globals<F: FnMut(Slot)>(vm: &VM, callback: &mut F) {
 
         match global_var.ty {
             SourceType::Value(value_id, ref type_params) => {
-                let sdef_id = specialize_value_id_params(vm, value_id, type_params.clone());
-                let sdef = vm.value_instances.idx(sdef_id);
-
-                for &offset in &sdef.ref_fields {
+                let value_instance = value_instance(vm, value_id, type_params.clone());
+                for &offset in &value_instance.ref_fields {
                     let slot_address = global_var.address_value.offset(offset as usize);
                     let slot = Slot::at(slot_address);
                     callback(slot);
diff --git a/dora/src/vm.rs b/dora/src/vm.rs
index 747918e8..4703ce54 100644
--- a/dora/src/vm.rs
+++ b/dora/src/vm.rs
@@ -48,7 +48,7 @@ pub use self::specialize::{
     add_ref_fields, replace_type_param, specialize_class_id, specialize_class_id_params,
     specialize_enum_class, specialize_enum_id_params, specialize_lambda, specialize_trait_object,
     specialize_tuple_array, specialize_tuple_bty, specialize_tuple_ty, specialize_type,
-    specialize_type_list, specialize_value_id_params,
+    specialize_type_list, specialize_value_id_params, value_instance,
 };
 pub use self::stubs::{setup_stubs, Stubs};
 pub use self::tuples::{
diff --git a/dora/src/vm/specialize.rs b/dora/src/vm/specialize.rs
index 6ad898f6..d9f8eae7 100644
--- a/dora/src/vm/specialize.rs
+++ b/dora/src/vm/specialize.rs
@@ -42,6 +42,15 @@ pub fn specialize_type_list(
     SourceTypeArray::with(specialized_types)
 }
 
+pub fn value_instance(
+    vm: &VM,
+    value_id: ValueDefinitionId,
+    type_params: SourceTypeArray,
+) -> Arc<ValueInstance> {
+    let value_instance_id = specialize_value_id_params(vm, value_id, type_params);
+    vm.value_instances.idx(value_instance_id)
+}
+
 pub fn specialize_value_id_params(
     vm: &VM,
     value_id: ValueDefinitionId,
@@ -288,10 +297,8 @@ pub fn add_ref_fields(vm: &VM, ref_fields: &mut Vec<i32>, offset: i32, ty: Sourc
             }
         }
     } else if let SourceType::Value(value_id, type_params) = ty.clone() {
-        let sdef_id = specialize_value_id_params(vm, value_id, type_params);
-        let sdef = vm.value_instances.idx(sdef_id);
-
-        for &ref_offset in &sdef.ref_fields {
+        let value_instance = value_instance(vm, value_id, type_params);
+        for &ref_offset in &value_instance.ref_fields {
             ref_fields.push(offset + ref_offset);
         }
     } else if ty.reference_type() {
@@ -419,10 +426,8 @@ fn create_specialized_class_array(
             }
 
             SourceType::Value(value_id, type_params) => {
-                let vdef_id = specialize_value_id_params(vm, value_id, type_params);
-                let vdef = vm.value_instances.idx(vdef_id);
-
-                InstanceSize::ValueArray(vdef.size)
+                let value_instance = value_instance(vm, value_id, type_params);
+                InstanceSize::ValueArray(value_instance.size)
             }
 
             SourceType::Enum(enum_id, type_params) => {
diff --git a/dora/src/vm/ty.rs b/dora/src/vm/ty.rs
index be51f9b1..6b19a1ae 100644
--- a/dora/src/vm/ty.rs
+++ b/dora/src/vm/ty.rs
@@ -1,8 +1,7 @@
 use crate::language::ty::SourceType;
 use crate::mem;
 use crate::mode::MachineMode;
-use crate::vm::{get_concrete_tuple_ty, VM};
-use crate::vm::{specialize_enum_id_params, specialize_value_id_params, EnumLayout};
+use crate::vm::{get_concrete_tuple_ty, specialize_enum_id_params, value_instance, EnumLayout, VM};
 
 impl SourceType {
     pub fn size(&self, vm: &VM) -> i32 {
@@ -30,10 +29,8 @@ impl SourceType {
             SourceType::Class(_, _) | SourceType::Lambda(_, _) | SourceType::Ptr => {
                 mem::ptr_width()
             }
-            SourceType::Value(value_id, params) => {
-                let value_instance_id = specialize_value_id_params(vm, *value_id, params.clone());
-                let value_instance = vm.value_instances.idx(value_instance_id);
-
+            SourceType::Value(value_id, type_params) => {
+                let value_instance = value_instance(vm, *value_id, type_params.clone());
                 value_instance.size
             }
             SourceType::Trait(_, _) => mem::ptr_width(),
@@ -67,11 +64,9 @@ impl SourceType {
             SourceType::Class(_, _) | SourceType::Lambda(_, _) | SourceType::Ptr => {
                 mem::ptr_width()
             }
-            SourceType::Value(value_id, params) => {
-                let value_instance_id = specialize_value_id_params(vm, *value_id, params.clone());
-                let value = vm.value_instances.idx(value_instance_id);
-
-                value.align
+            SourceType::Value(value_id, type_params) => {
+                let value_instance = value_instance(vm, *value_id, type_params.clone());
+                value_instance.align
             }
             SourceType::Trait(_, _) => mem::ptr_width(),
             SourceType::TypeParam(_) => panic!("no alignment for type variable."),