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Variant match expression and object #44

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Mar 14, 2023
Merged

Variant match expression and object #44

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162 changes: 80 additions & 82 deletions include/utils/match.hxx
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@
///
/// License: MIT
///
/// Copyright: Copyright (c) 2022
/// Copyright: Copyright (c) 2022-23
/// \file match.hxx

#ifndef CORTEX_MATCH
Expand All @@ -26,111 +26,109 @@
# include <concepts>
#endif /// __cpp_concepts >= 201907L

namespace cxl
namespace cxl::utils
{
namespace utils

/// \brief match structure
///
/// \details Inherits the properties
/// of the variadic template of
/// invocables and interfaces the
/// invocables `()` operators.
///
/// \tparam ...Fs
template<typename... Fs>
struct match : Fs...
{
/// \brief match structure
///
/// \details Inherits the properties
/// of the variadic template of
/// invocables and interfaces the
/// invocables `()` operators.
///
/// \tparam ...Fs concept: std::invocable
template<typename... Fs>
struct match : Fs...
{

/// \brief Forward Constructor
///
/// \details Consumes all function types
/// and forwards them to the variadic constructor
/// of the invocables.
///
/// \tparam ...Ts
///
/// \param ...ts
template<class... Ts>
explicit match(Ts&&... ts)
: Fs { std::forward<Ts>(ts) }... { }

/// \brief Invocation declaration
///
/// \details Declares `match` to be using
/// the invocation operators `()`.
using Fs::operator()...;
};

/// \brief Template Deduction Guide
template<typename... Fs>
match(Fs&&...) -> match<std::remove_reference_t<Fs>...>;

/// \brief Match Expression Notation

/// \brief Forward Constructor
///
/// \details Overloads `>>` to reverse the argument
/// order of a match expression for a cleaner syntax
/// with existing match types.
/// \details Consumes all function types
/// and forwards them to the variadic constructor
/// of the invocables.
///
/// \tparam ...Ts
/// \tparam ...Fs concept: std::invocable
/// \param var type: std::variant<Ts...>
/// \param m type match<Fs...>&&
/// \return decltype(auto)
template<typename... Ts, typename... Fs>
constexpr auto
operator| (const std::variant<Ts...>& var,
const match<Fs...>& m) -> void {
std::visit(m, var);
}

/// \brief Match Expression Assignment Overload
///
/// \details Overloads the `>>=` operator to
/// reverse the argument order of a match
/// expression for a cleaner syntax with existing
/// match types and to denote an explicit syntax
/// for match expressions that return a value.
/// \param ...ts
template<class... Ts>
explicit match(Ts&&... ts)
: Fs { std::forward<Ts>(ts) }... { }

/// \brief Invocation declaration
///
/// \tparam R
/// \tparam ...Ts
/// \tparam ...Fs concept: std::invocable
/// \param var type: const std::variant<Ts...>&
/// \param m type: match<Fs...>&&
/// \return R
template<typename... Ts, typename... Fs>
constexpr auto
operator|= (const std::variant<Ts...>& var,
const match<Fs...>& m) -> decltype(auto) {
return std::visit(m, var);
}
/// \details Declares `match` to be using
/// the invocation operators `()`.
using Fs::operator()...;
};

/// \brief Template Deduction Guide
template<typename... Fs>
match(Fs&&...) -> match<std::remove_reference_t<Fs>...>;

} // namespace utils
/// \brief Match Expression Notation
///
/// \details Overloads `>>` to reverse the argument
/// order of a match expression for a cleaner syntax
/// with existing match types.
///
/// \tparam ...Ts
/// \tparam ...Fs
/// \param var type: const std::variant<Ts...>&
/// \param m type const match<Fs...>&
/// \return auto
template<typename... Ts, typename... Fs>
constexpr auto
operator>> (
const std::variant<Ts...>& var,
const match<Fs...>& m
) -> void
{ std::visit(m, var); }

/// \brief Match Expression Assignment Overload
///
/// \details Overloads the `>>=` operator to
/// reverse the argument order of a match
/// expression for a cleaner syntax with existing
/// match types and to denote an explicit syntax
/// for match expressions that return a value.
///
/// \tparam ...Ts
/// \tparam ...Fs
/// \param var type: const std::variant<Ts...>&
/// \param m type: const match<Fs...>&
/// \return decltype(auto)
template<typename... Ts, typename... Fs>
constexpr auto
operator<< (
const std::variant<Ts...>& var,
const match<Fs...>& m
) -> decltype(auto)
{ return std::visit(m, var); }

/// \brief Wildcard Empty Placeholder
///
/// \details Names a placeholder type
/// that can match to anything in a match
/// expression. The value is un-retrievable
/// from `_`, use `auto&& <name>` to have a
/// from `bottom`, use `auto&& <var-name>` to have a
/// retrievable value.
struct _
struct match_any
{
template<typename T>
explicit constexpr _([[maybe_unused]] T&& t) noexcept { }
explicit constexpr match_any([[maybe_unused]] T&& t) noexcept { }

explicit constexpr _(const _&) noexcept = delete;
explicit constexpr _(_&&) noexcept = delete;
explicit constexpr match_any(const match_any&) noexcept = delete;
explicit constexpr match_any(match_any&&) noexcept = delete;

constexpr auto
operator= (const _&) noexcept -> _& = delete;
operator= (const match_any&) noexcept -> match_any& = delete;

constexpr auto
operator= (_&&) noexcept -> _& = delete;
operator= (match_any&&) noexcept -> match_any& = delete;

constexpr ~_() noexcept = delete;
constexpr ~match_any() noexcept = delete;
};

} // namespace cxl
} // namespace cxl::utils

#endif /// CORTEX_MATCH
68 changes: 37 additions & 31 deletions src/utils/match.test.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -8,43 +8,48 @@
#include <utils/match.hxx>
#include <variant>

TEST_CASE("match test") {
TEST_CASE("match test")
{
using namespace std::literals;
using var_t = std::variant<int, float, std::string>;

auto var7 { var_t { 7 } };
auto varstr { var_t { "Hello"s } };
auto varf { var_t { 6.78f } };

SECTION("match with std::visit") {
std::visit(cxl::utils::match {
[](std::string& s) {
fmt::print("s: std::string = {}\n", s);
},
[](int& i) { fmt::print("i: int = {}\n", i); },
[](float& f) { fmt::print("s: float = {}\n", f); },
[](cxl::_) { fmt::print("Other\n"); } },
var7);
SECTION("match with std::visit")
{
std::visit(
cxl::utils::match {
[](std::string& s) { fmt::print("s: std::string = {}\n", s); },
[](int& i) { fmt::print("i: int = {}\n", i); },
[](float& f) { fmt::print("s: float = {}\n", f); },
[](cxl::utils::match_any) { fmt::print("Other\n"); }
},
var7
);

auto r = std::visit(
cxl::utils::match {
[]([[maybe_unused]] std::string& s) { return "String"s; },
[]([[maybe_unused]] int& i) { return "Int"s; },
[]([[maybe_unused]] float& f) { return "Float"s; },
[](cxl::_) { return "Other"s; } },
varf);
[](cxl::utils::match_any) { return "Other"s; } },
varf
);

REQUIRE(r == "Float"s);

fmt::print("r = {}\n", r);
}

SECTION("match expression syntax sugar") {
SECTION("match expression syntax sugar")
{
auto print_match = cxl::utils::match {
[](std::string s) { fmt::print("s: std::string = {}\n", s); },
[](int i) { fmt::print("i: int = {}\n", i); },
[](float f) { fmt::print("s: float = {}\n", f); },
[](cxl::_) { fmt::print("Other\n"); }
[](cxl::utils::match_any) { fmt::print("Other\n"); }
};

using namespace cxl;
Expand All @@ -53,37 +58,38 @@ TEST_CASE("match test") {
[]([[maybe_unused]] std::string s) { return "String"s; },
[]([[maybe_unused]] int i) { return "Int"s; },
[]([[maybe_unused]] float f) { return "Float"s; },
[](_) { return "Other"s; }
[](utils::match_any) { return "Other"s; }
};

SECTION("Regular match expression") {
varstr |
cxl::utils::match {
[](std::string s) {
fmt::print("s: std::string = {}\n", s);
},
[](int i) { fmt::print("i: int = {}\n", i); },
[](float f) { fmt::print("s: float = {}\n", f); },
[](cxl::_) { fmt::print("Other\n"); }
};
SECTION("Regular match expression")
{
varstr >> cxl::utils::match {
[](std::string s) { fmt::print("s: std::string = {}\n", s); },
[](int i) { fmt::print("i: int = {}\n", i); },
[](float f) { fmt::print("s: float = {}\n", f); },
[](cxl::utils::match_any) { fmt::print("Other\n"); }
};

varf | print_match;
varf >> print_match;

REQUIRE(std::is_void_v<decltype(var7 | name_match)> == true);
REQUIRE(std::is_void_v<decltype(var7 >> name_match)> == true);
}

SECTION("Returning match expression") {
auto r = varstr |= cxl::utils::match {
SECTION("Returning match expression")
{
auto r = varstr << cxl::utils::match {
[]([[maybe_unused]] std::string s) { return "String"s; },
[]([[maybe_unused]] int i) { return "Int"s; },
[]([[maybe_unused]] float f) { return "Float"s; },
[](cxl::_) { return "Other"s; }
[](cxl::utils::match_any) { return "Other"s; }
};

fmt::print("r = {}\n", r);
REQUIRE(r == "String");

auto name = var7 |= name_match;
auto name = var7 << name_match;
fmt::print("name = {}\n", name);
REQUIRE(name == "Int");
}
}
}