P2231R1: some functions will be constexpr in C++23

Author: wx257osn2

reference/variant/variant/emplace.md

@@ -7,18 +7,28 @@
 
 ```cpp
 template <class T, class... Args>
-T& emplace(Args&&... args);                              // (1)
+T& emplace(Args&&... args);                                        // (1) C++17
+template <class T, class... Args>
+constexpr T& emplace(Args&&... args);                              // (1) C++23
 
 template <class T, class U, class... Args>
-T& emplace(std::initializer_list<U> il, Args&&... args); // (2)
+T& emplace(std::initializer_list<U> il, Args&&... args);           // (2) C++17
+template <class T, class U, class... Args>
+constexpr T& emplace(std::initializer_list<U> il, Args&&... args); // (2) C++23
 
 template <std::size_t I, class... Args>
 variant_alternative_t<I, variant<Types...>>&
-  emplace(Args&&... args);                               // (3)
+  emplace(Args&&... args);                                         // (3) C++17
+template <std::size_t I, class... Args>
+constexpr variant_alternative_t<I, variant<Types...>>&
+  emplace(Args&&... args);                                         // (3) C++23
 
 template <std::size_t I, class U, class... Args>
 variant_alternative_t<I, variant<Types...>>&
-  emplace(std::initializer_list<U> il, Args&&... args);  // (4)
+  emplace(std::initializer_list<U> il, Args&&... args);            // (4) C++17
+template <std::size_t I, class U, class... Args>
+constexpr variant_alternative_t<I, variant<Types...>>&
+  emplace(std::initializer_list<U> il, Args&&... args);            // (4) C++23
 ```
 * variant_alternative_t[link /reference/variant/variant_alternative.md]
 
@@ -177,3 +187,6 @@ int main()
 - [Clang](/implementation.md#clang): 4.0.1
 - [GCC](/implementation.md#gcc): 7.3
 - [Visual C++](/implementation.md#visual_cpp): ??
+
+## 参照
+- [P2231R1 Missing `constexpr` in `std::optional` and `std::variant`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2231r1.html)

reference/variant/variant/op_assign.md

@@ -10,7 +10,9 @@ constexpr variant& operator=(const variant& rhs);              // (1)
 constexpr variant& operator=(variant&& t) noexcept(see below); // (2)
 
 template <class T>
-variant& operator=(T&& rhs) noexcept(see below);               // (3)
+variant& operator=(T&& rhs) noexcept(see below);               // (3) C++17
+template <class T>
+constexpr variant& operator=(T&& rhs) noexcept(see below);     // (3) C++23
 ```
 
 ## 概要
@@ -193,3 +195,4 @@ int main()
 ## 参照
 - [P0608R3 A sane variant converting constructor](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0608r3.html)
 - [P0602R4 `variant` and `optional` should propagate copy/move triviality](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0602r4.html)
+- [P2231R1 Missing `constexpr` in `std::optional` and `std::variant`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2231r1.html)

reference/variant/variant/op_destructor.md

@@ -6,7 +6,8 @@
 * cpp17[meta cpp]
 
 ```cpp
-~variant();
+~variant();            // C++17
+constexpr ~variant();  // C++23
 ```
 
 ## 概要
@@ -34,3 +35,6 @@
 
 ## 関連項目
 - [`std::is_trivially_destructible`](/reference/type_traits/is_trivially_destructible.md)
+
+## 参照
+- [P2231R1 Missing `constexpr` in `std::optional` and `std::variant`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2231r1.html)

reference/variant/variant/swap.md

@@ -6,7 +6,8 @@
 * cpp17[meta cpp]
 
 ```cpp
-void swap(variant& rhs) noexcept(see below);
+void swap(variant& rhs) noexcept(see below);            // C++17
+constexpr void swap(variant& rhs) noexcept(see below);  // C++23
 ```
 
 ## 概要
@@ -69,3 +70,6 @@ int main()
 - [Clang](/implementation.md#clang): 4.0.1
 - [GCC](/implementation.md#gcc): 7.3
 - [Visual C++](/implementation.md#visual_cpp): ??
+
+## 参照
+- [P2231R1 Missing `constexpr` in `std::optional` and `std::variant`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2231r1.html)

reference/variant/variant/swap_free.md

@@ -7,7 +7,9 @@
 ```cpp
 namespace std {
   template <class... Types>
-  void swap(variant<Types...>& x, variant<Types...>& y) noexcept(see below);
+  void swap(variant<Types...>& x, variant<Types...>& y) noexcept(see below);            // C++17
+  template <class... Types>
+  constexpr void swap(variant<Types...>& x, variant<Types...>& y) noexcept(see below);  // C++23
 }
 ```
 
@@ -71,3 +73,6 @@ int main()
 - [Clang](/implementation.md#clang): 4.0.1
 - [GCC](/implementation.md#gcc): 7.3
 - [Visual C++](/implementation.md#visual_cpp): ??
+
+## 参照
+- [P2231R1 Missing `constexpr` in `std::optional` and `std::variant`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2231r1.html)