format関連をC++26でconstexpr対応 #1576

Author: faithandbrave

lang/cpp26.md

@@ -278,7 +278,7 @@ C++26とは、2026年中に改訂される予定の、C++バージョンの通
     - ポインタ出力のサポートを追加
     - 幅と精度を動的に指定した場合でも型の検証がコンパイル時に行われるよう仕様を見直し
     - コンパイル時の書式文字列だけでなく、実行時の書式文字列を渡せるよう仕様修正
-    - `constexpr`に対応
+    - 非ロケール版を`constexpr`に対応
 - [`std::to_string()`](/reference/string/to_string.md)と[`std::to_wstring()`](/reference/string/to_wstring.md)の整数オーバーロードが`constexpr`に対応
 - [`std::basic_string`](/reference/string/basic_string.md)クラスと[`std::basic_string_view`](/reference/string_view/basic_string_view.md)クラスに、部分文字列を[`std::basic_string_view`](/reference/string_view/basic_string_view.md)として取得するメンバ関数`subview()`を追加
 - [`std::basic_string`](/reference/string/basic_string.md)と[`std::basic_string_view`](/reference/string_view/basic_string_view.md)を[`std::basic_string`](/reference/string/basic_string.md)として連結させる`operator+`を追加

reference/format/basic_format_arg.md

@@ -56,7 +56,7 @@ namespace std {
 
 | 名前            | 説明                              | 対応バージョン |
 |-----------------|-----------------------------------|----------------|
-| `operator bool`   | `bool`への変換演算子(空の時`false`) | C++20          |
+| [`operator bool`](basic_format_arg/op_bool.md) | `bool`への変換演算子(空の時`false`) | C++20          |
 
 ## メンバ型
 

reference/format/basic_format_arg/op_bool.md

@@ -0,0 +1,33 @@
+# operator bool
+* format[meta header]
+* class[meta id-type]
+* std[meta namespace]
+* basic_format_arg[meta class]
+* cpp20[meta cpp]
+
+```cpp
+explicit operator bool() const noexcept;           // (1) C++20
+constexpr explicit operator bool() const noexcept; // (1) C++26
+```
+
+## 概要
+`bool`型への変換演算子。
+
+
+## 戻り値
+空でない場合に`true`を返す
+
+
+## バージョン
+### 言語
+- C++20
+
+### 処理系
+- [Clang](/implementation.md#clang): ??
+- [GCC](/implementation.md#gcc): ??
+- [ICC](/implementation.md#icc): ??
+- [Visual C++](/implementation.md#visual_cpp): ??
+
+## 参照
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)
+    - C++26から`constexpr`に対応した

reference/format/basic_format_arg/op_constructor.md

@@ -19,10 +19,16 @@ namespace std {
             const char_type*, basic_string_view<char_type>,
             const void*, handle> value;                                         // exposition only
 
-    template<class T> explicit basic_format_arg(T& v) noexcept;                 // (2) exposition only
+    template<class T>
+    explicit
+    basic_format_arg(T& v) noexcept;  // (2) C++20 exposition only
+    template<class T>
+    constexpr explicit
+    basic_format_arg(T& v) noexcept;  // (2) C++26 exposition only
 
   public:
-    basic_format_arg() noexcept; // (1)
+    basic_format_arg() noexcept;           // (1) C++20
+    constexpr basic_format_arg() noexcept; // (1) C++26
   };
 }
 ```
@@ -83,4 +89,6 @@ namespace std {
 
 ## 参照
 
-* [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)
+    - C++26から`constexpr`に対応した

reference/format/basic_format_args/get.md

@@ -7,7 +7,10 @@
 * cpp20[meta cpp]
 
 ```cpp
-basic_format_arg<Context> get(std::size_t i) const noexcept;
+basic_format_arg<Context>
+  get(std::size_t i) const noexcept; // (1) C++20
+constexpr basic_format_arg<Context>
+  get(std::size_t i) const noexcept; // (1) C++26
 ```
 * basic_format_arg[link /reference/format/basic_format_arg.md]
 
@@ -49,5 +52,6 @@ namespace std {
 - [Visual C++](/implementation.md#visual_cpp): ??
 
 ## 参照
-
-* [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)
+    - C++26から`constexpr`に対応した

reference/format/basic_format_args/op_constructor.md

@@ -7,10 +7,15 @@
 * cpp20[meta cpp]
 
 ```cpp
-basic_format_args() noexcept; // (1)
+basic_format_args() noexcept; // (1) C++20
 
 template<class... Args>
-basic_format_args(const format_arg_store<Context, Args...>& store) noexcept; // (2)
+basic_format_args(
+  const format_arg_store<Context, Args...>& store) noexcept; // (2) C++20
+template<class... Args>
+constexpr
+basic_format_args(
+  const format_arg_store<Context, Args...>& store) noexcept; // (2) C++26
 ```
 * basic_format_args[link /reference/format/basic_format_args.md]
 * format_arg_store[italic]
@@ -63,4 +68,6 @@ namespace std {
 
 ## 参照
 
-* [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)
+    - C++26から`constexpr`に対応した

reference/format/basic_format_context/advance_to.md

@@ -6,7 +6,8 @@
 * cpp20[meta cpp]
 
 ```cpp
-void advance_to(iterator it);
+void advance_to(iterator it);           // (1) C++20
+constexpr void advance_to(iterator it); // (1) C++26
 ```
 
 ## 概要
@@ -36,3 +37,5 @@ out_ = std::move(it);
 ## 参照
 
 - [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)
+    - C++26から`constexpr`に対応した

reference/format/basic_format_context/arg.md

@@ -6,7 +6,10 @@
 * cpp20[meta cpp]
 
 ```cpp
-basic_format_arg<basic_format_context> arg(size_t id) const;
+basic_format_arg<basic_format_context>
+  arg(size_t id) const;                // (1) C++20
+constexpr basic_format_arg<basic_format_context>
+  arg(size_t id) const;                // (1) C++26
 ```
 * basic_format_arg[link /reference/format/basic_format_arg.md]
 * basic_format_context[link /reference/format/basic_format_context.md]
@@ -28,3 +31,5 @@ basic_format_arg<basic_format_context> arg(size_t id) const;
 ## 参照
 
 - [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)
+    - C++26から`constexpr`に対応した

reference/format/basic_format_context/out.md

@@ -6,7 +6,8 @@
 * cpp20[meta cpp]
 
 ```cpp
-iterator out();
+iterator out();           // (1) C++20
+constexpr iterator out(); // (1) C++26
 ```
 
 ## 概要
@@ -36,3 +37,5 @@ return std::move(out_);
 ## 参照
 
 - [P0645R10 Text Formatting](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0645r10.html)
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)
+    - C++26から`constexpr`に対応した

reference/format/basic_format_string/op_constructor.md

@@ -7,8 +7,10 @@
 
 ```cpp
 template <class T>
-consteval basic_format_string(const T& s); // (1) C++23
+consteval
+basic_format_string(const T& s); // (1) C++23
 
+constexpr
 basic_format_string(runtime-format-string<charT> s) noexcept; // (2) C++26
 ```
 * runtime-format-string[link /reference/format/runtime-format-string.md]
@@ -97,3 +99,4 @@ namespace std {
 ## 参照
 - [P2216R3 `std::format` improvements](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2216r3.html)
 - [P2918R2 Runtime format strings II](https://open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2918r2.html)
+- [P3391R2 `constexpr std::format`](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3391r2.html)