execution: C++26 P3284R4 (#1501)

yohhoy · yohhoy · commit 403ba99ec22c · 2025-08-21T20:27:10.000+09:00
- write_envアダプタ (write-envから昇格)
- unstoppableアダプタ
diff --git a/reference/execution/execution.md b/reference/execution/execution.md
@@ -110,6 +110,8 @@ namespace std::execution {
 | 名前 | 説明 | 対応バージョン |
 |------|------|----------------|
 | [`execution::sender_adaptor_closure`](execution/sender_adaptor_closure.md) | パイプライン記法をサポートするSenderアダプタ実装補助 (class template) | C++26 |
+| [`execution::write_env`](execution/write_env.md) | Receiver環境を書き換える (customization point object) | C++26 |
+| [`execution::unstoppable`](execution/unstoppable.md) | 停止要求を遮断する (customization point object) | C++26 |
 | [`execution::starts_on`](execution/starts_on.md) | 指定Scheduler上で開始する (customization point object) | C++26 |
 | [`execution::continues_on`](execution/continues_on.md) | 指定Scheduler上で継続する (customization point object) | C++26 |
 | [`execution::on`](execution/on.md) | 指定Senderのみ別Scheduler上で実行する (customization point object) | C++26 |
@@ -162,5 +164,6 @@ Senderコンシューマは名前空間 `std::this_thread` で定義される。
 ## 参照
 - [P0024R2 The Parallelism TS Should be Standardized](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0024r2.html)
 - [P2300R10 `std::execution`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html)
+- [P3284R4 `write_env` and `unstoppable` Sender Adaptors](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3284r4.html)
 - [P3557R3 High-Quality Sender Diagnostics with Constexpr Exceptions](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3557r3.html)
 - [P3682R0 Remove `std::execution::split`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3682r0.pdf)
diff --git a/reference/execution/execution/child-type.md b/reference/execution/execution/child-type.md
@@ -21,11 +21,11 @@ namespace std::execution {
 - C++26
 
 ## 関連項目
+- [`execution::write_env`](write_env.md)
 - [`execution::schedule_from`](schedule_from.md)
 - [`execution::let_value`](let_value.md)
 - [`execution::into_variant`](into_variant.md)
 - [`execution::stopped_as_optional`](stopped_as_optional.md)
-- [`write-env`](write-env.md)
 
 
 ## 参照
diff --git a/reference/execution/execution/data-type.md b/reference/execution/execution/data-type.md
@@ -22,11 +22,11 @@ namespace std::execution {
 
 ## 関連項目
 - [`execution::read_env`](read_env.md)
+- [`execution::write_env`](write_env.md)
 - [`execution::schedule_from`](schedule_from.md)
 - [`execution::then`](then.md)
 - [`execution::let_value`](let_value.md)
 - [`execution::bulk`](bulk.md)
-- [`write-env`](write-env.md)
 
 
 ## 参照
diff --git a/reference/execution/execution/on.md b/reference/execution/execution/on.md
@@ -108,11 +108,11 @@ transform_sender(
       if constexpr (same_as<decltype(orig_sch), not-a-scheduler>) {
         return not-a-sender{};
       } else {
-        return write-env(
+        return write_env(
           continues_on(
             std::forward_like<OutSndr>(closure)(
               continues_on(
-                write-env(std::forward_like<OutSndr>(child), SCHED-ENV(orig_sch)),
+                write_env(std::forward_like<OutSndr>(child), SCHED-ENV(orig_sch)),
                 sch)),
             orig_sch),
           SCHED-ENV(sch));
@@ -128,7 +128,7 @@ transform_sender(
     * get_env[link get_env.md]
     * query-with-default[link query-with-default.md]
     * not-a-sender[link not-a-sender.md]
-    * write-env[link write-env.md]
+    * write_env[link write_env.md]
     * SCHED-ENV[link scheduler.md]
     * std::move[link /reference/utility/move.md]
 
diff --git a/reference/execution/execution/unstoppable.md b/reference/execution/execution/unstoppable.md
@@ -0,0 +1,39 @@
+# unstoppable
+* execution[meta header]
+* cpo[meta id-type]
+* std::execution[meta namespace]
+* cpp26[meta cpp]
+
+```cpp
+namespace std::execution {
+  inline constexpr unspecified unstoppable{};
+}
+```
+* unspecified[italic]
+
+## 概要
+`unstoppable`は、[`get_stop_token`](../get_stop_token.md)クエリオブジェクトが[`never_stop_token`](/reference/stop_token/never_stop_token.md)を返すよう書き換えて、内側[Sender](sender.md)と外側[Receiver](receiver.md)の[環境](../queryable.md)を接続するSenderアダプタである。
+
+
+## 効果
+説明用の式`sndr`に対して、呼び出し式`unstoppable(sndr)`は式[`write_env`](write_env.md)`(sndr,` [`prop`](prop.md)`(`[`get_stop_token`](../get_stop_token.md)`,` [`never_stop_token{}`](/reference/stop_token/never_stop_token.md)`))`と等価。
+
+
+## バージョン
+### 言語
+- C++26
+
+### 処理系
+- [Clang](/implementation.md#clang): ??
+- [GCC](/implementation.md#gcc): ??
+- [ICC](/implementation.md#icc): ??
+- [Visual C++](/implementation.md#visual_cpp): ??
+
+
+## 関連項目
+- [`execution::write_env`](write_env.md)
+
+
+## 参照
+- [P2300R10 `std::execution`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html)
+- [P3284R4 `write_env` and `unstoppable` Sender Adaptors](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3284r4.html)
diff --git a/reference/execution/execution/write_env.md b/reference/execution/execution/write_env.md
@@ -1,30 +1,29 @@
-# write-env
+# write_env
 * execution[meta header]
-* function template[meta id-type]
+* cpo[meta id-type]
 * std::execution[meta namespace]
 * cpp26[meta cpp]
 
 ```cpp
-template<sender Sndr, queryable Env>
-constexpr auto write-env(Sndr&& sndr, Env&& env);  // exposition only
+namespace std::execution {
+  inline constexpr unspecified write_env{};
+}
 ```
+* unspecified[italic]
 
 ## 概要
-`write-env`は、Senderアルゴリズム動作仕様定義で用いられる説明専用のSenderアダプタである。
+`write_env`は、入力[Sender](sender.md)と[クエリ可能オブジェクト](../queryable.md)を受け取り、[Receiver](receiver.md)`rcvr`と[接続(connect)](connect.md)される際に、クエリ可能オブジェクトと[`get_env`](get_env.md)`(rcvr)`を合成した環境に関連付けられたReceiverと接続されるSenderを生成するSenderアダプタである。
 
-[クエリ可能オブジェクト](../queryable.md)`env`と接続先[Receiver](receiver.md)の環境を合成した、新たなクエリ可能オブジェクトに関連付けれられたSenderを生成する。
 
+## 効果
+説明用の式`sndr`と`env`に対して、`decltype((sndr))`が[`sender`](sender.md)を満たさない、もしくは`decltype((env))`が[`queryable`](../queryable.md)を満たさないとき、呼び出し式`write_env(sndr, env)`は不適格となる。
 
-## 戻り値
-説明専用の`write-env-t`を空のクラスとしたとき、下記を返す。
-
-```cpp
-make-sender(write-env-t(), std::forward<Env>(env), std::forward<Sndr>(sndr))
-```
-* make-sender[link make-sender.md]
+そうでなければ、呼び出し式`write_env(sndr, env)`は式[`make-sender`](make-sender.md)`(write_env, env, sndr)`と等価。
 
 
 ### Senderアルゴリズムタグ
+説明用の`write-env-t`を`decltype(auto(write_env))`とする。
+
 Senderアルゴリズム動作説明用のクラステンプレート[`impls-for`](impls-for.md)に対して、下記の特殊化が定義される。
 
 ```cpp
@@ -59,12 +58,20 @@ struct impls-for<write-env-t> : default-impls {
 ### 言語
 - C++26
 
+### 処理系
+- [Clang](/implementation.md#clang): ??
+- [GCC](/implementation.md#gcc): ??
+- [ICC](/implementation.md#icc): ??
+- [Visual C++](/implementation.md#visual_cpp): ??
+
 
 ## 関連項目
 - [`execution::on`](on.md)
+- [`execution::unstoppable`](unstoppable.md)
 
 
 ## 参照
 - [P2300R10 `std::execution`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html)
 - [P3396R1 std::execution wording fixes](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p3396r1.html)
 - [P3557R3 High-Quality Sender Diagnostics with Constexpr Exceptions](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3557r3.html)
+- [P3284R4 `write_env` and `unstoppable` Sender Adaptors](https://open-std.org/jtc1/sc22/wg21/docs/papers/2025/p3284r4.html)
