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execution: as_awaitable (#1384)
class-type,single-sender,forwarding-query
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‎reference/execution/class-type.md

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# class-type
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* execution[meta header]
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* concept[meta id-type]
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* std[meta namespace]
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* cpp26[meta cpp]
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```cpp
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namespace std {
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template<class T>
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concept class-type = decays-to<T, T> && is_class_v<T>; // exposition only
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}
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```
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* decays-to[link decays-to.md]
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* is_class_v[link /reference/type_traits/is_class.md]
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## 概要
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`class-type`は、型`T`がクラス型であることを表す説明専用のコンセプトである。
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## バージョン
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### 言語
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- C++26
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## 参照
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- [P2300R10 `std::execution`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html)

‎reference/execution/execution.md

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| 名前 | 説明 | 対応バージョン |
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|------|------|----------------|
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| [`execution::as_awaitable`](execution/as_awaitable.md.nolink) | Senderを[Awaitable型](/lang/cpp20/coroutines.md)へ変換 (customization point object) | C++26 |
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| [`execution::as_awaitable`](execution/as_awaitable.md) | Senderを[Awaitable型](/lang/cpp20/coroutines.md)へ変換 (customization point object) | C++26 |
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| [`execution::with_awaitable_senders`](execution/with_awaitable_senders.md) | [Promise型](/lang/cpp20/coroutines.md)の基底クラス (class template) | C++26 |
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‎reference/execution/execution/as_awaitable.md

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# as_awaitable
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* execution[meta header]
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* cpo[meta id-type]
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* std::execution[meta namespace]
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* cpp26[meta cpp]
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```cpp
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namespace std::execution {
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struct as_awaitable_t { unspecified };
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inline constexpr as_awaitable_t as_awaitable{};
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}
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```
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* unspecified[italic]
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## 概要
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`as_awaitable`は、オブジェクトを特定コルーチン内でAwaitableに変換するカスタマイゼーションポイントオブジェクトである。
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## 効果
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説明用の式`expr`と左辺値`p`に対して、型`Expr`を`decltype((expr))`、型`Promise`を[`decay_t`](/reference/type_traits/decay.md)`<decltype((p))>`とする。
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呼び出し式`as_awaitable(expr, p)`は、`expr`と`p`の評価が不定順で順序付けられることを除いて、下記と等価。
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- 適格であるならば、式`expr.as_awaitable(p)`
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- 適格要件 : 同式の型を`A`としたとき、[`is-awaitable`](../is-awaitable.md)`<A, Promise> == true`であるべき。
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- そうではなく、説明用の型`U`を`Promise`とは異なりかつ`await_transform`メンバ関数を持たない未規定の型としたとき、[`is-awaitable`](../is-awaitable.md)`<Expr, U> == true`ならば、式`(void(p), expr)`
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- 事前条件 : [`is-awaitable`](../is-awaitable.md)`<Expr, Promise> == true`、かつPromise型`U`のコルーチンにおける式`co_await expr`がPromise型`Promise`のコルーチンにおける同式と等しさを保持すること。
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- そうではなく、`awaitable-sender<Expr, Promise>`ならば、式`sender-awaitable{expr, p}`
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- そうでなければ、式`(void(p), expr)`
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## 説明専用エンティティ
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### コンセプト`awaitable-sender`
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```cpp
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namespace std::execution {
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template<class Sndr, class Promise>
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concept awaitable-sender =
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single-sender<Sndr, env_of_t<Promise>> &&
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sender_to<Sndr, awaitable-receiver> && // see below
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requires (Promise& p) {
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{ p.unhandled_stopped() } -> convertible_to<coroutine_handle<>>;
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};
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}
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```
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* single-sender[link single-sender.md]
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* sender_to[link sender_to.md]
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* convertible_to[link /reference/concepts/convertible_to.md]
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* coroutine_handle<>[link /reference/coroutine/coroutine_handle.md]
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* see below[italic]
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### クラステンプレート`sender-awaitable`
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```cpp
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namespace std::execution {
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template<class Sndr, class Promise>
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class sender-awaitable {
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struct unit {}; // exposition only
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using value-type = // exposition only
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single-sender-value-type<Sndr, env_of_t<Promise>>;
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using result-type = // exposition only
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conditional_t<is_void_v<value-type>, unit, value-type>;
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struct awaitable-receiver; // exposition only
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variant<monostate, result-type, exception_ptr> result{}; // exposition only
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connect_result_t<Sndr, awaitable-receiver> state; // exposition only
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public:
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sender-awaitable(Sndr&& sndr, Promise& p);
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static constexpr bool await_ready() noexcept { return false; }
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void await_suspend(coroutine_handle<Promise>) noexcept { start(state); }
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value-type await_resume();
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};
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}
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```
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* single-sender-value-type[link single-sender-value-type.md]
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* env_of_t[link env_of_t.md]
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* connect_result_t[link connect_result_t.md]
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* start[link start.md]
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* conditional_t[link /reference/type_traits/conditional.md]
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* is_void_v[link /reference/type_traits/is_void.md]
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* variant[link /reference/variant/variant.md]
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* monostate[link /reference/variant/monostate.md]
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* exception_ptr[link /reference/exception/exception_ptr.md]
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* coroutine_handle[link /reference/coroutine/coroutine_handle.md]
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### クラステンプレート`awaitable-receiver`
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説明専用のクラステンプレート`sender-awaitable<Sndr, Promise>::awaitable-receiver`は下記の通り定義される。
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```cpp
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struct awaitable-receiver {
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using receiver_concept = receiver_t;
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variant<monostate, result-type, exception_ptr>* result-ptr; // exposition only
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coroutine_handle<Promise> continuation; // exposition only
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// see below
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};
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```
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* receiver_t[link receiver.md]
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* variant[link /reference/variant/variant.md]
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* monostate[link /reference/variant/monostate.md]
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* exception_ptr[link /reference/exception/exception_ptr.md]
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* coroutine_handle[link /reference/coroutine/coroutine_handle.md]
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* see below[italic]
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説明用の式`rcvr`を`awaitable-reciever`型の右辺値、`crcvr`を`rcvr`をconst参照する左辺値、`vs`を式パック、`err`を`Err`型の式とする。このとき
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- [`constructible_from`](/reference/concepts/constructible_from.md)`<result-type, decltype((vs))...>`を満たすとき、式`set_value(rcvr, vs...)`は下記と等価。そうでなければ、式`set_value(rcvr, vs...)`は不適格となる。
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```cpp
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try {
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rcvr.result-ptr->template emplace<1>(vs...);
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} catch(...) {
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rcvr.result-ptr->template emplace<2>(current_exception());
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}
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rcvr.continuation.resume();
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```
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* template emplace[link /reference/variant/variant/emplace.md]
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* current_exception()[link /reference/exception/current_exception.md]
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* resume()[link /reference/coroutine/coroutine_handle/resume.md]
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- 式`set_error(rcvr, err)`は下記と等価。
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```cpp
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rcvr.result-ptr->template emplace<2>(AS-EXCEPT-PTR(err));
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rcvr.continuation.resume();
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```
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* template emplace[link /reference/variant/variant/emplace.md]
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* resume()[link /reference/coroutine/coroutine_handle/resume.md]
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- 式`set_stopped(rcvr)`は下記と等価。
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```cpp
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static_cast<coroutine_handle<>>(rcvr.continuation.promise().unhandled_stopped()).resume();
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```
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* coroutine_handle<>[link /reference/coroutine/coroutine_handle.md]
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* promise()[link /reference/coroutine/coroutine_handle/promise.md]
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* resume()[link /reference/coroutine/coroutine_handle/resume.md]
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- [`forwarding-query`](../forwarding-query.md)を満たす型の式`tag`とパック式`as`に対して、[`get_env`](get_env.md)`(crcvr).query(tag, as...)`は下記と等価。
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```cpp
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tag(get_env(as_const(crcvr.continuation.promise())), as...)
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```
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* get_env[link get_env.md]
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* as_const[link /reference/utility/as_const.md]
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* promise()[link /reference/coroutine/coroutine_handle/promise.md]
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```cpp
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sender-awaitable(Sndr&& sndr, Promise& p);
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```
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- 効果 : `state`を下記で初期化する。
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```cpp
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connect(std::forward<Sndr>(sndr),
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awaitable-receiver{addressof(result), coroutine_handle<Promise>::from_promise(p)})
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```
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* connect[link connect.md]
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* coroutine_handle[link /reference/coroutine/coroutine_handle.md]
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* from_promise[link /reference/coroutine/coroutine_handle/from_promise.md]
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```cpp
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value-type await_resume();
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```
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- 効果 : 下記と等価。
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```cpp
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if (result.index() == 2)
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rethrow_exception(get<2>(result));
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if constexpr (!is_void_v<value-type>)
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return std::forward<value-type>(get<1>(result));
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```
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* index()[link /reference/variant/variant/index.md]
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* get[link /reference/variant/variant/get.md]
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* rethrow_exception[link /reference/exception/rethrow_exception.md]
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* is_void_v[link /reference/type_traits/is_void.md]
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## カスタマイゼーションポイント
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`expr`に対して、適格であるならば式`expr.as_awaitable(p)`が呼び出される。
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## バージョン
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### 言語
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- C++26
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### 処理系
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- [Clang](/implementation.md#clang): ??
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- [GCC](/implementation.md#gcc): ??
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- [ICC](/implementation.md#icc): ??
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- [Visual C++](/implementation.md#visual_cpp): ??
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## 関連項目
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- [`execution::with_awaitable_senders`](with_awaitable_senders.md)
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- [C++20 コルーチン](/lang/cpp20/coroutines.md)
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## 参照
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- [P2300R10 `std::execution`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html)

‎reference/execution/execution/sender_adaptor_closure.md

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struct sender_adaptor_closure { };
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}
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```
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* class-type[link class-type.md.nolink]
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* class-type[link ../class-type.md]
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## 概要
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`sender_adaptor_closure`は、ユーザ定義のパイプ可能Senderアダプタクロージャオブジェクトの実装を補助するクラステンプレートである。

‎reference/execution/execution/single-sender-value-type.md

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## 関連項目
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- [`execution::stopped_as_optional`](stopped_as_optional.md)
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- [`sender-awaitable`](sender-awaitable.md.nolink)
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- [`execution::as_awaitable`](as_awaitable.md)
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## 参照

‎reference/execution/execution/single-sender.md

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# single-sender
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* execution[meta header]
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* type-alias[meta id-type]
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* std::execution[meta namespace]
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* cpp26[meta cpp]
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```cpp
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template<class Sndr, class Env>
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concept single-sender = sender_in<Sndr, Env> &&
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requires {
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typename single-sender-value-type<Sndr, Env>;
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};
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```
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* sender_in[link sender_in.md]
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* single-sender-value-type[link single-sender-value-type.md]
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## 概要
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`single-sender`は、実行制御ライブラリの仕様定義で用いられる説明専用のエイリアステンプレートである。
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## バージョン
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### 言語
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- C++26
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## 関連項目
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- [`execution::as_awaitable`](as_awaitable.md)
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## 参照
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- [P2300R10 `std::execution`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html)

‎reference/execution/execution/with_awaitable_senders.md

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};
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}
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```
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* class-type[link class-type.md.nolink]
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* class-type[link ../class-type.md]
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* terminate()[link /reference/exception/terminate.md]
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* coroutine_handle[link /reference/coroutine/coroutine_handle.md]
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* address()[link /reference/coroutine/coroutine_handle/address.md]
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## 関連項目
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- [`execution::as_awaitable`](as_awaitable.md.nolink)
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- [`execution::as_awaitable`](as_awaitable.md)
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- [コルーチン](/lang/cpp20/coroutines.md)
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‎reference/execution/execution/with_awaitable_senders/await_transform.md

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await_transform(Value&& value);
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```
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* call-result-t[link /reference/functional/call-result-t.md]
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* as_awaitable_t[link ../as_awaitable.md.nolink]
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* as_awaitable_t[link ../as_awaitable.md]
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## 概要
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コルーチンの[`co_await`演算子](/lang/cpp20/coroutines.md)にアダプトし、[`as_awaitable`](../as_awaitable.md.nolink)で変換したAwaitableオブジェクトを返す。
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コルーチンの[`co_await`演算子](/lang/cpp20/coroutines.md)にアダプトし、[`as_awaitable`](../as_awaitable.md)で変換したAwaitableオブジェクトを返す。
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## 効果
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```cpp
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return as_awaitable(std::forward<Value>(value), static_cast<Promise&>(*this));
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```
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* as_awaitable[link ../as_awaitable.md.nolink]
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* as_awaitable[link ../as_awaitable.md]
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## バージョン
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## 関連項目
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- [`execution::as_awaitable`](../as_awaitable.md.nolink)
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- [`execution::as_awaitable`](../as_awaitable.md)
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## 参照

‎reference/execution/forwarding-query.md

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# forwarding-query
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* execution[meta header]
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* concept[meta id-type]
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* std[meta namespace]
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* cpp26[meta cpp]
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```cpp
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namespace std {
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template<class T>
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concept forwarding-query = forwarding_query(T{}); // exposition only
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}
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```
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* forwarding_query[link forwarding_query.md]
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## 概要
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`forwarding_query`は、型`T`が[クエリ可能アダプタを通じて転送可能](forwarding_query.md)か否かを確認する説明専用のコンセプトである。
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## バージョン
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### 言語
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- C++26
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## 関連項目
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- [`forwarding_query`](forwarding_query.md)
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## 参照
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- [P2300R10 `std::execution`](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2300r10.html)

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