34 Execution control library [exec]

34.12 Coroutine utilities [exec.coro.util]

34.12.2 execution​::​with_awaitable_senders [exec.with.awaitable.senders]

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with_awaitable_senders, when used as the base class of a coroutine promise type, makes senders awaitable in that coroutine type.
In addition, it provides a default implementation of unhandled_stopped such that if a sender completes by calling set_stopped, it is treated as if an uncatchable "stopped" exception were thrown from the await-expression.
[Note 1: 
The coroutine is never resumed, and the unhandled_stopped of the coroutine caller's promise type is called.
— end note]
namespace std::execution { template<class-type Promise> struct with_awaitable_senders { template<class OtherPromise> requires (!same_as<OtherPromise, void>) void set_continuation(coroutine_handle<OtherPromise> h) noexcept; coroutine_handle<> continuation() const noexcept { return continuation; } coroutine_handle<> unhandled_stopped() noexcept { return stopped-handler(continuation.address()); } template<class Value> see below await_transform(Value&& value); private: [[noreturn]] static coroutine_handle<> default-unhandled-stopped(void*) noexcept { // exposition only terminate(); } coroutine_handle<> continuation{}; // exposition only coroutine_handle<> (*stopped-handler)(void*) noexcept = // exposition only &default-unhandled-stopped; }; }
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template<class OtherPromise> requires (!same_as<OtherPromise, void>) void set_continuation(coroutine_handle<OtherPromise> h) noexcept;
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Effects: Equivalent to: continuation = h; if constexpr ( requires(OtherPromise& other) { other.unhandled_stopped(); } ) { stopped-handler = [](void* p) noexcept -> coroutine_handle<> { return coroutine_handle<OtherPromise>::from_address(p) .promise().unhandled_stopped(); }; } else { stopped-handler = &default-unhandled-stopped; }
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template<class Value> call-result-t<as_awaitable_t, Value, Promise&> await_transform(Value&& value);
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Effects: Equivalent to: return as_awaitable(std::forward<Value>(value), static_cast<Promise&>(*this));