tmp/tmp9xgww4mp/{from.md → to.md}
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| 1 |
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### Receiver concepts <a id="exec.recv.concepts">[[exec.recv.concepts]]</a>
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A receiver represents the continuation of an asynchronous operation. The
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`receiver` concept defines the requirements for a receiver type
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[[exec.async.ops]]. The `receiver_of` concept defines the requirements
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for a receiver type that is usable as the first argument of a set of
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completion operations corresponding to a set of completion signatures.
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The `get_env` customization point object is used to access a receiver’s
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associated environment.
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``` cpp
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namespace std::execution {
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template<class Rcvr>
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concept receiver =
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derived_from<typename remove_cvref_t<Rcvr>::receiver_concept, receiver_t> &&
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requires(const remove_cvref_t<Rcvr>& rcvr) {
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{ get_env(rcvr) } -> queryable;
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} &&
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move_constructible<remove_cvref_t<Rcvr>> && // rvalues are movable, and
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constructible_from<remove_cvref_t<Rcvr>, Rcvr>; // lvalues are copyable
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template<class Signature, class Rcvr>
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concept valid-completion-for = // exposition only
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requires (Signature* sig) {
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[]<class Tag, class... Args>(Tag(*)(Args...))
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requires callable<Tag, remove_cvref_t<Rcvr>, Args...>
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{}(sig);
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};
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template<class Rcvr, class Completions>
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concept has-completions = // exposition only
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requires (Completions* completions) {
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[]<valid-completion-for<Rcvr>...Sigs>(completion_signatures<Sigs...>*)
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{}(completions);
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};
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template<class Rcvr, class Completions>
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concept receiver_of =
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receiver<Rcvr> && has-completions<Rcvr, Completions>;
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}
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```
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Class types that are marked `final` do not model the `receiver` concept.
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Let `rcvr` be a receiver and let `op_state` be an operation state
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associated with an asynchronous operation created by connecting `rcvr`
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with a sender. Let `token` be a stop token equal to
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`get_stop_token(get_env(rcvr))`. `token` shall remain valid for the
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duration of the asynchronous operation’s lifetime [[exec.async.ops]].
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[*Note 1*: This means that, unless it knows about further guarantees
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provided by the type of `rcvr`, the implementation of `op_state` cannot
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use `token` after it executes a completion operation. This also implies
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that any stop callbacks registered on token must be destroyed before the
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invocation of the completion operation. — *end note*]
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