34 Execution control library [exec]

34.7 Receivers [exec.recv]

34.7.1 Receiver concepts [exec.recv.concepts]

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

34.7.2 execution​::​set_value [exec.set.value]

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set_value is a value completion function ([exec.async.ops]).
Its associated completion tag is set_value_t.
The expression set_value(rcvr, vs...) for a subexpression rcvr and pack of subexpressions vs is ill-formed if rcvr is an lvalue or an rvalue of const type.
Otherwise, it is expression-equivalent to MANDATE-NOTHROW(rcvr.set_value(vs...)).

34.7.3 execution​::​set_error [exec.set.error]

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set_error is an error completion function ([exec.async.ops]).
Its associated completion tag is set_error_t.
The expression set_error(rcvr, err) for some subexpressions rcvr and err is ill-formed if rcvr is an lvalue or an rvalue of const type.
Otherwise, it is expression-equivalent to MANDATE-NOTHROW(rcvr.set_error(err)).

34.7.4 execution​::​set_stopped [exec.set.stopped]

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set_stopped is a stopped completion function ([exec.async.ops]).
Its associated completion tag is set_stopped_t.
The expression set_stopped(rcvr) for a subexpression rcvr is ill-formed if rcvr is an lvalue or an rvalue of const type.
Otherwise, it is expression-equivalent to MANDATE-NOTHROW(rcvr.set_stopped()).