34 Execution control library [exec]

34.7 Receivers [exec.recv]

34.7.1 Receiver concepts [exec.recv.concepts]

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>; }

Class types that are marked final do not model the receiver concept.

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]