[exec.snd.concepts] (original) (raw)

The sender concept defines the requirements for a sender type ([exec.async.ops]).

The sender_in concept defines the requirements for a sender type that can create asynchronous operations given an associated environment type.

The sender_to concept defines the requirements for a sender type that can connect with a specific receiver type.

The get_env customization point object is used to access a sender's associated attributes.

The connect customization point object is used to connect ([exec.async.ops]) a sender and a receiver to produce an operation state.

namespace std::execution { template<class Sigs> concept valid-completion-signatures = see below; template<class Sndr> concept is-sender = derived_from<typename Sndr::sender_concept, sender_t>;template<class Sndr> concept enable-sender = is-sender<Sndr> || is-awaitable<Sndr, _env-promise_<env<>>>; template<class Sndr> concept sender = bool(enable-sender<remove_cvref_t<Sndr>>) && requires (const remove_cvref_t<Sndr>& sndr) { { get_env(sndr) } -> queryable;} && move_constructible<remove_cvref_t<Sndr>> && constructible_from<remove_cvref_t<Sndr>, Sndr>;template<class Sndr, class Env = env<>> concept sender_in = sender<Sndr> && queryable<Env> && requires (Sndr&& sndr, Env&& env) { { get_completion_signatures(std::forward<Sndr>(sndr), std::forward<Env>(env)) } -> valid-completion-signatures;};template<class Sndr, class Rcvr> concept sender_to = sender_in<Sndr, env_of_t<Rcvr>> && receiver_of<Rcvr, completion_signatures_of_t<Sndr, env_of_t<Rcvr>>> && requires (Sndr&& sndr, Rcvr&& rcvr) { connect(std::forward<Sndr>(sndr), std::forward<Rcvr>(rcvr));};}

Given a subexpression sndr, let Sndr be decltype((sndr)) and let rcvr be a receiver with an associated environment whose type is Env.

A completion operation is a permissible completionfor Sndr and Envif its completion signature appears in the argument list of the specialization of completion_signatures denoted bycompletion_signatures_of_t<Sndr, Env>.

Sndr and Env model sender_in<Sndr, Env>if all the completion operations that are potentially evaluated by connecting sndr to rcvr and starting the resulting operation state are permissible completions for Sndr and Env.

A type models the exposition-only concept valid-completion-signaturesif it denotes a specialization of the completion_signatures class template.

The exposition-only conceptssender-of and sender-in-ofdefine the requirements for a sender type that completes with a given unique set of value result types.

namespace std::execution { template<class... As> using value-signature = set_value_t(As...); template<class Sndr, class Env, class... Values> concept sender-in-of = sender_in<Sndr, Env> && MATCHING-SIG( set_value_t(Values...), value_types_of_t<Sndr, Env, _value-signature_, type_identity_t>);template<class Sndr, class... Values> concept sender-of = sender-in-of<Sndr, env<>, Values...>;}

Let sndr be an expression such that decltype((sndr)) is Sndr.

The type tag_of_t<Sndr> is as follows:

• If the declarationauto&& [tag, data, ...children] = sndr;would be well-formed, tag_of_t<Sndr> is an alias for decltype(auto(tag)).
• Otherwise, tag_of_t<Sndr> is ill-formed.

Let sender-for be an exposition-only concept defined as follows:namespace std::execution { template<class Sndr, class Tag> concept sender-for = sender<Sndr> && same_as<tag_of_t<Sndr>, Tag>;}

For a type T,SET-VALUE-SIG(T) denotes the type set_value_t()if T is cv void; otherwise, it denotes the type set_value_t(T).