33 Execution control library [exec]

33.14 Execution scope utilities [exec.scope]

33.14.1 Execution scope concepts [exec.scope.concepts]

The scope_token concept defines the requirements on a type Token that can be used to create associations between senders and an async scope.

Let test-sender and test-env be unspecified types such that sender_in<test-sender, test-env> is modeled.

namespace std::execution { template<class Token> concept scope_token = copyable<Token> && requires(const Token token) { { token.try_associate() } -> same_as<bool>; { token.disassociate() } noexcept -> same_as<void>; { token.wrap(declval<test-sender>()) } -> sender_in<test-env>; }; }

A type Token models scope_token only if:

(3.1)
no exceptions are thrown from copy construction, move construction, copy assignment, or move assignment of objects of type Token; and
(3.2)
given an lvalue token of type (possibly const) Token, for all expressions sndr such that decltype((
sndr)) models sender:
- (3.2.1)
  token.wrap(sndr) is a valid expression,
- (3.2.2)
  decltype(token.wrap(sndr)) models sender, and
- (3.2.3)
  completion_signatures_of_t<decltype(token.wrap(sndr)), E> contains the same completion signatures as completion_signatures_of_t<decltype((sndr)), E> for all types E such that sender_in<decltype((sndr)), E> is modeled.