2.0 KiB
[exec.just]
33 Execution control library [exec]
33.9 Senders [exec.snd]
33.9.11 Sender factories [exec.factories]
33.9.11.2 execution::just, execution::just_error, execution::just_stopped [exec.just]
just, just_error, and just_stopped are sender factories whose asynchronous operations complete synchronously in their start operation with a value completion operation, an error completion operation, or a stopped completion operation, respectively.
The names just, just_error, and just_stopped denote customization point objects.
Let just-cpo be one ofjust, just_error, or just_stopped.
For a pack of subexpressions ts, let Ts be the pack of types decltype((ts)).
The expression just-cpo(ts...) is ill-formed if
(movable-value &&...) is false, or
just-cpo is just_error andsizeof...(ts) == 1 is false, or
just-cpo is just_stopped andsizeof...(ts) == 0 is false.
Otherwise, it is expression-equivalent tomake-sender(just-cpo, product-type{ts...}).
For just, just_error, and just_stopped, let set-cpo beset_value, set_error, and set_stopped, respectively.
The exposition-only class template impls-for ([exec.snd.expos]) is specialized for just-cpo as follows:namespace std::execution {template<>struct impls-for<decayed-typeof<just-cpo>> : default-impls {static constexpr auto start =[](auto& state, auto& rcvr) noexcept -> void {auto& [...ts] = state; set-cpo(std::move(rcvr), std::move(ts)...); }; };}