[exec.factories]

The name schedule denotes a customization point object.

For a subexpression sch, the expression schedule(sch) is expression-equivalent to sch.schedule().

If the expression get_completion_scheduler<set_value_t>(get_env(sch.schedule() == sch is ill-formed or evaluates to false, the behavior of calling schedule(sch) is undefined.

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 of just, 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

(2.1)
(movable-value<Ts> &&.) is false, or
(2.2)
just-cpo is just_error and sizeof.(ts) == 1 is false, or
(2.3)
just-cpo is just_stopped and sizeof.(ts) == 0 is false.

Otherwise, it is expression-equivalent to make-sender(just-cpo, product-type{ts..}).

For just, just_error, and just_stopped, let set-cpo be set_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).); }; }; }

33.9.11.3 execution::read_env [exec.read.env]

read_env is a sender factory for a sender whose asynchronous operation completes synchronously in its start operation with a value completion result equal to a value read from the receiver's associated environment.

read_env is a customization point object.

For some query object q, the expression read_env(q) is expression-equivalent to make-sender(read_env, q).

The exposition-only class template impls-for ([exec.snd.expos]) is specialized for read_env as follows:

🔗

namespace std::execution { template<> struct impls-for<decayed-typeof<read_env>> : default-impls { static constexpr auto start = [](auto query, auto& rcvr) noexcept -> void { TRY-SET-VALUE(rcvr, query(get_env(rcvr)); }; }; template<class Sndr, class Env> static consteval void check-types(); }

🔗

template<class Sndr, class Env>
  static consteval void check-types();

Throws: An exception of type unspecified-exception ([exec.snd.general]) if the expression Q()(env) is ill-formed or has type void, where env is an lvalue subexpression whose type is Env.

33.9.11.2 execution​::​just, execution​::​just_error, execution​::​just_stopped [exec.just]

33.9.11.3 execution​::​read_env [exec.read.env]

33.9.11.2 execution::just, execution::just_error, execution::just_stopped [exec.just]

33.9.11.3 execution::read_env [exec.read.env]