34 Execution control library [exec]

For the purposes of this subclause, a sender is an object whose type satisfies the sender concept ([exec.async.ops]).

Subclauses [exec.factories] and [exec.adapt] define customizable algorithms that return senders Each algorithm has a default implementation.

Let sndr be the result of an invocation of such an algorithm or an object equal to the result ([concepts.equality]), and let Sndr be decltype((sndr)).

Let rcvr be a receiver of type Rcvr with associated environment env of type Env such that sender_to<Sndr, Rcvr> is true.

For the default implementation of the algorithm that produced sndr, connecting sndr to rcvr and starting the resulting operation state ([exec.async.ops]) necessarily results in the potential evaluation ([basic.def.odr]) of a set of completion operations whose first argument is a subexpression equal to rcvr.

Let Sigs be a pack of completion signatures corresponding to this set of completion operations.

Then the type of the expression get_completion_signatures(sndr, env) is a specialization of the class template completion_signatures ([exec.util.cmplsig]), the set of whose template arguments is Sigs.

If a user-provided implementation of the algorithm that produced sndr is selected instead of the default, any completion signature that is in the set of types denoted by completion_signatures_of_t<Sndr, Env> and that is not part of Sigs shall correspond to error or stopped completion operations, unless otherwise specified.