33 Execution control library [exec]

Subclause [exec.adapt] specifies a set of sender adaptors.

The bitwise inclusive or operator is overloaded for the purpose of creating sender chains.

The adaptors also support function call syntax with equivalent semantics.

Unless otherwise specified:

• (3.1)
  A sender adaptor is prohibited from causing observable effects, apart from moving and copying its arguments, before the returned sender is connected with a receiver using connect, and start is called on the resulting operation state.
• (3.2)
  A parent sender ([exec.async.ops]) with a single child sender sndr has an associated attribute object equal to FWD-ENV(get_env(sndr)) ([exec.fwd.env]).
• (3.3)
  A parent sender with more than one child sender has an associated attributes object equal to env<>{}.
• (3.4)
  When a parent sender is connected to a receiver rcvr, any receiver used to connect a child sender has an associated environment equal to FWD-ENV(get_env(rcvr)).
• (3.5)
  An adaptor whose child senders are all non-dependent ([exec.async.ops]) is itself non-dependent.
• (3.6)
  These requirements apply to any function that is selected by the implementation of the sender adaptor.
• (3.7)
  Recommended practice: Implementations should use the completion signatures of the adaptors to communicate type errors to users and to propagate any such type errors from child senders.

If a sender returned from a sender adaptor specified in [exec.adapt] is specified to include set_error_t(Err) among its set of completion signatures where decay_t<Err> denotes the type exception_ptr, but the implementation does not potentially evaluate an error completion operation with an exception_ptr argument, the implementation is allowed to omit the exception_ptr error completion signature from the set.