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4341. Missing rvalue reference qualification for task::connect()

Section: 33.13.6.2 [task.class] Status: Tentatively Ready Submitter: Dietmar Kühl Opened: 2025-08-31 Last modified: 2025-10-27

Priority: Not Prioritized

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Discussion:

Coroutines can't be copied. Thus, a task can be connect() just once. To represent that task::connect() should be rvalue reference qualified but currently it isn't.

[2025-10-17; Reflector poll.]

Set status to Tentatively Ready after five votes in favour during reflector poll.

"It's nice to rvalue qualify such a function, but it is not strictly necessary."

Proposed resolution:

In the synopsis in 33.13.6.2 [task.class] add rvalue reference qualification to task::connect():

namespace std::execution {
  template<class T, class Environment>
  class task {
    ...
    template<receiver Rcvr>
        state<Rcvr> connect(Rcvr&& rcvr) &&;
    ...
  }
}

In the specification in 33.13.6.3 [task.members] paragraph 3 add rvalue reference qualification to task::connect():

template<receiver Rcvr>
    state<Rcvr> connect(Rcvr&& rcvr) &&;

-3- Precondition: bool(handle) is true.

-4- Effects: Equivalent to:

    return state<Rcvr>(exchange(handle, {}), std::forward<Rcvr>(recv));