This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of Immediate status.

4445. sch_ must not be in moved-from state

Section: 33.13.5 [exec.task.scheduler] Status: Immediate Submitter: Tomasz Kamiński Opened: 2025-11-05 Last modified: 2025-11-05

Priority: Not Prioritized

View other active issues in [exec.task.scheduler].

View all other issues in [exec.task.scheduler].

View all issues with Immediate status.

Discussion:

Addresses US 239-367

As specified, there is an implicit precondition that sch_ is not moved from on all the member functions. If that is intended, the precondition should be made explicit.

[Kona 2025-11-05; approved by LWG. Status changed: New → Immediate.]

Proposed resolution:

This wording is relative to N5014.

  1. Modify 33.13.5 [exec.task.scheduler] as indicated:

    namespace std::execution {
  class task_scheduler {
    class ts-sender;                    // exposition only

    template<receiver R>
      class state;                      // exposition only

  public:
    using scheduler_concept = scheduler_t;

    template<class Sch, class Allocator = allocator<void>>
      requires (!same_as<task_scheduler, remove_cvref_t<Sch>>)
        && scheduler<Sch>
    explicit task_scheduler(Sch&& sch, Allocator alloc = {});

    task_scheduler(const task_scheduler&) = default;
    task_scheduler& operator=(const task_scheduler&) = default;

    ts-sender schedule();

    friend bool operator==(const task_scheduler& lhs, const task_scheduler& rhs)
        noexcept;
    template<class Sch>
      requires (!same_as<task_scheduler, Sch>)
      && scheduler<Sch>
    friend bool operator==(const task_scheduler& lhs, const Sch& rhs) noexcept;

  private:
    shared_ptr<void> sch_; // exposition only
  };
}