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4448. Do not forward fn in completion_signatures

Section: 33.10 [exec.cmplsig] Status: Immediate Submitter: Tomasz Kamiński Opened: 2025-11-05 Last modified: 2025-11-05

Priority: Not Prioritized

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Discussion:

fn can be called multiple times and therefore should not be forwarded.

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

Proposed resolution:

This wording is relative to N5014.

1. Modify 33.10 [exec.cmplsig] as indicated:

   -8-

   namespace std::execution {
     template<completion-signature... Fns>
       struct completion_signatures {
         template<class Tag>
           static constexpr size_t count-of(Tag) { return see below; }
   
         template<class Fn>
           static constexpr void for-each(Fn&& fn) {               // exposition only
             (std::forward<Fn>(fn)fn(static_cast<Fns*>(nullptr)), ...);
           }
       };
   
     […]
   }