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3303. Bad "constexpr" marker for destroy/destroy_n

Section: 20.2.2 [memory.syn] Status: C++20 Submitter: Jens Maurer Opened: 2019-10-10 Last modified: 2021-02-25

Priority: 0

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Discussion:

This issue was submitted as editorial issue cplusplus/draft#3181 but is considered non-editorial.

P0784R7, approved in Cologne, added "constexpr" markers to the overloads of destroy and destroy_n taking an ExecutionPolicy parameter. This seems to be in error; parallel algorithms should not be marked "constexpr". (None of the parallel algorithms in <algorithm> is marked "constexpr".)

[2019-11 Marked as 'Ready' during Monday issue prioritization in Belfast]

Proposed resolution:

This wording is relative to N4830.

1. Modify 20.2.2 [memory.syn], header <memory> synopsis, as indicated:

   namespace std {
     […]
     
     // 27.11.9 [specialized.destroy], destroy
     template<class T>
       constexpr void destroy_at(T* location);
     template<class ForwardIterator>
       constexpr void destroy(ForwardIterator first, ForwardIterator last);
     template<class ExecutionPolicy, class ForwardIterator>
       constexpr void destroy(ExecutionPolicy&& exec, // see 27.3.5 [algorithms.parallel.overloads]
                              ForwardIterator first, ForwardIterator last);
     template<class ForwardIterator, class Size>
       constexpr ForwardIterator destroy_n(ForwardIterator first, Size n);
     template<class ExecutionPolicy, class ForwardIterator, class Size>
       constexpr ForwardIterator destroy_n(ExecutionPolicy&& exec, // see 27.3.5 [algorithms.parallel.overloads]
                                           ForwardIterator first, Size n);  
     […]
   }