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### 3303. Bad "`constexpr`" marker for `destroy/destroy_n`

Section: 20.10.2 [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 20.10.2 [memory.syn], header `<memory>` synopsis, as indicated:

   >     namespace std {
   >       […]

   >       // 25.11.9 [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 25.3.5 [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 25.3.5 [algorithms.parallel.overloads]
   >                                             ForwardIterator first, Size n);
   >       […]
   >     }