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<title>Issue 3303: Bad "constexpr" marker for destroy/destroy_n</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#C++20">C++20</a> status.</em></p>
<h3 id="3303"><a href="lwg-defects.html#3303">3303</a>. Bad "<code>constexpr</code>" marker for <code>destroy/destroy_n</code></h3>
<p><b>Section:</b> 20.2.2 <a href="https://wg21.link/memory.syn">[memory.syn]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Jens Maurer <b>Opened:</b> 2019-10-10 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#memory.syn">issues</a> in [memory.syn].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
This issue was submitted as editorial issue 
<a href="https://github.com/cplusplus/draft/issues/3181">cplusplus/draft#3181</a> but is 
considered non-editorial.
<p/>
<a href="https://wg21.link/p0784r7">P0784R7</a>, approved in Cologne, added "<code>constexpr</code>" markers to
the overloads of <code>destroy</code> and <code>destroy_n</code> taking an <code>ExecutionPolicy</code> 
parameter.  This seems to be in error; parallel algorithms should not be marked "<code>constexpr</code>".
(None of the parallel algorithms in <code>&lt;algorithm&gt;</code> is marked "<code>constexpr</code>".)
</p>
<p><i>[2019-11 Marked as 'Ready' during Monday issue prioritization in Belfast]</i></p>



<p id="res-3303"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4830">N4830</a>.</p>

<ol>
<li><p>Modify 20.2.2 <a href="https://wg21.link/memory.syn">[memory.syn]</a>, header <code>&lt;memory&gt;</code> synopsis, as indicated:</p>

<blockquote>
<pre>
namespace std {
  [&hellip;]
  
  <i>// 26.11.9 <a href="https://wg21.link/specialized.destroy">[specialized.destroy]</a>, destroy</i>
  template&lt;class T&gt;
    constexpr void destroy_at(T* location);
  template&lt;class ForwardIterator&gt;
    constexpr void destroy(ForwardIterator first, ForwardIterator last);
  template&lt;class ExecutionPolicy, class ForwardIterator&gt;
    <del>constexpr</del> void destroy(ExecutionPolicy&amp;&amp; exec, <i>// see 26.3.5 <a href="https://wg21.link/algorithms.parallel.overloads">[algorithms.parallel.overloads]</a></i>
                           ForwardIterator first, ForwardIterator last);
  template&lt;class ForwardIterator, class Size&gt;
    constexpr ForwardIterator destroy_n(ForwardIterator first, Size n);
  template&lt;class ExecutionPolicy, class ForwardIterator, class Size&gt;
    <del>constexpr</del> ForwardIterator destroy_n(ExecutionPolicy&amp;&amp; exec, <i>// see 26.3.5 <a href="https://wg21.link/algorithms.parallel.overloads">[algorithms.parallel.overloads]</a></i>
                                        ForwardIterator first, Size n);  
  [&hellip;]
}
</pre>
</blockquote>
</li>

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