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<title>Issue 3514: stacktrace should add type alias pmr::stacktrace</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#Resolved">Resolved</a> status.</em></p>
<h3 id="3514"><a href="lwg-defects.html#3514">3514</a>. <code>stacktrace</code> should add type alias <code>pmr::stacktrace</code></h3>
<p><b>Section:</b> 19.6.2 <a href="https://wg21.link/stacktrace.syn">[stacktrace.syn]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Hiroaki Ando <b>Opened:</b> 2021-01-11 <b>Last modified:</b> 2021-10-23</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#stacktrace.syn">issues</a> in [stacktrace.syn].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>std::stacktrace</code> is almost <code>std::vector&lt;stacktrace_entry&gt;</code>. This
makes it an obvious candidate to define an alias for <code>std::polymorphic_allocator</code>.
<p/>
<b>Daniel:</b>
<p/>
It should be pointed out that a theoretically possible (additional) template alias
</p>
<blockquote><pre>
namespace pmr {
  template&lt;class T&gt;
    using basic_stacktrace = std::basic_stacktrace&lt;polymorphic_allocator&lt;T&gt;&gt;;
}
</pre></blockquote>
<p>
&mdash; albeit it would seem a natural choice when comparing with existing <code>pmr</code> typedef
additions &mdash; would not provide any advantage for the user, because template parameter
<code>T</code> would essentially need to be constrained to be equal to <code>std::stacktrace_entry</code>.
</p>

<p><i>[2021-03-12; Reflector poll]</i></p>

<p>
Set priority to 3 and status to LEWG following reflector poll.
</p>
<p><a href="https://wg21.link/p2301">P2301</a> would resolve this.</p>

<p><i>[2021-10-23 Resolved by the adoption of <a href="https://wg21.link/P2301R1" title=" Add a pmr alias for std::stacktrace">P2301R1</a> at the October 2021 plenary. Status changed: Tentatively Resolved &rarr; Resolved.]</i></p>



<p id="res-3514"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4878">N4878</a>.
</p>

<ol>
<li><p>Modify 19.6.2 <a href="https://wg21.link/stacktrace.syn">[stacktrace.syn]</a>, header <code>&lt;stacktrace&gt;</code> synopsis, as indicated:</p>

<blockquote><pre>
namespace std {
  <i>// 19.6.3 <a href="https://wg21.link/stacktrace.entry">[stacktrace.entry]</a>, class stacktrace_entry</i>
  class stacktrace_entry;

  <i>// 19.6.4 <a href="https://wg21.link/stacktrace.basic">[stacktrace.basic]</a>, class template basic_stacktrace</i>
  template&lt;class Allocator&gt;
  class basic_stacktrace;

  // basic_stacktrace typedef names
  using stacktrace = basic_stacktrace&lt;allocator&lt;stacktrace_entry&gt;&gt;;

  [&hellip;]

  <i>// 19.6.6 <a href="https://wg21.link/stacktrace.basic.hash">[stacktrace.basic.hash]</a>, hash support</i>
  template&lt;class T&gt; struct hash;
  template&lt;&gt; struct hash&lt;stacktrace_entry&gt;;
  template&lt;class Allocator&gt; struct hash&lt;basic_stacktrace&lt;Allocator&gt;&gt;;

  <ins>namespace pmr {
    using stacktrace = std::basic_stacktrace&lt;polymorphic_allocator&lt;stacktrace_entry&gt;&gt;;
  }</ins>
}
</pre></blockquote>
</li>
</ol>





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