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<title>Issue 3349: Missing __cpp_lib_constexpr_complex for P0415R1</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="3349"><a href="lwg-defects.html#3349">3349</a>. Missing <code>__cpp_lib_constexpr_complex</code> for P0415R1</h3>
<p><b>Section:</b> 17.3.2 <a href="https://wg21.link/version.syn">[version.syn]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2019-12-04 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View other</b> <a href="lwg-index-open.html#version.syn">active issues</a> in [version.syn].</p>
<p><b>View all other</b> <a href="lwg-index.html#version.syn">issues</a> in [version.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>
<a href="https://wg21.link/p1902r1">P1902R1</a> "Missing feature-test macros 2017-2019", accepted in Belfast, said:
</p>
<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
<p>
[<a href="https://wg21.link/p0415r1">P0415R1</a>] (Constexpr for <code>std::complex</code>): this paper proposes to 
introduce the macro <code>__cpp_lib_constexpr_complex</code>. That is, introducing a new macro for this header.
</p>
</blockquote>
<p>
However, <code>__cpp_lib_constexpr_complex</code> wasn't mentioned in the Wording section, and doesn't appear 
in the latest WP <a href="https://wg21.link/n4842">N4842</a>.
<p/>
<a href="https://wg21.link/p0415r1">P0415R1</a> was accepted in Albuquerque (November 2017), and the paper itself 
said "For the purposes of SG10, we recommend the feature-testing macro name <code>__cpp_lib_constexpr_complex</code>.", 
so this has been accepted and then overlooked by WG21 twice.
</p>

<p><i>[2019-12-12 Issue Prioritization]</i></p>

<p>Status to Tentatively Ready and priority to 0 after twelve positive votes on the reflector.</p>


<p id="res-3349"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4842">N4842</a>.</p>

<ol>
<li><p>Modify 17.3.2 <a href="https://wg21.link/version.syn">[version.syn]</a> p2 as indicated:</p>
<blockquote>
<pre>
[&hellip;]
#define __cpp_lib_constexpr_algorithms    201806L <i>// also in &lt;algorithm&gt;</i>
<ins>#define __cpp_lib_constexpr_complex       201711L <i>// also in &lt;complex&gt;</i></ins>
#define __cpp_lib_constexpr_dynamic_alloc 201907L <i>// also in &lt;memory&gt;</i>
[&hellip;]
</pre>
</blockquote>
</li>

</ol>




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