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<title>Issue 2369: constexpr max(initializer_list) vs max_element</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++17">C++17</a> status.</em></p>
<h3 id="2369"><a href="lwg-defects.html#2369">2369</a>. <code>constexpr max(initializer_list)</code> vs <code>max_element</code></h3>
<p><b>Section:</b> 26.8.9 <a href="https://wg21.link/alg.min.max">[alg.min.max]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Marc Glisse <b>Opened:</b> 2014-02-21 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>3
</p>
<p><b>View other</b> <a href="lwg-index-open.html#alg.min.max">active issues</a> in [alg.min.max].</p>
<p><b>View all other</b> <a href="lwg-index.html#alg.min.max">issues</a> in [alg.min.max].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++17">C++17</a> status.</p>
<p><b>Discussion:</b></p>
<p>
As part of the resolution for LWG issue <a href="lwg-defects.html#2350" title="min, max, and minmax should be constexpr (Status: C++14)">2350</a><sup><a href="https://cplusplus.github.io/LWG/issue2350" title="Latest snapshot">(i)</a></sup>, <code>max(initializer_list)</code> was marked as <code>constexpr</code>. Looking 
at two implementations of this function (libstdc++ and libc++), both implement it in terms of <code>max_element</code>, which is <em>not</em> 
marked as <code>constexpr</code>. This is inconsistent and forces some small amount of code duplication in the implementation. Unless we 
remove <code>constexpr</code> from this overload of <code>max</code>, I believe we should add <code>constexpr</code> to <code>max_element</code>.
</p>

<p><i>[2015-02 Cologne]</i></p>

<p>
AM: Can we implement this with the C++14 <code>constexpr</code> rules? JM: Yes. AM: Ready? [Yes]
<p/>
Accepted.
</p>



<p id="res-2369"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3936.</p>

<ol>
<li><p>In 26.1 <a href="https://wg21.link/algorithms.general">[algorithms.general]</a>, header <code>&lt;algorithm&gt;</code> synopsis, and 26.8.9 <a href="https://wg21.link/alg.min.max">[alg.min.max]</a>, change as 
indicated (add <code>constexpr</code> to every signature from the first <code>min_element</code> to the second <code>minmax_element</code>)::</p>

<blockquote>
<pre>
template&lt;class ForwardIterator&gt;
<ins>constexpr</ins> ForwardIterator min_element(ForwardIterator first, ForwardIterator last);
template&lt;class ForwardIterator, class Compare&gt;
<ins>constexpr</ins> ForwardIterator min_element(ForwardIterator first, ForwardIterator last,
                                      Compare comp);
[&hellip;]
template&lt;class ForwardIterator&gt;
<ins>constexpr</ins> ForwardIterator max_element(ForwardIterator first, ForwardIterator last);
template&lt;class ForwardIterator, class Compare&gt;
<ins>constexpr</ins> ForwardIterator max_element(ForwardIterator first, ForwardIterator last,
                                      Compare comp);
[&hellip;]
template&lt;class ForwardIterator&gt;
<ins>constexpr</ins> pair&lt;ForwardIterator, ForwardIterator&gt;
minmax_element(ForwardIterator first, ForwardIterator last);
template&lt;class ForwardIterator, class Compare&gt;
<ins>constexpr</ins> pair&lt;ForwardIterator, ForwardIterator&gt;
minmax_element(ForwardIterator first, ForwardIterator last, Compare comp);
</pre>
</blockquote>
</li>

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