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<title>Issue 2350: min, max, and minmax should be constexpr</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++14">C++14</a> status.</em></p>
<h3 id="2350"><a href="lwg-defects.html#2350">2350</a>. <code>min</code>, <code>max</code>, and <code>minmax</code> should be <code>constexpr</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++14">C++14</a>
 <b>Submitter:</b> Ville Voutilainen <b>Opened:</b> 2013-12-15 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>1
</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++14">C++14</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Having <code>min</code>, <code>max</code>, and <code>minmax</code> <code>constexpr</code> 
was a large part of the motivation to allow reference-to-const arguments for 
<code>constexpr</code> functions as per 
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3039.pdf">N3039</a>.
Furthermore, <code>initializer_lists</code> are immutable and not-movable-from
for large part in order to allow using them in <code>constexpr</code> contexts
and other hoisting-optimizations. In <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3797.pdf">N3797</a> 
version of the draft none of these functions are <code>constexpr</code>, and they should be made
<code>constexpr</code>.
</p>



<p id="res-2350"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3797.</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 before <code>min_element</code>):</p>

<blockquote><pre>
template&lt;class T&gt; <ins>constexpr</ins> const T&amp; min(const T&amp; a, const T&amp; b);
template&lt;class T, class Compare&gt;
<ins>constexpr</ins> const T&amp; min(const T&amp; a, const T&amp; b, Compare comp);
[&hellip;]
template&lt;class T&gt;
<ins>constexpr</ins> T min(initializer_list&lt;T&gt; t);
template&lt;class T, class Compare>
<ins>constexpr</ins> T min(initializer_list&lt;T&gt; t, Compare comp);
[&hellip;]
template&lt;class T&gt; <ins>constexpr</ins> const T&amp; max(const T&amp; a, const T&amp; b);
template&lt;class T, class Compare&gt;
<ins>constexpr</ins> const T&amp; max(const T&amp; a, const T&amp; b, Compare comp);
[&hellip;]
template&lt;class T&gt;
<ins>constexpr</ins> T max(initializer_list&lt;T&gt; t);
template&lt;class T, class Compare>
<ins>constexpr</ins> T max(initializer_list&lt;T&gt; t, Compare comp);
[&hellip;]
template&lt;class T&gt; <ins>constexpr</ins> pair&lt;const T&amp;, const T&amp;&gt; minmax(const T&amp; a, const T&amp; b);
template&lt;class T, class Compare&gt;
<ins>constexpr</ins> pair&lt;const T&amp;, const T&amp;&gt; minmax(const T&amp; a, const T&amp; b, Compare comp);
[&hellip;]
template&lt;class T&gt;
<ins>constexpr</ins> pair&lt;T, T&gt; minmax(initializer_list&lt;T&gt; t);
template&lt;class T, class Compare>
<ins>constexpr</ins> pair&lt;T, T&gt; minmax(initializer_list&lt;T&gt; t, Compare comp);
</pre></blockquote>
</li>

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