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<title>Issue 2537: Constructors for priority_queue taking allocators should call make_heap</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="2537"><a href="lwg-defects.html#2537">2537</a>. Constructors for <code>priority_queue</code> taking allocators should call <code>make_heap</code></h3>
<p><b>Section:</b> 23.6.4.3 <a href="https://wg21.link/priqueue.cons.alloc">[priqueue.cons.alloc]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Eric Schmidt <b>Opened:</b> 2015-09-19 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>0
</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>
<code>priority_queue</code> constructors taking both <code>Container</code> and <code>Alloc</code> arguments should 
finish by calling <code>make_heap</code>, just as with the constructors that do not have allocator parameters.
<p/>
The current reading of 23.6.4.3 <a href="https://wg21.link/priqueue.cons.alloc">[priqueue.cons.alloc]</a>, if followed strictly, would effectively require calling 
code to ensure that the container argument is already a heap, which is probably not what was intended.
</p>

<p><i>[2015-10, Kona issue prioritization]</i></p>

<p>Priority 0, move to Ready</p>


<p id="res-2537"><b>Proposed resolution:</b></p>
<p>This wording is relative to N4527.</p>

<ol>
<li><p>Change 23.6.4.3 <a href="https://wg21.link/priqueue.cons.alloc">[priqueue.cons.alloc]</a> as indicated:</p>
<blockquote>
<pre>
template &lt;class Alloc&gt;
priority_queue(const Compare&amp; compare, const Container&amp; cont, const Alloc&amp; a);
</pre>
<blockquote>
<p>
-4- <i>Effects</i>: Initializes <code>c</code> with <code>cont</code> as the first argument and <code>a</code> as the second 
argument, and initializes <code>comp</code> with <code>compare</code><ins>; calls <code>make_heap(c.begin(), c.end(), comp)</code></ins>.
</p>
</blockquote>
<pre>
template &lt;class Alloc&gt;
priority_queue(const Compare&amp; compare, Container&amp;&amp; cont, const Alloc&amp; a);
</pre>
<blockquote>
<p>
-5- <i>Effects</i>: Initializes <code>c</code> with <code>std::move(cont)</code> as the first argument and <code>a</code> as the second 
argument, and initializes <code>comp</code> with <code>compare</code><ins>; calls <code>make_heap(c.begin(), c.end(), comp)</code></ins>.
</p>
</blockquote>
</blockquote>
</li>
</ol>





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