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<title>Issue 3189: Missing requirement for std::priority_queue</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#New">New</a> status.</em></p>
<h3 id="3189"><a href="lwg-active.html#3189">3189</a>. Missing requirement for <code>std::priority_queue</code></h3>
<p><b>Section:</b> 23.6.4 <a href="https://wg21.link/priority.queue">[priority.queue]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2019-02-21 <b>Last modified:</b> 2019-03-05</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#priority.queue">issues</a> in [priority.queue].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
We don't require that the <code>Compare</code> template parameter can be invoked with arguments of the queue's value type. 
It seems like something we can use <i>Mandates:</i> for, since it'll be ill-formed otherwise. Something like 
<code>is_invocable_r_v&lt;bool, Compare&amp;, value_type&amp;, value_type&amp;&gt;</code>.
<p/>
This might also apply to the <code>Compare</code> parameter for the <code>merge</code> and <code>sort</code> functions of 
<code>forward_list</code> and <code>list</code>.
</p>

<p><i>[2019-03-05 Priority set to 3 after reflector discussion]</i></p>



<p id="res-3189"><b>Proposed resolution:</b></p>




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