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<title>Issue 3506: Missing allocator-extended constructors for 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#C++23">C++23</a> status.</em></p>
<h3 id="3506"><a href="lwg-defects.html#3506">3506</a>. Missing allocator-extended constructors for <code>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#C++23">C++23</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2020-11-21 <b>Last modified:</b> 2023-11-22</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#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>priority_queue</code> has two constructor templates taking a pair of input
iterators in addition to a comparator and a container, but it does not have
allocator-extended constructors corresponding to these constructor templates:
</p>
<blockquote><pre>
template&lt;class InputIterator&gt;
  priority_queue(InputIterator first, InputIterator last, const Compare&amp; x,
                 const Container&amp;);
template&lt;class InputIterator&gt;
  priority_queue(InputIterator first, InputIterator last,
                 const Compare&amp; x = Compare(), Container&amp;&amp; = Container());
</pre></blockquote>

<p><i>[2020-11-29; Reflector prioritization]</i></p>

<p>
Set priority to 3 during reflector discussions. It has been pointed out that this issue
is related to LWG <a href="lwg-defects.html#1199" title="Missing extended copy constructor in container adaptors (Status: C++11)">1199</a><sup><a href="https://cplusplus.github.io/LWG/issue1199" title="Latest snapshot">(i)</a></sup>, LWG <a href="lwg-defects.html#2210" title="Missing allocator-extended constructor for allocator-aware containers (Status: C++14)">2210</a><sup><a href="https://cplusplus.github.io/LWG/issue2210" title="Latest snapshot">(i)</a></sup>, and LWG <a href="lwg-active.html#2713" title="More missing allocator-extended constructors for unordered containers (Status: New)">2713</a><sup><a href="https://cplusplus.github.io/LWG/issue2713" title="Latest snapshot">(i)</a></sup>.
</p>

<p><i>[2021-02-17 Tim adds PR]</i></p>


<p><i>[2021-02-26; LWG telecon]</i></p>

<p>
Set status to Tentatively Ready after discussion and poll.
<table>
<tr><th>F</th><th>A</th><th>N</th></tr>
<tr><td>11</td><td>0</td><td>0</td></tr>
</table>
</p>

<p><i>[2021-06-07 Approved at June 2021 virtual plenary. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3506"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4878">N4878</a>.
</p>

<ol>
<li><p>Add the following paragraph at the end of 23.6.1 <a href="https://wg21.link/container.adaptors.general">[container.adaptors.general]</a>:</p>
<blockquote>
<p>
<ins>-6- The exposition-only alias template <i><code>iter-value-type</code></i> defined in
23.3.1 <a href="https://wg21.link/sequences.general">[sequences.general]</a> may appear in deduction guides for container adaptors.</ins>
</p>
</blockquote>
</li>
<li><p>Modify 23.6.4 <a href="https://wg21.link/priority.queue">[priority.queue]</a>, class template <code>priority_queue</code> synopsis, as indicated:</p>
<blockquote>
<pre>
namespace std {
  template&lt;class T, class Container = vector&lt;T&gt;,
            class Compare = less&lt;typename Container::value_type&gt;&gt;
  class priority_queue {

  // [&hellip;]

  public:
    priority_queue() : priority_queue(Compare()) {}
    explicit priority_queue(const Compare&amp; x) : priority_queue(x, Container()) {}
    priority_queue(const Compare&amp; x, const Container&amp;);
    priority_queue(const Compare&amp; x, Container&amp;&amp;);
    template&lt;class InputIterator&gt;
      priority_queue(InputIterator first, InputIterator last, const Compare&amp; x,
                      const Container&amp;);
    template&lt;class InputIterator&gt;
      priority_queue(InputIterator first, InputIterator last,
                      const Compare&amp; x = Compare(), Container&amp;&amp; = Container());
    template&lt;class Alloc&gt; explicit priority_queue(const Alloc&amp;);
    template&lt;class Alloc&gt; priority_queue(const Compare&amp;, const Alloc&amp;);
    template&lt;class Alloc&gt; priority_queue(const Compare&amp;, const Container&amp;, const Alloc&amp;);
    template&lt;class Alloc&gt; priority_queue(const Compare&amp;, Container&amp;&amp;, const Alloc&amp;);
    template&lt;class Alloc&gt; priority_queue(const priority_queue&amp;, const Alloc&amp;);
    template&lt;class Alloc&gt; priority_queue(priority_queue&amp;&amp;, const Alloc&amp;);
<ins>    template&lt;class InputIterator, class Alloc&gt;
      priority_queue(InputIterator, InputIterator, const Alloc&amp;);
    template&lt;class InputIterator, class Alloc&gt;
      priority_queue(InputIterator, InputIterator, const Compare&amp;, const Alloc&amp;);
    template&lt;class InputIterator, class Alloc&gt;
      priority_queue(InputIterator, InputIterator, const Compare&amp;, const Container&amp;, const Alloc&amp;);
    template&lt;class InputIterator, class Alloc&gt;
      priority_queue(InputIterator, InputIterator, const Compare&amp;, Container&amp;&amp;, const Alloc&amp;);</ins>

  // [&hellip;]

  };

  template&lt;class Compare, class Container&gt;
    priority_queue(Compare, Container)
      -&gt; priority_queue&lt;typename Container::value_type, Container, Compare&gt;;

  template&lt;class InputIterator,
            class Compare = less&lt;<del>typename iterator_traits</del><ins><i>iter-value-type</i></ins>&lt;InputIterator&gt;<del>::value_type</del>&gt;,
            class Container = vector&lt;<del>typename iterator_traits</del><ins><i>iter-value-type</i></ins>&lt;InputIterator&gt;<del>::value_type</del>&gt;&gt;
    priority_queue(InputIterator, InputIterator, Compare = Compare(), Container = Container())
      -&gt; priority_queue&lt;<del>typename iterator_traits</del><ins><i>iter-value-type</i></ins>&lt;InputIterator&gt;<del>::value_type</del>, Container, Compare&gt;;

  template&lt;class Compare, class Container, class Allocator&gt;
    priority_queue(Compare, Container, Allocator)
      -&gt; priority_queue&lt;typename Container::value_type, Container, Compare&gt;;

<ins>  template&lt;class InputIterator, class Allocator&gt;
    priority_queue(InputIterator, InputIterator, Allocator)
      -&gt; priority_queue&lt;<i>iter-value-type</i>&lt;InputIterator&gt;,
                        vector&lt;<i>iter-value-type</i>&lt;InputIterator&gt;, Allocator&gt;,
                        less&lt;<i>iter-value-type</i>&lt;InputIterator&gt;&gt;&gt;;

  template&lt;class InputIterator, class Compare, class Allocator&gt;
    priority_queue(InputIterator, InputIterator, Compare, Allocator)
      -&gt; priority_queue&lt;<i>iter-value-type</i>&lt;InputIterator&gt;,
                        vector&lt;<i>iter-value-type</i>&lt;InputIterator&gt;, Allocator&gt;, Compare&gt;;

  template&lt;class InputIterator, class Compare, class Container, class Allocator&gt;
    priority_queue(InputIterator, InputIterator, Compare, Container, Allocator)
      -&gt; priority_queue&lt;typename Container::value_type, Container, Compare&gt;;</ins>

  // [&hellip;]
}
</pre>
</blockquote>
</li>

<li><p>Add the following paragraphs to 23.6.4.3 <a href="https://wg21.link/priqueue.cons.alloc">[priqueue.cons.alloc]</a>:</p>
<blockquote>
<pre>
template&lt;class InputIterator, class Alloc&gt;
  priority_queue(InputIterator first, InputIterator last, const Alloc&amp; a);
</pre>
<blockquote>
<p>-?- <i>Effects:</i> Initializes <code>c</code> with <code>first</code> as the first argument, <code>last</code> as
the second argument, and <code>a</code> as the third argument, and value-initializes <code>comp</code>;
calls <code>make_heap(c.begin(), c.end(), comp)</code>. </p>
</blockquote>
<pre>
template&lt;class InputIterator, class Alloc&gt;
  priority_queue(InputIterator first, InputIterator last, const Compare&amp; compare, const Alloc&amp; a);
</pre>
<blockquote>
<p>-?- <i>Effects:</i> Initializes <code>c</code> with <code>first</code> as the first argument, <code>last</code> as
the second argument, and <code>a</code> as the third argument, and initializes <code>comp</code> with <code>compare</code>;
calls <code>make_heap(c.begin(), c.end(), comp)</code>. </p>
</blockquote>
<pre>
template&lt;class InputIterator, class Alloc&gt;
  priority_queue(InputIterator first, InputIterator last, const Compare&amp; compare, const Container&amp; cont, const Alloc&amp; a);
</pre>
<blockquote>
<p>-?- <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>; calls <code>c.insert(c.end(), first, last)</code>;
and finally calls <code>make_­heap(c.begin(), c.end(), comp)</code>. </p>
</blockquote>
<pre>
template&lt;class InputIterator, class Alloc&gt;
  priority_queue(InputIterator first, InputIterator last, const Compare&amp; compare, Container&amp;&amp; cont, const Alloc&amp; a);
</pre>
<blockquote>
<p>-?- <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>; calls <code>c.insert(c.end(), first, last)</code>;
and finally calls <code>make_­heap(c.begin(), c.end(), comp)</code>. </p>
</blockquote>
</blockquote>
</li>
</ol>





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