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<title>Issue 3723: priority_queue::push_range needs to append_range</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="3723"><a href="lwg-defects.html#3723">3723</a>. <code>priority_queue::push_range</code> needs to <code>append_range</code></h3>
<p><b>Section:</b> 23.6.4.4 <a href="https://wg21.link/priqueue.members">[priqueue.members]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Casey Carter <b>Opened:</b> 2022-06-20 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>2
</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>
The <code>push_range</code> members of the <code>queue</code> (23.6.3.4 <a href="https://wg21.link/queue.mod">[queue.mod]</a>) and 
<code>stack</code> (23.6.6.5 <a href="https://wg21.link/stack.mod">[stack.mod]</a>) container adaptors are both specified as 
"<i>Effects</i>: Equivalent to <code>c.append_range(std::forward&lt;R&gt;(rg))</code> if that 
is a valid expression, otherwise <code>ranges::copy(rg, back_inserter(c))</code>.". For 
<code>priority_queue</code>, however, we have instead (23.6.4.4 <a href="https://wg21.link/priqueue.members">[priqueue.members]</a>):
</p>
<blockquote><p>
-3- <i>Effects</i>: Insert all elements of <code>rg</code> in <code>c</code>.
<p/>
-4- <i>Postconditions</i>: <code>is_heap(c.begin(), c.end(), comp)</code> is <code>true</code>.
</p></blockquote>
<p>
Since <code>append_range</code> isn't one of the operations required of the underlying container, 
"Insert all elements of <code>rg</code>" must be implemented via potentially less efficient means. 
It would be nice if this <code>push_back</code> could take advantage of <code>append_range</code> 
when it's available just as do the other two overloads.
</p>

<p><i>[2022-07-08; Reflector poll]</i></p>

<p>
Set priority to 2 after reflector poll.
</p>

<p><i>[Issaquah 2023-02-08; LWG]</i></p>

<p>Unanimous consent to move to Immediate.</p>

<p><i>[2023-02-13 Approved at February 2023 meeting in Issaquah. Status changed: Immediate &rarr; WP.]</i></p>



<p id="res-3723"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4910" title=" Working Draft, Standard for Programming Language C++">N4910</a>.
</p>

<ol>
<li><p>Modify 23.6.4.4 <a href="https://wg21.link/priqueue.members">[priqueue.members]</a> as indicated:</p>

<blockquote>
<pre>
template&lt;<i>container-compatible-range</i>&lt;T&gt; R&gt;
  void push_range(R&amp;&amp; rg);
</pre>
<blockquote>
<p>
-3- <i>Effects</i>: Insert<ins>s</ins> all elements of <code>rg</code> in <code>c</code> <ins>via 
<code>c.append_range(std::forward&lt;R&gt;(rg))</code> if that is a valid expression, or 
<code>ranges::copy(rg, back_inserter(c))</code> otherwise. Then restores the heap property as if 
by <code>make_heap(c.begin(), c.end(), comp)</code></ins>.
<p/>
-4- <i>Postconditions</i>: <code>is_heap(c.begin(), c.end(), comp)</code> is <code>true</code>. 
</p>
</blockquote>
</blockquote>
</li>

</ol>





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