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<title>Issue 2320: select_on_container_copy_construction() takes allocators, not containers</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="2320"><a href="lwg-defects.html#2320">2320</a>. <code>select_on_container_copy_construction()</code> takes allocators, not containers</h3>
<p><b>Section:</b> 23.2.2 <a href="https://wg21.link/container.requirements.general">[container.requirements.general]</a> <b>Status:</b> <a href="lwg-active.html#C++14">C++14</a>
 <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2013-09-21 <b>Last modified:</b> 2017-07-05</p>
<p><b>Priority: </b>0
</p>
<p><b>View other</b> <a href="lwg-index-open.html#container.requirements.general">active issues</a> in [container.requirements.general].</p>
<p><b>View all other</b> <a href="lwg-index.html#container.requirements.general">issues</a> in [container.requirements.general].</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>
23.2.2 <a href="https://wg21.link/container.requirements.general">[container.requirements.general]</a>/7 says "Copy constructors for these container types obtain an allocator by calling 
<code>allocator_traits&lt;allocator_type&gt;::select_on_container_copy_construction</code> on their first parameters."  However, 
20.2.9.3 <a href="https://wg21.link/allocator.traits.members">[allocator.traits.members]</a>/8 says that this takes <code>const Alloc&amp;</code>, not a container.  
23.2.2 <a href="https://wg21.link/container.requirements.general">[container.requirements.general]</a>/7 goes on to say "Move constructors obtain an allocator by move construction from 
the allocator belonging to the container being moved." so we can follow that wording.
</p>

<p><i>[Issaquah 2014-02-11: Move to Immediate]</i></p>




<p id="res-2320"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3691.</p>

<ol>
<li><p>In 23.2.2 <a href="https://wg21.link/container.requirements.general">[container.requirements.general]</a>/7 change as indicated:</p>

<blockquote><p>
-7- Unless otherwise specified, all containers defined in this clause obtain memory using an allocator (see 17.6.3.5).
Copy constructors for these container types obtain an allocator by calling 
<code>allocator_traits&lt;allocator_type&gt;::select_on_container_copy_construction</code> on <del>their first 
parameters</del><ins>the allocator belonging to the container being copied</ins>. 
Move constructors obtain an allocator by move construction from the allocator belonging to the container being moved. [&hellip;]
</p></blockquote>
</li>

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