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<title>Issue 2323: vector::resize(n, t)'s specification should be simplified</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="2323"><a href="lwg-defects.html#2323">2323</a>. <code>vector::resize(n, t)</code>'s specification should be simplified</h3>
<p><b>Section:</b> 23.3.13.3 <a href="https://wg21.link/vector.capacity">[vector.capacity]</a>, 23.3.5.3 <a href="https://wg21.link/deque.capacity">[deque.capacity]</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#vector.capacity">active issues</a> in [vector.capacity].</p>
<p><b>View all other</b> <a href="lwg-index.html#vector.capacity">issues</a> in [vector.capacity].</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>
First, 23.3.5.3 <a href="https://wg21.link/deque.capacity">[deque.capacity]</a>/4 and 23.3.13.3 <a href="https://wg21.link/vector.capacity">[vector.capacity]</a>/16 say that <code>resize(size_type sz, const T&amp; c)</code> 
"<i>Requires:</i> <code>T</code> shall be <code>MoveInsertable</code> into <code>*this</code> and <code>CopyInsertable</code> into <code>*this</code>."  
The <code>CopyInsertable</code> requirement is correct (because <code>sz</code> might be <code>size() + 2</code> or more), but the 
<code>MoveInsertable</code> requirement is redundant due to 23.2.2 <a href="https://wg21.link/container.requirements.general">[container.requirements.general]</a>/13: "<code>T</code> is 
<code>CopyInsertable</code> into <code>X</code> means that, in addition to <code>T</code> being <code>MoveInsertable</code> into <code>X</code>, the [...]".  
(LWG <a href="lwg-defects.html#2033" title="Preconditions of reserve, shrink_to_fit, and resize functions (Status: C++14)">2033</a><sup><a href="https://cplusplus.github.io/LWG/issue2033" title="Latest snapshot">(i)</a></sup>'s resolution said that this was "not redundant, because <code>CopyInsertable</code> is not necessarily a refinement 
of <code>MoveInsertable</code>" which was true at the time, but then LWG <a href="lwg-defects.html#2177" title="Requirements on Copy&#47;MoveInsertable (Status: C++14)">2177</a><sup><a href="https://cplusplus.github.io/LWG/issue2177" title="Latest snapshot">(i)</a></sup>'s resolution made it a refinement.)
<p/>
Second, 23.3.13.3 <a href="https://wg21.link/vector.capacity">[vector.capacity]</a>/17 says "<i>Remarks:</i> If an exception is thrown other than by the move constructor of a 
non-<code>CopyInsertable</code> <code>T</code> there are no effects." This is confusing because <code>T</code> is required to be 
<code>CopyInsertable</code>. (/14 says the same thing for <code>resize(size_type sz)</code>, where it is correct because that overload 
requires only <code>MoveInsertable</code> and <code>DefaultInsertable</code>.)
</p>

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




<p id="res-2323"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3691.</p>

<ol>
<li><p>Edit 23.3.5.3 <a href="https://wg21.link/deque.capacity">[deque.capacity]</a>/4 as indicated:</p>

<blockquote><pre>
void resize(size_type sz, const T&amp; c);
</pre><blockquote>
<p>
[&hellip;]
<p/>
-4- <i>Requires:</i> <code>T</code> shall be <del><code>MoveInsertable</code> into <code>*this</code> and</del> <code>CopyInsertable</code> into 
<code>*this</code>.
</p>
</blockquote></blockquote>
</li>

<li><p>Edit 23.3.13.3 <a href="https://wg21.link/vector.capacity">[vector.capacity]</a>/16+17 as indicated:</p>

<blockquote><pre>
void resize(size_type sz, const T&amp; c);
</pre><blockquote>
<p>
[&hellip;]
<p/>
-16- <i>Requires:</i> <code>T</code> shall be <del><code>MoveInsertable</code> into <code>*this</code> and</del> <code>CopyInsertable</code> into 
<code>*this</code>.
<p/>
-17- <i>Remarks:</i> If an exception is thrown <del>other than by the move constructor of a non-<code>CopyInsertable</code> <code>T</code></del> 
there are no effects.
</p>
</blockquote></blockquote>
</li>

</ol>






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