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<title>Issue 2105: Inconsistent requirements on const_iterator's value_type</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="2105"><a href="lwg-defects.html#2105">2105</a>. Inconsistent requirements on <code>const_iterator</code>'s <code>value_type</code></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> Jeffrey Yasskin <b>Opened:</b> 2011-11-28 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</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>
In the FDIS, Table 96 specifies <code>X::const_iterator</code> as a "constant iterator type 
whose value type is <code>T</code>". However, Table 97 specifies <code>X::const_reverse_iterator</code> 
as an "iterator type whose value type is <code>const T</code>" and which is defined as 
<code>reverse_iterator&lt;const_iterator&gt;</code>. But <code>reverse_iterator::value_type</code> is 
just "<code>typename iterator_traits&lt;Iterator&gt;::value_type</code>" 24.5.1.2 <a href="https://wg21.link/reverse.iterator">[reverse.iterator]</a>, 
so <code>const_iterator</code> and <code>const_reverse_iterator</code> must have the same <code>value_type</code>.
</p>
<p>
The resolution to issue <a href="lwg-defects.html#322" title="iterator and const_iterator should have the same value type (Status: CD1)">322</a><sup><a href="https://cplusplus.github.io/LWG/issue322" title="Latest snapshot">(i)</a></sup> implies that
<code>const_reverse_iterator</code> should change.
</p>

<p><i>[2012, Kona]</i></p>

<p>
Move to Ready.
</p>

<p><i>[2012, Portland: applied to WP]</i></p>




<p id="res-2105"><b>Proposed resolution:</b></p>
<p>This wording is relative to the FDIS.</p>

<p>Change Table 97 &mdash; "Reversible container requirements" as indicated</p>

<table border="1">
<caption>Table 97 &mdash; Reversible container requirements</caption>
<tr>
<th>Expression</th>
<th>Return type</th>
<th>Assertion&#47;note pre-&#47;post-condition</th>
<th>Complexity</th>
</tr> 

<tr>
<td>
<code>X::reverse_-<br/>
iterator</code>
</td>
<td>
iterator type whose value type<br/>
is <code>T</code>
</td>
<td>
<code>reverse_iterator&lt;iterator&gt;</code>
</td>
<td>
compile time
</td>
</tr>

<tr>
<td>
<code>X::const_-<br/>
reverse_-<br/>
iterator</code>
</td>
<td>
<ins>constant</ins> iterator type whose value type<br/>
is <code><del>const</del> T</code>
</td>
<td>
<code>reverse_iterator&lt;const_iterator&gt;</code>
</td>
<td>
compile time
</td>
</tr>
</table>







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