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<title>Issue 1012: reverse_iterator default ctor should value initialize</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++11">C++11</a> status.</em></p>
<h3 id="1012"><a href="lwg-defects.html#1012">1012</a>. <code>reverse_iterator</code> default ctor should value initialize</h3>
<p><b>Section:</b> 24.5.1.4 <a href="https://wg21.link/reverse.iter.cons">[reverse.iter.cons]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#reverse.iter.cons">issues</a> in [reverse.iter.cons].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++11">C++11</a> status.</p>
<p><b>Discussion:</b></p>

<p><b>Addresses UK 277</b></p>

<p>
The default constructor default-initializes current, rather than
value-initializes. This means that when Iterator corresponds to a
trivial type, the current member is left un-initialized, even when the
user explictly requests value intialization! At this point, it is not
safe to perform any operations on the reverse_iterator other than assign
it a new value or destroy it. Note that this does correspond to the
basic definition of a singular iterator.
</p>

<p><i>[
Summit:
]</i></p>


<blockquote><p>
Agree with option i.
</p></blockquote>

<p>
Related issue: <a href="lwg-closed.html#408" title="Is vector&lt;reverse_iterator&lt;char*&gt; &gt; forbidden? (Status: NAD Editorial)">408</a><sup><a href="https://cplusplus.github.io/LWG/issue408" title="Latest snapshot">(i)</a></sup>
</p>

<p><i>[
Batavia (2009-05):
]</i></p>

<blockquote><p>
We believe this should be revisited
in conjunction with issue <a href="lwg-closed.html#408" title="Is vector&lt;reverse_iterator&lt;char*&gt; &gt; forbidden? (Status: NAD Editorial)">408</a><sup><a href="https://cplusplus.github.io/LWG/issue408" title="Latest snapshot">(i)</a></sup>,
which nearly duplicates this issue.
Move to Open.
</p></blockquote>

<p><i>[
2009-07 post-Frankfurt:
]</i></p>


<blockquote>
<p>
Change "constructed" to "initialized" in two places in the proposed resolution.
</p>
<p>
Move to Tentatively Ready.
</p>
</blockquote>

<p><i>[
2009 Santa Cruz:
]</i></p>


<blockquote><p>
Moved to Ready for this meeting.
</p></blockquote>



<p id="res-1012"><b>Proposed resolution:</b></p>
<p>
Change  [reverse.iter.con]:
</p>

<blockquote><pre>
reverse_iterator();
</pre>
<blockquote><p>
-1- <i>Effects:</i> <del>Default</del> <ins>Value</ins> initializes <code>current</code>. Iterator
operations applied to the resulting iterator have defined behavior if and
only if the corresponding operations are defined on a <del>default constructed</del>
<ins>value initialized</ins>
iterator of type <code>Iterator</code>.
</p></blockquote>
</blockquote>

<p>
Change  [move.iter.op.const]:
</p>

<blockquote><pre>
move_iterator();
</pre>
<blockquote><p>
-1- <i>Effects:</i> Constructs a <code>move_iterator</code>, <del>default</del> <ins>value</ins>
initializing <code>current</code>.
<ins>Iterator
operations applied to the resulting iterator have defined behavior if and
only if the corresponding operations are defined on a
value initialized
iterator of type <code>Iterator</code>.</ins>
</p></blockquote>
</blockquote>






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