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<title>Issue 872: move_iterator::operator[] has wrong return 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++11">C++11</a> status.</em></p>
<h3 id="872"><a href="lwg-defects.html#872">872</a>. <code>move_iterator::operator[]</code> has wrong return type</h3>
<p><b>Section:</b> 24.5.4.6 <a href="https://wg21.link/move.iter.elem">[move.iter.elem]</a> <b>Status:</b> <a href="lwg-active.html#C++11">C++11</a>
 <b>Submitter:</b> Doug Gregor <b>Opened:</b> 2008-08-21 <b>Last modified:</b> 2021-06-06</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#move.iter.elem">issues</a> in [move.iter.elem].</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>
<code>move_iterator</code>'s <code>operator[]</code> is declared as:
</p>

<blockquote><pre>
reference operator[](difference_type n) const;
</pre></blockquote>

<p>
This has the same problem that <code>reverse_iterator</code>'s <code>operator[]</code> used to
have: if the underlying iterator's <code>operator[]</code> returns a proxy, the
implicit conversion to <code>value_type&amp;&amp;</code> could end up referencing a temporary
that has already been destroyed. This is essentially the same issue that
we dealt with for <code>reverse_iterator</code> in DR <a href="lwg-defects.html#386" title="Reverse iterator's operator[] has impossible return type (Status: CD1)">386</a><sup><a href="https://cplusplus.github.io/LWG/issue386" title="Latest snapshot">(i)</a></sup>.
</p>

<p><i>[
2009-07-28 Reopened by Alisdair.  No longer solved by concepts.
]</i></p>


<p><i>[
2009-08-15 Howard adds:
]</i></p>


<blockquote><p>
I recommend closing this as  a duplicate of <a href="lwg-closed.html#1051" title="Specify subscript operation return types of reverse_iterator and move_iterator (Status: NAD)">1051</a><sup><a href="https://cplusplus.github.io/LWG/issue1051" title="Latest snapshot">(i)</a></sup> which addresses
this issue for both <code>move_iterator</code> and <code>reverse_iterator</code>.
</p></blockquote>

<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
Move to Ready. Note that if <a href="lwg-closed.html#1051" title="Specify subscript operation return types of reverse_iterator and move_iterator (Status: NAD)">1051</a><sup><a href="https://cplusplus.github.io/LWG/issue1051" title="Latest snapshot">(i)</a></sup> is reopened, it may yield a
better resolution, but <a href="lwg-closed.html#1051" title="Specify subscript operation return types of reverse_iterator and move_iterator (Status: NAD)">1051</a><sup><a href="https://cplusplus.github.io/LWG/issue1051" title="Latest snapshot">(i)</a></sup> is currently marked NAD.
</p></blockquote>



<p id="res-872"><b>Proposed resolution:</b></p>
<p>
In 24.5.4.2 <a href="https://wg21.link/move.iterator">[move.iterator]</a> and  [move.iter.op.index], change the declaration of
<code>move_iterator</code>'s <code>operator[]</code> to:
</p>

<blockquote><pre>
<del>reference</del> <ins><i>unspecified</i></ins> operator[](difference_type n) const;
</pre></blockquote>



<p><b>Rationale:</b></p>
<p><i>[
San Francisco:
]</i></p>


<blockquote><p>
NAD Editorial, see
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2777.pdf">N2777</a>.
</p></blockquote>




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