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<title>Issue 2595: reverse_iterator::operator[]'s return type revisited</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#New">New</a> status.</em></p>
<h3 id="2595"><a href="lwg-active.html#2595">2595</a>. <code>reverse_iterator::operator[]</code>'s return type revisited</h3>
<p><b>Section:</b> 24.5.1.2 <a href="https://wg21.link/reverse.iterator">[reverse.iterator]</a>, 24.5.1.6 <a href="https://wg21.link/reverse.iter.elem">[reverse.iter.elem]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Robert Haberlach <b>Opened:</b> 2016-02-28 <b>Last modified:</b> 2021-06-06</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#reverse.iterator">issues</a> in [reverse.iterator].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Issue <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> changed the return type of <code>reverse_iterator::operator[]</code> to unspecified. However,
as of N3066, the return type of a random access iterator's <code>operator[]</code> shall be convertible to <code>reference</code>;
thus the return type of <code>reverse_iterator::operator[]</code> should be <code>reference</code> (and it is in all common
implementations).
<p/>
Suggested resolution: Adjust 24.5.1.2 <a href="https://wg21.link/reverse.iterator">[reverse.iterator]</a>'s synopsis and 24.5.1.6 <a href="https://wg21.link/reverse.iter.elem">[reverse.iter.elem]</a> to
use <code>reference</code> instead of <code><i>unspecified</i></code>.
</p>

<p><i>[2021-06-06 Tim syncs wording to current working draft]</i></p>



<p id="res-2595"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4885" title=" Working Draft, Standard for Programming Language C++">N4885</a>.
</p>

<ol>
<li><p>Edit 24.5.1.2 <a href="https://wg21.link/reverse.iterator">[reverse.iterator]</a>, class template <code></code> synopsis, as indicated:</p>

<blockquote><pre>
namespace std {
  template &lt;class Iterator&gt;
  class reverse_iterator {
  public:
    [&hellip;]
    using reference         = iter_reference_t&lt;Iterator&gt;;
    [&hellip;]
    constexpr <ins>reference</ins><del><i>unspecified</i></del> operator[](difference_type n) const;
    [&hellip;]
  };
}
</pre></blockquote>

</li>

<li><p>Change 24.5.1.6 <a href="https://wg21.link/reverse.iter.elem">[reverse.iter.elem]</a> before p3 as indicated:</p>

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





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