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<title>Issue 3067: recursive_directory_iterator::pop must invalidate</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++20">C++20</a> status.</em></p>
<h3 id="3067"><a href="lwg-defects.html#3067">3067</a>. <code>recursive_directory_iterator::pop</code> must invalidate</h3>
<p><b>Section:</b> 31.12.12.2 <a href="https://wg21.link/fs.rec.dir.itr.members">[fs.rec.dir.itr.members]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Casey Carter <b>Opened:</b> 2018-02-25 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#fs.rec.dir.itr.members">issues</a> in [fs.rec.dir.itr.members].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>recursive_directory_iterator::pop</code> is effectively a "supercharged" <code>operator++</code>: it
advances the iterator forward as many steps as are necessary to reach the next entry in the parent
directory. Just as is the case for <code>operator++</code>, <code>pop</code> must be allowed to invalidate
iterator copies to allow efficient implementation. The most efficient fix seems to be borrowing the
invalidation wording from 24.3.5.3 <a href="https://wg21.link/input.iterators">[input.iterators]</a> Table 87's specification for the required
<code>++r</code> expression for input iterators.
</p>

<p><i>[
2018-03-06 Moved to Tentatively Ready after 5 positive votes on c++std-lib.
]</i></p>


<p><i>[2018-06 Rapperswil: Adopted]</i></p>



<p id="res-3067"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4727">N4727</a>.
</p>

<ol>
<li><p>Change 31.12.12.2 <a href="https://wg21.link/fs.rec.dir.itr.members">[fs.rec.dir.itr.members]</a> as indicated:</p>
<blockquote>
<pre>
void pop();
void pop(error_code&amp; ec);
</pre>
<blockquote>
<p>
-26- <i>Effects</i>: If <code>depth() == 0</code>, set <code>*this</code> to
<code>recursive_directory_iterator()</code>. Otherwise, cease iteration of the directory currently being
iterated over, and continue iteration over the parent directory.
</p>
<p>
<ins>-?- <i>Postconditions</i>: Any copies of the previous value of <code>*this</code> are no longer
required either to be dereferenceable or to be in the domain of <code>==</code>.</ins>
</p>
<p>
-27- <i>Throws</i>: As specified in 31.12.5 <a href="https://wg21.link/fs.err.report">[fs.err.report]</a>.
</p>
</blockquote>
</blockquote>
</li>
</ol>





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