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<title>Issue 2641: [filesys.ts] [PDTS] directory_iterator, recursive_directory_iterator, move construct/assign should be noexcept</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#TS">TS</a> status.</em></p>
<h3 id="2641"><a href="lwg-defects.html#2641">2641</a>. [filesys.ts] [PDTS] <code>directory_iterator</code>, <code>recursive_directory_iterator</code>, move construct/assign should be <code>noexcept</code></h3>
<p><b>Section:</b> 13 [filesys.ts::class.directory_iterator], 14 [filesys.ts::class.rec.dir.itr] <b>Status:</b> <a href="lwg-active.html#TS">TS</a>
 <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2014-01-30 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#filesys.ts::class.directory_iterator">issues</a> in [filesys.ts::class.directory_iterator].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TS">TS</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses: filesys.ts</b></p>
<p>
<code>class directory_iterator</code> move construct/assign should be <code>noexcept</code>.<br/>
<code>class recursive_directory_iterator</code> move construct/assign should be <code>noexcept</code>.
</p>

<p><i>[Beman Dawes 2014-02-27]</i></p>


  <p/>Issues <a href="lwg-defects.html#2637" title="[filesys.ts] [PDTS] All functions with error_code arguments should be noexcept (Status: TS)">2637</a><sup><a href="https://cplusplus.github.io/LWG/issue2637" title="Latest snapshot">(i)</a></sup>,
  <a href="lwg-closed.html#2638" title="[filesys.ts] [PDTS] Make certain functions noexcept and drop error_code version (Status: NAD)">2638</a><sup><a href="https://cplusplus.github.io/LWG/issue2638" title="Latest snapshot">(i)</a></sup>,
  <a href="lwg-defects.html#2641" title="[filesys.ts] [PDTS] directory_iterator, recursive_directory_iterator, move construct/assign should be noexcept (Status: TS)">2641</a><sup><a href="https://cplusplus.github.io/LWG/issue2641" title="Latest snapshot">(i)</a></sup>,
  and <a href="lwg-defects.html#2649" title="[filesys.ts] [PDTS] path and directory_entry move ctors should not be noexcept (Status: TS)">2649</a><sup><a href="https://cplusplus.github.io/LWG/issue2649" title="Latest snapshot">(i)</a></sup> are concerned with signatures which should or should not
  be <code>noexcept</code>. I will provide unified proposed wording for these issues, possibly in a separate paper.
  <p><i>[Daniel Krügler 2014-02-28]</i></p>


<pre>directory_iterator begin(directory_iterator iter) noexcept;
directory_iterator end(const directory_iterator&amp;) noexcept;</pre>

<p/>are noexcept, but we have no guarantee that at least the
move-constructor is noexcept:

<pre>directory_iterator(const directory_iterator&amp;) = default;
directory_iterator(directory_iterator&amp;&amp;) = default;</pre>

<p/>This means that either the above noexcept specifications are not
warranted or that at least the move-constructor of <code>directory_iterator</code>
is required to be noexcept.

<p/>The same applies to <code>recursive_directory_iterator</code>.

<p><i>[21 May 2014 Beman Dawes provided proposed resolution wording.]</i></p>

  <p><i>[18 Jun 2014 "= default" removed per LWG discussion]</i></p>



<p id="res-2641"><b>Proposed resolution:</b></p>
<p>
  <i>Change 13 Class directory_iterator [class.directory_iterator]:</i></p>
  <blockquote>
    <pre>directory_iterator(const directory_iterator&amp; <ins>rhs</ins>) <del>= default</del>;
directory_iterator(directory_iterator&amp;&amp; <ins>rhs</ins>) <ins>noexcept</ins> <del>= default</del>;
...
directory_iterator&amp; operator=(const directory_iterator&amp; <ins>rhs</ins>) <del>= default</del>;
directory_iterator&amp; operator=(directory_iterator&amp;&amp; <ins>rhs</ins>) <ins>noexcept</ins> <del>= default</del>;</pre>
  </blockquote>

  <p/><i>To 13.1 directory_iterator members [directory_iterator.members] add:</i>
  <blockquote>
    <pre>directory_iterator(const directory_iterator&amp; rhs);
directory_iterator(directory_iterator&amp;&amp; rhs) noexcept;</pre>
    <blockquote>
      <p>
        <i>Effects:</i> Constructs an object of class <code>directory_iterator</code>.
      </p>
      <p>
        <i>Postconditions:</i> <code>*this</code> has the original value of <code>rhs</code>.
      </p>

    </blockquote>
    <pre>directory_iterator&amp; operator=(const directory_iterator&amp; rhs);
directory_iterator&amp; operator=(directory_iterator&amp;&amp; rhs) noexcept;</pre>
    <blockquote>
      <p>
        <i>Effects:</i>  
        If <code>*this</code> and <code>rhs</code> are the same object, the member has no effect.
      </p>
      <p>
        <i>Postconditions:</i> <code>*this</code> has the original value of <code>rhs</code>.
      </p>
      <p/><i>Returns:</i>
      <code>*this</code>.

    </blockquote>
  </blockquote>

  <p>
    <i>Change 14 Class recursive_directory_iterator [class.rec.dir.itr]:</i>
  </p>
  <blockquote>
    <pre>recursive_directory_iterator(const recursive_directory_iterator&amp; <ins>rhs</ins>) <del>= default</del>;
recursive_directory_iterator(recursive_directory_iterator&amp;&amp; <ins>rhs</ins>) <ins>noexcept</ins> <del>= default</del>;
...
recursive_directory_iterator&amp; operator=(const recursive_directory_iterator&amp; <ins>rhs</ins>) <del>= default</del>;
recursive_directory_iterator&amp; operator=(recursive_directory_iterator&amp;&amp; <ins>rhs</ins>) <ins>noexcept</ins> <del>= default</del>;</pre>
  </blockquote>
  <p/>
  <i>To 14.1 recursive_directory_iterator members [rec.dir.itr.members] add:</i>
  <blockquote>
    <pre>recursive_directory_iterator(const recursive_directory_iterator&amp; rhs);</pre>
    <blockquote>
      <p>
        <i>Effects:</i> Constructs an object of class <code>recursive_directory_iterator</code>.
      </p>
      <p>
        <i>Postconditions:</i> <code>this->options() == rhs.options() &amp;&amp; this->depth() ==
        rhs.depth() &amp;&amp; this->recursion_pending() ==
        rhs.recursion_pending()</code>.
      </p>
    </blockquote>

    <pre>recursive_directory_iterator(recursive_directory_iterator&amp;&amp; rhs) noexcept;</pre>
    <blockquote>
      <p>
        <i>Effects:</i> Constructs an object of class <code>recursive_directory_iterator</code>.
      </p>
      <p>
        <i>Postconditions:</i> <code>this->options()</code>, <code>this->depth()</code>, and
        <code>this->recursion_pending()</code> return the values that
        <code>rhs.options()</code>, <code>rhs.depth()</code>, and <code>rhs.recursion_pending()</code>,
        respectively, had before the function call.
      </p>
    </blockquote>

    <pre>recursive_directory_iterator&amp; operator=(const recursive_directory_iterator&amp; rhs);</pre>
    <blockquote>
      <p>
        <i>Effects:</i> 
        If <code>*this</code> and <code>rhs</code> are the same object, the member has no effect.
      </p>
      <p>
      <i>Postconditions:</i> <code>
        this->options() == rhs.options() &amp;&amp; this->depth() ==
        rhs.depth() &amp;&amp; this->recursion_pending() ==
        rhs.recursion_pending()
      </code>.
      </p>

      <p/><i>Returns:</i>
      <code>*this</code>.

    </blockquote>

    <pre>recursive_directory_iterator&amp; operator=(recursive_directory_iterator&amp;&amp; rhs) noexcept;</pre>
    <blockquote>
      <p>
        <i>Effects:</i> 
        If <code>*this</code> and <code>rhs</code> are the same object, the member has no effect.
      </p>
      <p>
        <i>Postconditions:</i>
        <code>this->options()</code>, <code>this->depth()</code>, and
        <code>this->recursion_pending()</code> return the values that
        <code>rhs.options()</code>, <code>rhs.depth()</code>, and <code>rhs.recursion_pending()</code>,
        respectively, had before the function call.
      </p>
      <p/><i>Returns:</i> <code>*this</code>.

    </blockquote>
  </blockquote>







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