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<title>Issue 3719: Directory iterators should be usable with default sentinel</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++23">C++23</a> status.</em></p>
<h3 id="3719"><a href="lwg-defects.html#3719">3719</a>. Directory iterators should be usable with default sentinel</h3>
<p><b>Section:</b> 31.12.11.1 <a href="https://wg21.link/fs.class.directory.iterator.general">[fs.class.directory.iterator.general]</a>, 31.12.12.1 <a href="https://wg21.link/fs.class.rec.dir.itr.general">[fs.class.rec.dir.itr.general]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2022-06-17 <b>Last modified:</b> 2024-01-29</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
We added comparisons with <code>default_sentinel_t</code> to the stream and streambuf iterators, because their
past-the-end iterator is just a default-constructed iterator. We didn't do the same for filesystem directory
iterators, but they also use a default-constructed value as the sentinel.
<p/>
The proposed resolution addresses this oversight.
</p>

<p>
<strong>Previous resolution [SUPERSEDED]:</strong>
</p>
<blockquote class="note">
<p>
This wording is relative to <a href="https://wg21.link/N4910" title=" Working Draft, Standard for Programming Language C++">N4910</a>.
</p>

<ol>
<li><p>Modify 31.12.11.1 <a href="https://wg21.link/fs.class.directory.iterator.general">[fs.class.directory.iterator.general]</a>, class <code>directory_iterator</code> synopsis,
as indicated:</p>

<blockquote>
<pre>
namespace std::filesystem {
  class directory_iterator {
    [&hellip;]

    const directory_entry&amp; operator*() const;
    const directory_entry* operator-&gt;() const;
    directory_iterator&amp; operator++();
    directory_iterator&amp; increment(error_code&amp; ec);

    <ins>friend bool operator==(const directory_iterator&amp; lhs, default_sentinel_t) noexcept
    { return lhs == end(lhs); }</ins>

    <i>// other members as required by 24.3.5.3 <a href="https://wg21.link/input.iterators">[input.iterators]</a>, input iterators</i>
  };
}
</pre>
</blockquote>
</li>

<li><p>Modify 31.12.12.1 <a href="https://wg21.link/fs.class.rec.dir.itr.general">[fs.class.rec.dir.itr.general]</a>, class <code>recursive_directory_iterator</code> synopsis,
as indicated:</p>

<blockquote>
<pre>
namespace std::filesystem {
  class recursive_directory_iterator {
    [&hellip;]

    void pop();
    void pop(error_code&amp; ec);
    void disable_recursion_pending();

    <ins>friend bool operator==(const recursive_directory_iterator&amp; lhs, default_sentinel_t) noexcept
    { return lhs == end(lhs); }</ins>

    <i>// other members as required by 24.3.5.3 <a href="https://wg21.link/input.iterators">[input.iterators]</a>, input iterators</i>
  };
}
</pre>
</blockquote>
</li>

</ol>
</blockquote>

<p><i>[2022-07-06; Jonathan Wakely revises proposed resolution and adds
regex iterators as suggested on the reflector.]</i></p>



<p><i>[2022-07-11; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after six votes in favour during reflector poll.
</p>

<p><i>[2022-07-15; LWG telecon: move to Ready]</i></p>


<p><i>[2022-07-25 Approved at July 2022 virtual plenary. Status changed: Ready &rarr; WP.]</i></p>



<p id="res-3719"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4910" title=" Working Draft, Standard for Programming Language C++">N4910</a>.
</p>

<ol>
<li><p>Modify 31.12.11.1 <a href="https://wg21.link/fs.class.directory.iterator.general">[fs.class.directory.iterator.general]</a>, class <code>directory_iterator</code> synopsis,
as indicated:</p>

<blockquote>
<pre>
namespace std::filesystem {
  class directory_iterator {
    [&hellip;]

    const directory_entry&amp; operator*() const;
    const directory_entry* operator-&gt;() const;
    directory_iterator&amp; operator++();
    directory_iterator&amp; increment(error_code&amp; ec);

    <ins>bool operator==(default_sentinel_t) const noexcept</ins>
    <ins>{ return *this == directory_iterator(); }</ins>

    <i>// other members as required by 24.3.5.3 <a href="https://wg21.link/input.iterators">[input.iterators]</a>, input iterators</i>
  };
}
</pre>
</blockquote>
</li>

<li><p>Modify 31.12.12.1 <a href="https://wg21.link/fs.class.rec.dir.itr.general">[fs.class.rec.dir.itr.general]</a>, class <code>recursive_directory_iterator</code> synopsis,
as indicated:</p>

<blockquote>
<pre>
namespace std::filesystem {
  class recursive_directory_iterator {
    [&hellip;]

    void pop();
    void pop(error_code&amp; ec);
    void disable_recursion_pending();

    <ins>bool operator==(default_sentinel_t) const noexcept</ins>
    <ins>{ return *this == recursive_directory_iterator(); }</ins>

    <i>// other members as required by 24.3.5.3 <a href="https://wg21.link/input.iterators">[input.iterators]</a>, input iterators</i>
  };
}
</pre>
</blockquote>
</li>

<li><p>Modify 28.6.11.1.1 <a href="https://wg21.link/re.regiter.general">[re.regiter.general]</a>, <code>regex_iterator</code> synopsis, as indicated:</p>

<blockquote>
<pre>
namespace std {
  template&lt;class BidirectionalIterator,
            class charT = typename iterator_traits&lt;BidirectionalIterator&gt;::value_type,
            class traits = regex_traits&lt;charT&gt;&gt;
    class regex_iterator {
      [&hellip;]
      regex_iterator&amp; operator=(const regex_iterator&amp;);
      bool operator==(const regex_iterator&amp;) const;
      <ins>bool operator==(default_sentinel_t) const { return *this == regex_iterator(); }</ins>
      const value_type&amp; operator*() const;
      const value_type* operator-&gt;() const;
</pre>
</blockquote>
</li>

<li><p>Modify 28.6.11.2.1 <a href="https://wg21.link/re.tokiter.general">[re.tokiter.general]</a>, <code>regex_token_iterator</code> synopsis, as indicated:</p>

<blockquote>
<pre>
namespace std {
  template&lt;class BidirectionalIterator,
            class charT = typename iterator_traits&lt;BidirectionalIterator&gt;::value_type,
            class traits = regex_traits&lt;charT&gt;&gt;
    class regex_token_iterator {
      [&hellip;]
      regex_iterator&amp; operator=(const regex_token_iterator&amp;);
      bool operator==(const regex_token_iterator&amp;) const;
      <ins>bool operator==(default_sentinel_t) const { return *this == regex_token_iterator(); }</ins>
      const value_type&amp; operator*() const;
      const value_type* operator-&gt;() const;
</pre>
</blockquote>
</li>

</ol>





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