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<title>Issue 2719: permissions function should not be noexcept due to narrow contract</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++17">C++17</a> status.</em></p>
<h3 id="2719"><a href="lwg-defects.html#2719">2719</a>. <code>permissions</code> function should not be <code>noexcept</code> due to narrow contract</h3>
<p><b>Section:</b> 31.12.13.27 <a href="https://wg21.link/fs.op.permissions">[fs.op.permissions]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Eric Fiselier <b>Opened:</b> 2016-05-28 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#fs.op.permissions">issues</a> in [fs.op.permissions].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++17">C++17</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Currently the signatures for <code>permissions</code> are:
</p>
<blockquote>
<pre>
void permissions(const path&amp; p, perms prms);
void permissions(const path&amp; p, perms prms, error_code&amp; ec) noexcept;
</pre>
</blockquote>
<p>
However both overloads have a narrow contract since due to the requires clause:
</p>
<blockquote>
<p>
<i>Requires:</i> <code>!((prms &amp; perms::add_perms) != perms::none
 &amp;&amp; (prms &amp; perms::remove_perms) != perms::none)</code>.
</p>
</blockquote>
<p>
For this reason I believe the second overload of <code>permissions</code> should not be marked <code>noexcept</code>.
</p>

<p><i>[2016-06 Oulu]</i></p>

<p>Moved to P0/Ready during issues prioritization.</p>
<p>Friday: status to Immediate</p>


<p id="res-2719"><b>Proposed resolution:</b></p>
<p>This wording is relative to N4582.</p>
<ol>
<li><p>Change 31.12.4 <a href="https://wg21.link/fs.filesystem.syn">[fs.filesystem.syn]</a> as indicated:</p>

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

  void permissions(const path&amp; p, perms prms);
  void permissions(const path&amp; p, perms prms, error_code&amp; ec) <del>noexcept</del>;

  [&hellip;]
}
</pre>
</blockquote>
</li>

<li><p>Change 31.12.13.27 <a href="https://wg21.link/fs.op.permissions">[fs.op.permissions]</a> as indicated:</p>

<blockquote>
<pre>
void permissions(const path&amp; p, perms prms);
void permissions(const path&amp; p, perms prms, error_code&amp; ec) <del>noexcept</del>;
</pre>
<blockquote>
<p>
-1- <i>Requires:</i> <code>!((prms &amp; perms::add_perms) != perms::none &amp;&amp; (prms &amp; perms::remove_perms)
!= perms::none)</code>.
</p>
</blockquote>
</blockquote>
</li>
</ol>





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