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<title>Issue 3616: LWG 3498 seems to miss the non-member swap for basic_syncbuf</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="3616"><a href="lwg-defects.html#3616">3616</a>. LWG 3498 seems to miss the non-member <code>swap</code> for <code>basic_syncbuf</code></h3>
<p><b>Section:</b> 31.11.2.6 <a href="https://wg21.link/syncstream.syncbuf.special">[syncstream.syncbuf.special]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> S. B. Tam <b>Opened:</b> 2021-10-07 <b>Last modified:</b> 2023-11-22</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>
LWG <a href="lwg-defects.html#3498" title="Inconsistent noexcept-specifiers for basic_syncbuf (Status: C++23)">3498</a><sup><a href="https://cplusplus.github.io/LWG/issue3498" title="Latest snapshot">(i)</a></sup> fixes the inconsistent <code>noexcept</code>-specifiers for member functions of <code>basic_syncbuf</code>, 
but the proposed resolution in LWG <a href="lwg-defects.html#3498" title="Inconsistent noexcept-specifiers for basic_syncbuf (Status: C++23)">3498</a><sup><a href="https://cplusplus.github.io/LWG/issue3498" title="Latest snapshot">(i)</a></sup> seems to miss the non-member <code>swap</code>, which also has 
inconsistent <code>noexcept</code>-specifier: 31.11.2.6 <a href="https://wg21.link/syncstream.syncbuf.special">[syncstream.syncbuf.special]</a> says it's <code>noexcept</code>, 
while 31.11.1 <a href="https://wg21.link/syncstream.syn">[syncstream.syn]</a> says it's not.
<p/>
Since the non-member <code>swap</code> and the member <code>swap</code> have equivalent effect, and LWG 3498 removes 
<code>noexcept</code> from the latter, I think it's pretty clear that the former should not be <code>noexcept</code>.
</p>

<p><i>[2021-10-14; Reflector poll]</i></p>

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

<p><i>[2022-02-10 Approved at February 2022 virtual plenary. Status changed: Tentatively Ready &rarr; WP.]</i></p>


<p><i>[2022-02-10; Jens comments]</i></p>

<p>
The desired fix was applied editorially while applying
<p/>
<a href="https://wg21.link/P2450" title=" C++ Standard Library Issues to be moved in Virtual Plenary, Oct. 2021">P2450</a> C++ Standard Library Issues to be moved in Virtual Plenary, Oct. 2021
</p>


<p id="res-3616"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4892">N4892</a>.
</p>

<ol>
<li><p>Modify 31.11.2.6 <a href="https://wg21.link/syncstream.syncbuf.special">[syncstream.syncbuf.special]</a> as indicated:</p>

<blockquote>
<pre>
template&lt;class charT, class traits, class Allocator&gt;
  void swap(basic_syncbuf&lt;charT, traits, Allocator&gt;&amp; a,
            basic_syncbuf&lt;charT, traits, Allocator&gt;&amp; b) <del>noexcept</del>;
</pre>
<blockquote>
<p>
-1- <i>Effects:</i> Equivalent to <code>a.swap(b)</code>.
</p>
</blockquote>
</blockquote>
</li>
</ol>




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