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<title>Issue 3498: Inconsistent noexcept-specifiers 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="3498"><a href="lwg-defects.html#3498">3498</a>. Inconsistent <code>noexcept</code>-specifiers for <code>basic_syncbuf</code></h3>
<p><b>Section:</b> 31.11.2.1 <a href="https://wg21.link/syncstream.syncbuf.overview">[syncstream.syncbuf.overview]</a>, 31.11.2.3 <a href="https://wg21.link/syncstream.syncbuf.assign">[syncstream.syncbuf.assign]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2020-11-10 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#syncstream.syncbuf.overview">issues</a> in [syncstream.syncbuf.overview].</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>
The synopsis in 31.11.2.1 <a href="https://wg21.link/syncstream.syncbuf.overview">[syncstream.syncbuf.overview]</a> shows the move assignment operator and
<code>swap</code> member as potentially throwing. The detailed descriptions in
31.11.2.3 <a href="https://wg21.link/syncstream.syncbuf.assign">[syncstream.syncbuf.assign]</a> are <code>noexcept</code>.
<p/>
Daniel:
<p/>
This mismatch is already present in the originally accepted paper
<a href="https://wg21.link/p0053r7">P0053R7</a>, so this is nothing that could be resolved editorially.
</p>

<p><i>[2020-11-21; Reflector prioritization]</i></p>

<p>
Set priority to 3 during reflector discussions.
</p>

<p><i>[2021-05-22 Tim adds PR]</i></p>

<p>The move assignment is specified to call <code>emit()</code> which can throw,
and there's nothing in the wording providing for catching/ignoring the exception,
so it can't be <code>noexcept</code>. The <code>swap</code> needs
to call <code>basic_streambuf::swap</code>, which isn't <code>noexcept</code>,
so it shouldn't be <code>noexcept</code> either.</p>

<p><i>[2021-06-23; Reflector poll]</i></p>

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

<p><i>[2021-10-14 Approved at October 2021 virtual plenary. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3498"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4885">N4885</a>.
</p>

<ol>
<li><p>Modify 31.11.2.3 <a href="https://wg21.link/syncstream.syncbuf.assign">[syncstream.syncbuf.assign]</a> as indicated:</p>

<blockquote>
<pre>
basic_syncbuf&amp; operator=(basic_syncbuf&amp;&amp; rhs) <del>noexcept</del>;
</pre>
<blockquote>
<p>
-1- <i>Effects</i>: [&hellip;]
<p/>
-2- <i>Postconditions</i>: [&hellip;]
<p/>
-3- <i>Returns</i>: [&hellip;]
<p/>
-4- <i>Remarks</i>: [&hellip;]
</p>
</blockquote>
<pre>
void swap(basic_syncbuf&amp; other) <del>noexcept</del>;
</pre>
<blockquote>
<p>
-5- <i>Preconditions</i>: [&hellip;]
<p/>
-6- <i>Effects</i>: [&hellip;]
</p>
</blockquote>
</blockquote>
</li>
</ol>





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