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<title>Issue 1088: std::promise should provide non-member swap overload</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#Resolved">Resolved</a> status.</em></p>
<h3 id="1088"><a href="lwg-defects.html#1088">1088</a>. <code>std::promise</code> should provide non-member <code>swap</code> overload</h3>
<p><b>Section:</b> 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#futures.promise">issues</a> in [futures.promise].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses UK 342 [CD1]</b></p>

<p>
<code>std::promise</code> is missing a non-member overload of <code>swap</code>. This is
inconsistent with other types that provide a <code>swap</code> member function.
</p>

<p>
Add a non-member overload <code>void swap(promise&amp;&amp; x,promise&amp;&amp; y){ x.swap(y); }</code>
</p>

<p><i>[
Summit:
]</i></p>

<blockquote><p>
Create an issue. Move to review, attention: Howard. Detlef will also look into it.
</p></blockquote>

<p><i>[
Post Summit Daniel provided wording.
]</i></p>


<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
<del>NAD Editorial</del><ins>Resolved</ins>.  Addressed by
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2997.htm">N2997</a>.
</p></blockquote>



<p id="res-1088"><b>Proposed resolution:</b></p>
<ol>
<li>
<p>
In 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a>, before p.1, immediately after class template
promise add:
</p>
<blockquote><pre>
<ins>
template &lt;class R&gt;
void swap(promise&lt;R&gt;&amp; x, promise&lt;R&gt;&amp; y);
</ins>
</pre></blockquote>
</li>
<li>
<p>
Change 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a>/10 as indicated (to fix a circular definition):
</p>
<blockquote>
<p>
-10- <i>Effects:</i> <del>swap(*this, other)</del><ins>Swaps the associated state
of <code>*this</code> and <code>other</code></ins>
</p>
<p>
<ins><i>Throws:</i> Nothing.</ins>
</p>
</blockquote>
</li>
<li>
<p>
After the last paragraph in 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a> add the following
prototype description:
</p>
<blockquote><pre>
<ins>
template &lt;class R&gt;
void swap(promise&lt;R&gt;&amp; x, promise&lt;R&gt;&amp; y);
</ins></pre>
<blockquote>
<p>
<ins><i>Effects:</i> <code>x.swap(y)</code></ins>
</p>
<p>
<ins><i>Throws:</i> Nothing.</ins>
</p>
</blockquote>
</blockquote>
</li>

</ol>






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