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<title>Issue 916: Redundant move-assignment operator of pair should be removed</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#NAD">NAD</a> status.</em></p>
<h3 id="916"><a href="lwg-closed.html#916">916</a>. Redundant move-assignment operator of <code>pair</code> should be removed</h3>
<p><b>Section:</b> 22.3 <a href="https://wg21.link/pairs">[pairs]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Daniel Kr&uuml;gler <b>Opened:</b> 2008-10-04 <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#pairs">issues</a> in [pairs].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>see also <a href="lwg-closed.html#917" title="Redundant move-assignment operator of tuple should be removed (Status: NAD)">917</a><sup><a href="https://cplusplus.github.io/LWG/issue917" title="Latest snapshot">(i)</a></sup>.</b></p>

<p>
The current WP provides the following assignment operators for <code>pair</code>
in 22.3 <a href="https://wg21.link/pairs">[pairs]</a>/1:
</p>

<ol>
<li>
<pre>
template&lt;class U , class V&gt;
requires HasAssign&lt;T1, const U&amp;&gt; &amp;&amp; HasAssign&lt;T2, const V&amp;&gt;
pair&amp; operator=(const pair&lt;U , V&gt;&amp; p);
</pre>
</li>
<li>
<pre>
requires MoveAssignable&lt;T1&gt; &amp;&amp; MoveAssignable&lt;T2&gt; pair&amp; operator=(pair&amp;&amp; p );
</pre>
</li>
<li>
<pre>
template&lt;class U , class V&gt;
requires HasAssign&lt;T1, RvalueOf&lt;U&gt;::type&gt; &amp;&amp; HasAssign&lt;T2, RvalueOf&lt;V&gt;::type&gt;
pair&amp; operator=(pair&lt;U , V&gt;&amp;&amp; p);
</pre>
</li>
</ol>

<p>
It seems that the functionality of (2) is completely covered by (3), therefore
(2) should be removed.
</p>

<p><i>[
Batavia (2009-05):
]</i></p>

<blockquote>
<p>
Bill believes the extra assignment operators are necessary for resolving
ambiguities, but that does not mean it needs to be part of the specification.
</p>
<p>
Move to Open.
We recommend this be looked at in the context of the ongoing work
related to the pair templates.
</p>
</blockquote>

<p><i>[
2009-07 Frankfurt:
]</i></p>


<blockquote><p>
Leave this open pending the removal of concepts from the WD.
</p></blockquote>

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


<blockquote><p>
Mark as NAD, see issue <a href="lwg-defects.html#801" title="tuple and pair trivial members (Status: Resolved)">801</a><sup><a href="https://cplusplus.github.io/LWG/issue801" title="Latest snapshot">(i)</a></sup>.
</p></blockquote>



<p id="res-916"><b>Proposed resolution:</b></p>
<ol style="list-style-type:upper-alpha">
<li>
<p>
In 22.3 <a href="https://wg21.link/pairs">[pairs]</a> p. 1, class <code>pair</code> and just before p. 13 remove the declaration:
</p>

<blockquote><pre>
requires MoveAssignable&lt;T1&gt; &amp;&amp; MoveAssignable&lt;T2&gt; pair&amp; operator=(pair&amp;&amp; p );
</pre></blockquote>
</li>

<li>
Remove p.13+p.14
</li>

</ol>





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