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<title>Issue 2574: [fund.ts.v2] std::experimental::function::operator=(F&amp;&amp;) should be constrained</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#TS">TS</a> status.</em></p>
<h3 id="2574"><a href="lwg-defects.html#2574">2574</a>. [fund.ts.v2] <code>std::experimental::function::operator=(F&amp;&amp;)</code> should be constrained</h3>
<p><b>Section:</b> 4.2.1 <a href="https://cplusplus.github.io/fundamentals-ts/v2.html#func.wrap.func.con">[fund.ts.v2::func.wrap.func.con]</a> <b>Status:</b> <a href="lwg-active.html#TS">TS</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2015-12-05 <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#fund.ts.v2::func.wrap.func.con">issues</a> in [fund.ts.v2::func.wrap.func.con].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TS">TS</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses: fund.ts.v2</b></p>
<p>
LWG <a href="lwg-defects.html#2132" title="std::function ambiguity (Status: C++14)">2132</a><sup><a href="https://cplusplus.github.io/LWG/issue2132" title="Latest snapshot">(i)</a></sup> constrained <code>std::function</code>'s constructor and assignment operator from callable objects for C++14. 
The constructors of <code>std::experimental::function</code> isn't separately specified in the fundamentals TS and so inherited the 
constraints from C++14, but the assignment operator is separately specified and presumably needs to be constrained.
</p>

<p><i>[2016-02, Issues Telecon]</i></p>

<p>
P0; move to Tentatively Ready.
</p>


<p id="res-2574"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4562.html">N4562</a>.
</p>

<ol>
<li><p>Insert a paragraph after 4.2.1 <a href="https://cplusplus.github.io/fundamentals-ts/v2.html#func.wrap.func.con">[fund.ts.v2::func.wrap.func.con]</a>/15 as indicated:</p>

<blockquote>
<pre>
template&lt;class F&gt; function&amp; operator=(F&amp;&amp; f);
</pre>
<blockquote>
<p>
-14- <i>Effects</i>: <code>function(allocator_arg, <i>ALLOCATOR_OF</i>(*this), std::forward&lt;F&gt;(f)).swap(*this);</code>
<p/>
-15- <i>Returns</i>: <code>*this</code>. 
<p/>
<ins>-?- <i>Remarks</i>: This assignment operator shall not participate in overload resolution unless 
<code>declval&lt;decay_t&lt;F&gt;&amp;&gt;()</code> is Callable (C++14 &sect;20.9.11.2) for argument types 
<code>ArgTypes...</code> and return type <code>R</code>.</ins>
</p>
</blockquote>
</blockquote>

</li>
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