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<title>Issue 3041: Unnecessary decay in reference_wrapper</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++20">C++20</a> status.</em></p>
<h3 id="3041"><a href="lwg-defects.html#3041">3041</a>. Unnecessary <code>decay</code> in <code>reference_wrapper</code></h3>
<p><b>Section:</b> 22.10.6.2 <a href="https://wg21.link/refwrap.const">[refwrap.const]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Agust&iacute;n K-ballo Berg&eacute; <b>Opened:</b> 2017-12-04 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#refwrap.const">issues</a> in [refwrap.const].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Another occurrence of unnecessary decay (<a href="https://wg21.link/p0777">P0777</a>) was introduced by the
resolution of LWG <a href="lwg-defects.html#2993" title="reference_wrapper&lt;T&gt; conversion from T&amp;&amp; (Status: C++20)">2993</a><sup><a href="https://cplusplus.github.io/LWG/issue2993" title="Latest snapshot">(i)</a></sup>. A decayed function/array type will never be the same type as 
<code>reference_wrapper</code>.
</p>

<p><i>[
2018-01-09 Moved to Tentatively Ready after 9 positive votes on c++std-lib.
]</i></p>

<p><i>[2018-3-17 Adopted in Jacksonville]</i></p>



<p id="res-3041"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4713">N4713</a>.</p>

<ol>
<li><p>Change 22.10.6.2 <a href="https://wg21.link/refwrap.const">[refwrap.const]</a> as indicated:</p>

<blockquote>
<pre>template&lt;class U&gt;
reference_wrapper(U&amp;&amp; u) noexcept(<i>see below</i>);</pre>
<blockquote>
<p>
-1- <i>Remarks:</i> Let <code><i>FUN</i></code> denote the exposition-only functions
</p>
<pre>
void FUN(T&amp;) noexcept;
void FUN(T&amp;&amp;) = delete;
</pre>
<p>
This constructor shall not participate in overload resolution unless the expression <code><i>FUN</i>(declval&lt;U&gt;())</code>
is well-formed and <code>is_same_v&lt;<del>decay_t</del><ins>remove_cvref_t</ins>&lt;U&gt;, reference_wrapper&gt;</code> is 
<code>false</code>. The expression inside <code>noexcept</code> is equivalent to <code>noexcept(<i>FUN</i>(declval&lt;U&gt;()))</code>.
</p>
</blockquote>
</blockquote>
</li>

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