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<title>Issue 3423: std::any_cast should never return a cv-qualified type</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#New">New</a> status.</em></p>
<h3 id="3423"><a href="lwg-active.html#3423">3423</a>. <code>std::any_cast</code> should never return a <i>cv</i>-qualified type</h3>
<p><b>Section:</b> 22.7.5 <a href="https://wg21.link/any.nonmembers">[any.nonmembers]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Casey Carter <b>Opened:</b> 2020-04-02 <b>Last modified:</b> 2020-09-06</p>
<p><b>Priority: </b>3
</p>
<p><b>View all other</b> <a href="lwg-index.html#any.nonmembers">issues</a> in [any.nonmembers].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The return type of the non-pointer overloads of <code>std::any_cast&lt;T&gt;</code> is <code>T</code>. This is silly 
when <code>T</code> is <i>cv</i>-qualified (and, since merging <a href="https://wg21.link/p1152">P1152</a> 
"Deprecating volatile" into the working draft, deprecated when <code>T</code> is <code>volatile</code>-qualified). 
We should strip <i>cv</i>-qualifiers to determine the type returned.
</p>

<p><i>[2020-04-18 Issue Prioritization]</i></p>

<p>Priority to 3 after reflector discussion.</p>


<p id="res-3423"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4861">N4861</a>.
</p>

<ol>
<li><p>Modify 22.7.2 <a href="https://wg21.link/any.synop">[any.synop]</a> as indicated:</p>

<blockquote>
<pre>
[&hellip;]
template&lt;class T&gt;
  <ins>remove_cv_t&lt;</ins>T<ins>&gt;</ins> any_cast(const any&amp; operand);
template&lt;class T&gt;
  <ins>remove_cv_t&lt;</ins>T<ins>&gt;</ins> any_cast(any&amp; operand);
template&lt;class T&gt;
  <ins>remove_cv_t&lt;</ins>T<ins>&gt;</ins> any_cast(any&amp;&amp; operand);
[&hellip;]
</pre>
</blockquote>
</li>

<li><p>Modify 22.7.5 <a href="https://wg21.link/any.nonmembers">[any.nonmembers]</a> as indicated:</p>

<blockquote>
<pre>
template&lt;class T&gt;
  <ins>remove_cv_t&lt;</ins>T<ins>&gt;</ins> any_cast(const any&amp; operand);
template&lt;class T&gt;
  <ins>remove_cv_t&lt;</ins>T<ins>&gt;</ins> any_cast(any&amp; operand);
template&lt;class T&gt;
  <ins>remove_cv_t&lt;</ins>T<ins>&gt;</ins> any_cast(any&amp;&amp; operand);
</pre>
<blockquote>
<p>
-4- Let <ins><code>R</code> be the type <code>remove_cv_t&lt;T&gt;</code>, and</ins> <code>U</code> 
be the type <code>remove_cvref_t&lt;T&gt;</code>.
<p/>
-5- <i>Mandates:</i> For the first overload, <code>is_constructible_v&lt;<del>T</del><ins>R</ins>, const U&amp;&gt;</code> is <code>true</code>. 
For the second overload, <code>is_constructible_v&lt;<del>T</del><ins>R</ins>, U&amp;&gt;</code> is <code>true</code>. For the third overload, 
<code>is_constructible_v&lt;<del>T</del><ins>R</ins>, U&gt;</code> is <code>true</code>.
<p/>
-6- <i>Returns:</i> For the first and second overload, <code>static_cast&lt;<del>T</del><ins>R</ins>&gt;(*any_cast&lt;U&gt;(&amp;operand))</code>. 
For the third overload, <code>static_cast&lt;<del>T</del><ins>R</ins>&gt;(std::move(*any_cast&lt;U&gt;(&amp;operand)))</code>.
<p/>
-7- <i>Throws:</i> <code>bad_any_cast</code> if <code>operand.type() != typeid(remove_reference_t&lt;T&gt;)</code>.
</p>
</blockquote>
</blockquote>
</li>
</ol>




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