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<title>Issue 3608: convertible_to and temporary-bound references</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="3608"><a href="lwg-active.html#3608">3608</a>. <code>convertible_to</code> and temporary-bound references</h3>
<p><b>Section:</b> 18.4.4 <a href="https://wg21.link/concept.convertible">[concept.convertible]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2021-09-28 <b>Last modified:</b> 2021-10-23</p>
<p><b>Priority: </b>3
</p>
<p><b>View other</b> <a href="lwg-index-open.html#concept.convertible">active issues</a> in [concept.convertible].</p>
<p><b>View all other</b> <a href="lwg-index.html#concept.convertible">issues</a> in [concept.convertible].</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 semantic requirements of <code>convertible_to</code> express implicit
conversion by means of a function:
</p>
<blockquote><pre>
To test(FromR (&amp;f)()) {
  return f();
}
</pre></blockquote>
<p>
and it requires that <code>static_cast&lt;To&gt;(f())</code> be equal to <code>test(f)</code> for some
equality-preserving function <code>f</code>. However, when <code>To</code> is a reference type
but <code>FromR</code> is such that the conversion binds the reference to a temporary, the 
<code>static_cast</code> is valid but <code>test(f)</code> would produce a dangling reference.
<p/>
We should rephrase this requirement to just perform the implicit conversion in words. Using a 
function handles the convert-<code>void</code>-to-<code>void</code> case, but the semantic requirements 
wording already excluded that case anyway.
</p>

<p><i>[2021-10-14; Reflector poll]</i></p>

<p>
Set priority to 3 after reflector poll.
</p>


<p id="res-3608"><b>Proposed resolution:</b></p>





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