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<title>Issue 3400: Does is_nothrow_convertible consider destruction of the destination 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="3400"><a href="lwg-active.html#3400">3400</a>. Does <code>is_nothrow_convertible</code> consider destruction of the destination type?</h3>
<p><b>Section:</b> 21.3.8 <a href="https://wg21.link/meta.rel">[meta.rel]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Jiang An <b>Opened:</b> 2020-02-10 <b>Last modified:</b> 2023-12-22</p>
<p><b>Priority: </b>3
</p>
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<p><b>Discussion:</b></p>
<p>
This issue was submitted after a previous <a href="https://github.com/cplusplus/draft/issues/3576">editorial 
change request</a> had been rejected by the project editors.
<p/>
I find that all known implementations (at least 
<a href="https://github.com/microsoft/STL/blob/master/stl/inc/type_traits#L1658">msvcstl</a>, 
<a href="https://github.com/llvm-mirror/libcxx/blob/master/include/type_traits#L1506">libc++</a>, 
<a href="https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/std/type_traits#L1458">libstdc++</a> and the sample in <a href="https://wg21.link/p0758r1#Appendix">P0758R1</a>) of <code>std::is_nothrow_convertible</code>
may be not clear enough to indicate that whether destruction of the destination type is considered (or not).
<p/>
For example, given a type <code>Weird</code> defined as
</p>
<blockquote><pre>
struct Weird 
{
  Weird(int) noexcept {}
  ~Weird() noexcept(false) {}
};
</pre></blockquote>
<p>
Then <code>std::is_nothrow_convertible_v&lt;int, Weird&gt;</code> is <code>false</code> in every known implementation. 
However, it seems that the conversion itself is <code>noexcept</code>.
</p>

<p><i>[2020-02-22, Daniel comments]</i></p>

<p>
This seems to be quite related to the existing issue LWG <a href="lwg-active.html#2116" title="is_nothrow_constructible and destructors (Status: Open)">2116</a><sup><a href="https://cplusplus.github.io/LWG/issue2116" title="Latest snapshot">(i)</a></sup>.
</p>

<p><i>[2020-03-11 Issue Prioritization]</i></p>

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

<p><i>[2023-12-22; Daniel comments]</i></p>

<p>
This issue should be resolved by LWG <a href="lwg-active.html#4028" title="std::is_(nothrow_)convertible should be reworded to avoid dependence on the return statement (Status: New)">4028</a><sup><a href="https://cplusplus.github.io/LWG/issue4028" title="Latest snapshot">(i)</a></sup>.
</p>


<p id="res-3400"><b>Proposed resolution:</b></p>




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