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<title>Issue 3764: reference_wrapper::operator() should propagate noexcept</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++23">C++23</a> status.</em></p>
<h3 id="3764"><a href="lwg-defects.html#3764">3764</a>. <code>reference_wrapper::operator()</code> should propagate <code>noexcept</code></h3>
<p><b>Section:</b> 22.10.6.5 <a href="https://wg21.link/refwrap.invoke">[refwrap.invoke]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Zhihao Yuan <b>Opened:</b> 2022-08-31 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#refwrap.invoke">issues</a> in [refwrap.invoke].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The following assertion does not hold, making
the type less capable than the function pointers.
</p>
<blockquote><pre>
void f() noexcept;

std::reference_wrapper fn = f;
static_assert(std::is_nothrow_invocable_v&lt;decltype(fn)&gt;);
</pre></blockquote>

<p><i>[2022-09-23; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after six votes in favour during reflector poll.
</p>
<p>
Already implemented in MSVC and libstdc++.
</p>

<p><i>[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3764"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4910" title=" Working Draft, Standard for Programming Language C++">N4910</a>.
</p>

<ol>

<li><p>Modify 22.10.6.1 <a href="https://wg21.link/refwrap.general">[refwrap.general]</a>, class template <code>reference_wrapper</code> synopsis, as indicated:</p>

<blockquote>
<pre>
<i>// 22.10.6.5 <a href="https://wg21.link/refwrap.invoke">[refwrap.invoke]</a>, invocation</i>
template&lt;class... ArgTypes&gt;
  constexpr invoke_result_t&lt;T&amp;, ArgTypes...&gt; operator()(ArgTypes&amp;&amp;...) const 
    <ins>noexcept(is_nothrow_invocable_v&lt;T&amp;, ArgTypes...&gt;)</ins>;
</pre>
</blockquote>
</li>

<li><p>Modify 22.10.6.5 <a href="https://wg21.link/refwrap.invoke">[refwrap.invoke]</a> as indicated:</p>

<blockquote>
<pre>
template&lt;class... ArgTypes&gt;
  constexpr invoke_result_t&lt;T&amp;, ArgTypes...&gt;
    operator()(ArgTypes&amp;&amp;... args) const <ins>noexcept(is_nothrow_invocable_v&lt;T&amp;, ArgTypes...&gt;)</ins>;
</pre>
<blockquote>
<p>
-1- <i>Mandates</i>: <code>T</code> is a complete type.
<p/>
-2- <i>Returns</i>: <code><i>INVOKE</i>(get(), std::forward&lt;ArgTypes&gt;(args)...)</code>. (22.10.4 <a href="https://wg21.link/func.require">[func.require]</a>)
</p>
</blockquote>
</blockquote>
</li>

</ol>





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