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<title>Issue 2807: std::invoke should use std::is_nothrow_callable</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++17">C++17</a> status.</em></p>
<h3 id="2807"><a href="lwg-defects.html#2807">2807</a>. <code>std::invoke</code> should use <code>std::is_nothrow_callable</code></h3>
<p><b>Section:</b> 22.10.5 <a href="https://wg21.link/func.invoke">[func.invoke]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Great Britain <b>Opened:</b> 2016-11-09 <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#func.invoke">issues</a> in [func.invoke].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++17">C++17</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<b>Addresses GB 53</b>
</p>
<p>
<code>std::invoke</code> can be made trivially <code>noexcept</code> 
using the new <code>std::is_nothrow_callable</code> trait:
</p>
<p>
Proposed change:
<p/>
Add the exception specifier <code>noexcept(is_nothrow_callable_v&lt;F&amp;&amp;(Args&amp;&amp;...)&gt;)</code> 
to <code>std::invoke</code>.
</p>

<p><i>[Issues Telecon 16-Dec-2016]</i></p>

<p>Priority 3</p>

<p><i>[2017-02-28, Daniel comments and provides wording]</i></p>

<p>
The following wording <em>assumes</em> that D0604R0 would be accepted, therefore uses <code>is_nothrow_invocable_v</code>
instead of the suggested current trait <code>is_nothrow_callable_v</code>
</p>

<p><i>[Kona 2017-03-01]</i></p>

<p>Accepted as Immediate to resolve NB comment.</p>


<p id="res-2807"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4640">N4640</a>.
</p>

<ol>
<li><p>Change 22.10.2 <a href="https://wg21.link/functional.syn">[functional.syn]</a>, header <code>&lt;functional&gt;</code> synopsis, as indicated:</p>

<blockquote><pre>
<i>// 20.14.4, invoke</i>
template &lt;class F, class... Args&gt;
  <ins>invoke_result_t&lt;F, Args...&gt;</ins><del>result_of_t&lt;F&amp;&amp;(Args&amp;&amp;...)&gt;</del> invoke(F&amp;&amp; f, Args&amp;&amp;... args) <ins>noexcept(is_nothrow_invocable_v&lt;F, Args...&gt;)</ins>;
</pre></blockquote>
</li>

<li><p>Change 22.10.5 <a href="https://wg21.link/func.invoke">[func.invoke]</a> as indicated:</p>

<blockquote><pre>
template &lt;class F, class... Args&gt;
  <ins>invoke_result_t&lt;F, Args...&gt;</ins><del>result_of_t&lt;F&amp;&amp;(Args&amp;&amp;...)&gt;</del> invoke(F&amp;&amp; f, Args&amp;&amp;... args) <ins>noexcept(is_nothrow_invocable_v&lt;F, Args...&gt;)</ins>;</pre></blockquote>
</li>

</ol>





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