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<title>Issue 2523: std::promise synopsis shows two set_value_at_thread_exit()'s for no apparent reason</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="2523"><a href="lwg-defects.html#2523">2523</a>. <code>std::promise</code> synopsis shows two <code>set_value_at_thread_exit()</code>'s for no apparent reason</h3>
<p><b>Section:</b> 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a> <b>Status:</b> <a href="lwg-active.html#C++17">C++17</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2015-07-31 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#futures.promise">issues</a> in [futures.promise].</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>
In 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a>, the class synopsis shows
</p>
<blockquote><pre>
void set_value_at_thread_exit(const R&amp; r);
void set_value_at_thread_exit(<i>see below</i>);
</pre></blockquote>
<p>
There's no apparent reason for having <code>void set_value_at_thread_exit(const R&amp; r);</code>, especially as that 
signature isn't really present in the specializations (particularly <code>promise&lt;void&gt;</code>). Note that the similar 
<code>set_value</code> only has a <code>void set_value(<i>see below</i>);</code>
</p>
<p>
While we are here, 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a>/p1 says that the specializations "differ only in the argument type of the 
member function <code>set_value</code>", which missed <code>set_value_at_thread_exit</code>.
</p>

<p><i>[2015-10, Kona issue prioritization]</i></p>

<p>Priority 0, move to Ready</p>


<p id="res-2523"><b>Proposed resolution:</b></p>
<p>
This wording is relative to N4527.
</p>

<ol>
<li><p>Edit 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a>, class template <code>promise</code> synopsis, as indicated:</p>
<blockquote>
<pre>
namespace std {
  template &lt;class R&gt;
  class promise {
  public:
    [&hellip;]

    <i>// setting the result</i>
    void set_value(<i>see below</i>);
    void set_exception(exception_ptr p);
    
    <i>// setting the result with deferred notification</i>
    <del>void set_value_at_thread_exit(const R&amp; r);</del>
    void set_value_at_thread_exit(<i>see below</i>);
    void set_exception_at_thread_exit(exception_ptr p);
  };
}
</pre>
</blockquote>
</li>

<li><p>Edit 32.10.6 <a href="https://wg21.link/futures.promise">[futures.promise]</a>/1 as indicated:</p>
<blockquote>
<p>
-1- The implementation shall provide the template <code>promise</code> and two specializations, <code>promise&lt;R&amp;&gt;</code> and 
<code>promise&lt;void&gt;</code>. These differ only in the argument type of the member function<ins>s</ins> <code>set_value</code>
<ins>and <code>set_value_at_thread_exit</code></ins>, as set out in <del>its description</del><ins>their descriptions</ins>, below.
</p>
</blockquote>
</li>
</ol>





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