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<title>Issue 3039: Unnecessary decay in thread and packaged_task</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++20">C++20</a> status.</em></p>
<h3 id="3039"><a href="lwg-defects.html#3039">3039</a>. Unnecessary <code>decay</code> in <code>thread</code> and <code>packaged_task</code></h3>
<p><b>Section:</b> 32.4.3.3 <a href="https://wg21.link/thread.thread.constr">[thread.thread.constr]</a>, 32.10.10.2 <a href="https://wg21.link/futures.task.members">[futures.task.members]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Stephan T. Lavavej  <b>Opened:</b> 2017-11-17 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View other</b> <a href="lwg-index-open.html#thread.thread.constr">active issues</a> in [thread.thread.constr].</p>
<p><b>View all other</b> <a href="lwg-index.html#thread.thread.constr">issues</a> in [thread.thread.constr].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Following <a href="https://wg21.link/p0777r1">P0777R1</a> "Treating Unnecessary decay", more occurrences can be fixed. 
When constraints are checking for the same type as <code>thread</code> or a specialization of <code>packaged_task</code>, 
decaying functions to function pointers and arrays to object pointers can't affect the result.
</p>

<p><i>[28-Nov-2017 Moved to Tentatively Ready after five positive votes on the ML.]</i></p>

<p><i>[2018-3-17 Adopted in Jacksonville]</i></p>



<p id="res-3039"><b>Proposed resolution:</b></p>
<p>
Wording relative to <a href="https://wg21.link/n4700">N4700</a>.
</p>

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<li>
<p>
Edit 32.4.3.3 <a href="https://wg21.link/thread.thread.constr">[thread.thread.constr]</a> as indicated:
</p>
<blockquote>
<pre>
template &lt;class F, class... Args&gt; explicit thread(F&amp;&amp; f, Args&amp;&amp;... args);
</pre>
<blockquote>
<p>
-3- <i>Requires:</i> [&hellip;]
<p/>
-4- <i>Remarks:</i> This constructor shall not participate in overload resolution if 
<code><del>decay_t</del><ins>remove_cvref_t</ins>&lt;F&gt;</code> is the same type as <code>std::thread</code>.
</p>
</blockquote>
</blockquote>
</li>

<li>
<p>
Edit 32.10.10.2 <a href="https://wg21.link/futures.task.members">[futures.task.members]</a> as indicated:
</p>
<blockquote>
<pre>
template &lt;class F&gt;
  packaged_task(F&amp;&amp; f);
</pre>
<blockquote>
<p>
-2- <i>Requires:</i> [&hellip;]
<p/>
-3- <i>Remarks:</i> This constructor shall not participate in overload resolution if 
<code><del>decay_t</del><ins>remove_cvref_t</ins>&lt;F&gt;</code> is the same type as <code>packaged_task&lt;R(ArgTypes...)&gt;</code>.
</p>
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