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<title>Issue 4310: Is "the completion of the invocation of the constructor" considered as an expression?</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="4310"><a href="lwg-active.html#4310">4310</a>. Is "the completion of the invocation of the constructor" considered as an expression?</h3>
<p><b>Section:</b> 32.4.3.3 <a href="https://wg21.link/thread.thread.constr">[thread.thread.constr]</a>, 32.4.3.6 <a href="https://wg21.link/thread.thread.member">[thread.thread.member]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> jim x <b>Opened:</b> 2025-08-06 <b>Last modified:</b> 2025-08-09</p>
<p><b>Priority: </b>Not Prioritized
</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#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
32.4.3.3 <a href="https://wg21.link/thread.thread.constr">[thread.thread.constr]</a> p6 says
</p>
<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
<p>
The completion of the invocation of the constructor synchronizes with the beginning of the invocation of the copy of <code class='backtick'>f</code>.
</p>
</blockquote>
<p>
The intended meaning is that "The completion of the invocation of the constructor" happens-before 
"the beginning of the invocation of the copy of <code class='backtick'>f</code>.", so we can infer other happen-before relationships 
based on this point. 
<p/>
However, according to the definition of "happens-before" (6.10.2.2 <a href="https://wg21.link/intro.races">[intro.races]</a> p7),
</p>
<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
<p>
An evaluation <i>A</i> <i>happens before</i> an evaluation <i>B</i> (or, equivalently, <i>B</i> 
happens after <i>A</i>) if either
</p>
<ol style="list-style-type: none">
<li><p>(7.1) &mdash; [&hellip;]</p></li>
<li><p>(7.2) &mdash; <i>A</i> synchronizes with <i>B</i>, or</p></li>
</ol>
</blockquote>
<p>
That means <i>A</i> and <i>B</i> are first required to be expressions because the evaluation is 
in terms of expressions. 
<p/>
However, "The completion of the invocation of the constructor" and "the beginning of the invocation 
of the copy of <code class='backtick'>f</code>" are not expressions. 
<p/>
The similar issue is 32.4.3.6 <a href="https://wg21.link/thread.thread.member">[thread.thread.member]</a> p4
</p>
<blockquote style="border-left: 3px solid #ccc;padding-left: 15px;">
<p>
The completion of the thread represented by <code class='backtick'>*this</code> synchronizes with (6.10.2 <a href="https://wg21.link/intro.multithread">[intro.multithread]</a>) 
the corresponding successful <code class='backtick'>join()</code> return.
</p></blockquote>


<p id="res-4310"><b>Proposed resolution:</b></p>





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