<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 1697</TITLE>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<STYLE TYPE="text/css">
  INS { text-decoration:none; font-weight:bold; background-color:#A0FFA0 }
  .INS { text-decoration:none; background-color:#D0FFD0 }
  DEL { text-decoration:line-through; background-color:#FFA0A0 }
  .DEL { text-decoration:line-through; background-color: #FFD0D0 }
  @media (prefers-color-scheme: dark) {
    HTML { background-color:#202020; color:#f0f0f0; }
    A { color:#5bc0ff; }
    A:visited { color:#c6a8ff; }
    A:hover, a:focus { color:#afd7ff; }
    INS { background-color:#033a16; color:#aff5b4; }
    .INS { background-color: #033a16; }
    DEL { background-color:#67060c; color:#ffdcd7; }
    .DEL { background-color:#67060c; }
  }
  SPAN.cmnt { font-family:Times; font-style:italic }
</STYLE>
</HEAD>
<BODY>
<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="1697"></A><H4>1697.
  
Lifetime extension and copy elision
</H4>
<B>Section: </B>6.8.7&#160; [<A href="https://wg21.link/class.temporary">class.temporary</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD4
 &#160;&#160;&#160;

 <B>Submitter: </B>Richard Smith
 &#160;&#160;&#160;

 <B>Date: </B>2013-06-01<BR>


<P>[Adopted as paper P0135R1 at the June, 2016 meeting.]</P>



<P>In an example like,</P>

<PRE>
  struct S { ~S(); };
  struct X { X(); X(const X&amp;); };
  struct T { S &amp;&amp;s; X x; };
  void f();
  void g() { T t = T{ {}, {} }; f(); }
</PRE>

<P>it appears that the current wording allows two ways of handling
this:</P>

<OL>
<LI><P>The copy to <TT>t</TT> in <TT>g</TT> is not elided. <TT>X(const
X&amp;)</TT> is called, then <TT>~S()</TT> is called, then <TT>f()</TT> is
called.</P></LI>

<LI>The copy to <TT>t</TT> in <TT>g</TT> is elided, so the temporary
and <TT>t</TT> are the same object. Thus, the <TT>S</TT> object's lifetime
is extended to the lifetime of the reference <TT>t.s</TT>, so
first <TT>f()</TT> is called, then <TT>~S()</TT> is called (and <TT>X(const
X&amp;)</TT> is not called).</LI>

</OL>

<P>However, EDG and g++ produce a third behavior: they do not call
<TT>X(const X&amp;)</TT>, but they destroy the <TT>S()</TT> temporary at
the end of its full-expression. The current wording does not appear to
permit this behavior, but it seems preferable that lifetime extension does
not depend on whether copy elision is done.</P>

<BR><BR>
</BODY>
</HTML>
