<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 1913</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="1913"></A><H4>1913.
  
<TT>decltype((x))</TT> in <I>lambda-expression</I>s
</H4>
<B>Section: </B>7.5.6&#160; [<A href="https://wg21.link/expr.prim.lambda">expr.prim.lambda</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD5
 &#160;&#160;&#160;

 <B>Submitter: </B>Dinka Ranns
 &#160;&#160;&#160;

 <B>Date: </B>2014-04-15<BR>


<P><B>[Accepted as a DR as part of paper P0588R1 at the
October, 2017 meeting.]</B></P>



<P>According to 7.5.6 [<A href="https://wg21.link/expr.prim.lambda#19">expr.prim.lambda</A>] paragraph 19,</P>

<BLOCKQUOTE>

Every occurrence of <TT>decltype((x))</TT> where <TT>x</TT> is a possibly
parenthesized <I>id-expression</I> that names an entity of automatic
storage duration is treated as if <TT>x</TT> were transformed into an
access to a corresponding data member of the closure type that would have
been declared if <TT>x</TT> were an odr-use of the denoted entity.

</BLOCKQUOTE>

<P>This formulation is problematic because it assumes that <TT>x</TT>
can be captured and, if captured, would result in a member of the
closure class.  The former is not true if the lambda has no
<I>capture-default</I>, and the latter is not guaranteed if the
<I>capture-default</I> is <TT>&amp;</TT>.</P>

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