<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 766</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="766"></A><H4>766.
  
Where may lambda expressions appear?
</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>CD2
 &#160;&#160;&#160;

 <B>Submitter: </B>Daveed Vandevoorde
 &#160;&#160;&#160;

 <B>Date: </B>6 February, 2009<BR>


<P>[Voted into the WP at the July, 2009 meeting as part of N2927.]</P>

<P>According to 7.5.6 [<A href="https://wg21.link/expr.prim.lambda#7">expr.prim.lambda</A>] paragraph 7, the appearance of
a lambda expression results in the definition of a class &#8220;considered
to be defined at the point where the lambda expression occurs.&#8221;  It
is not clear whether that means that a lambda expression cannot appear
at any point where it is not permitted to define a class type.  For
example, 9.3.4.6 [<A href="https://wg21.link/dcl.fct#10">dcl.fct</A>] paragraph 10 says, &#8220;Types shall
not be defined in return or parameter types.&#8221;  Does that mean that
a function declaration like</P>

<PRE>
    void f(int a[sizeof ([]{ return 0; })]);
</PRE>

<P>is ill-formed, because the parameter type defines the closure class
for the lambda expression? (<A HREF="686.html">Issue 686</A> lists
many contexts in which type definitions are prohibited.  Each of these
should be examined to see whether a lambda expression should be allowed
or prohibited there.)</P>

<P><B>Proposed resolution (July, 2009)</B></P>

<P>See document PL22.16/09-0117 = WG21 N2927.</P>

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