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    CWG Issue 782</TITLE>
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<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="782"></A><H4>782.
  
Lambda expressions and argument-dependent lookup
</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>Mike Miller
 &#160;&#160;&#160;

 <B>Date: </B>1 March, 2009<BR>


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

<P>Functions and function objects behave differently with respect to
argument-dependent lookup.  In particular, the associated namespaces
of a function's parameters and return types, but not the namespace
in which the function is declared, are associated namespaces of the
function; the exact opposite is true of a function object.  The
Committee should consider rectifying that disparity; however, in
the absence of such action, an explicit decision should be made as
to whether lambdas are more function-like or object-like with respect
to argument-dependent lookup.  For example:</P>

<PRE>
    namespace M {
      struct S { };
    }
    namespace N {
      void func(M::S);
      struct {
        void operator()(M::S);
      } fn_obj;
      const auto&amp; lambda = [](M::S){};
    }
    void g() {
      f(N::func);    // assoc NS == M, not N
      f(N::fn_obj);  // assoc NS == N, not M
      f(N::lambda);  // assoc NS == ??
    }
</PRE>

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

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

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