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    CWG Issue 1771</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="1771"></A><H4>1771.
  
Restricted lookup in <I>nested-name-specifier</I>
</H4>
<B>Section: </B>6.5.5&#160; [<A href="https://wg21.link/basic.lookup.qual">basic.lookup.qual</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD6
 &#160;&#160;&#160;

 <B>Submitter: </B>Canada
 &#160;&#160;&#160;

 <B>Date: </B>2013-09-24<BR><BR>


<P>[Accepted at the November, 2020 meeting as part of paper P1787R6 and
moved to DR at the February, 2021 meeting.]</P>

<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3903.html#CA21">N3690 comment
  CA&#160;21<BR></A>

<P>Consider the following example:</P>

<PRE>
  template &lt;typename T&gt; struct B { };
  namespace N {
    namespace L {
      template &lt;int&gt; void A();
    }
    namespace M {
      template &lt;int&gt; struct A { typedef int y; };
    }
    using namespace L;
    using namespace M;
  }
  B&lt;N::/*template */A&lt;0&gt;::y&gt; (x);
</PRE>

<P>Which <TT>A</TT> is referenced in the last line?  According to
6.5.5 [<A href="https://wg21.link/basic.lookup.qual#1">basic.lookup.qual</A>] paragraph 1,</P>

<BLOCKQUOTE>

If a <TT>::</TT> scope resolution operator in
a <I>nested-name-specifier</I> is not preceded by
a <I>decltype-specifier</I>, lookup of the name preceding that
<TT>::</TT> considers only namespaces, types, and templates whose
specializations are types.

</BLOCKQUOTE>

<P>It is not clear whether this applies to the example or not,
and the interpretation of the <TT>&lt;</TT> token depends on the
result of the lookup.</P>

<P><B>Notes from the September, 2013 meeting:</B></P>

<P>The restricted lookup mentioned in 6.5.5 [<A href="https://wg21.link/basic.lookup.qual#1">basic.lookup.qual</A>] paragraph 1
is based on a one-token lookahead; because the next
token following <TT>A</TT> in the example is not <TT>::</TT>,
the restricted lookup does not apply, and the result is ambiguous.
Uncommenting the <TT>template</TT> keyword in the example does not
affect the lookup.</P>

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