<HTML>
<HEAD>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<TITLE>
    CWG Issue 1828</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="1828"></A><H4>1828.
  
<I>nested-name-specifier</I> ambiguity
</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>Richard Smith
 &#160;&#160;&#160;

 <B>Date: </B>2014-01-08<BR>


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



<P>
<A HREF="125.html">Issue 125</A> concerned an example like</P>

<PRE>
  friend A::B::C();
</PRE>

<P>which might be parsed as either</P>

<PRE>
  friend A (::B::C)();
</PRE>

<P>or</P>

<PRE>
  friend A::B (::C)();
</PRE>

<P>Its resolution attempted to make such constructs unambiguously
ill-formed by allowing any identifier, not just namespaces and types,
to appear in a <I>nested-name-specifier</I>, apparently on the
assumption that <TT>C</TT> in this case would become part of an
ill-formed <I>nested-name-specifier</I> instead of being taken as
the <I>unqualified-id</I> in a <I>qualified-id</I>.  Unfortunately,
the current specification does not implement that intent, leaving
both parses as valid possibilities.</P>

<P>A different approach might be to adjust the specification of the
lookup of names appearing in <I>nested-name-specifier</I>s from</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.  If the name found does not
designate a namespace or a class, enumeration, or dependent
type, the program is ill-formed.

</BLOCKQUOTE>

<P>to</P>

<BLOCKQUOTE>

Lookup of an <I>identifier</I> followed by a <TT>::</TT>
scope resolution operator considers only namespaces, types, and
templates whose specializations are types.  If an <I>identifer</I>,
<I>template-id</I>, or <I>decltype-specifier</I> is followed by
a <TT>::</TT> scope resolution operator, the name shall designate
a namespace, class, enumeration, or dependent type, and shall form
part of a <I>nested-name-specifier</I>.

</BLOCKQUOTE>

<P>This approach would also remove the need for deferred lookup
for <I>template-id</I>s and thus resolve
<A HREF="1771.html">issue 1771</A>.</P>

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