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    CWG Issue 2259</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="2259"></A><H4>2259.
  
Unclear context describing ambiguity
</H4>
<B>Section: </B>9.3.3&#160; [<A href="https://wg21.link/dcl.ambig.res">dcl.ambig.res</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++17
 &#160;&#160;&#160;

 <B>Submitter: </B>Richard Smith
 &#160;&#160;&#160;

 <B>Date: </B>2016-04-12<BR>


<P>[Adopted at the February/March, 2017 meeting.]</P>



<P>According to 9.3.3 [<A href="https://wg21.link/dcl.ambig.res#3">dcl.ambig.res</A>] paragraph 3,</P>

<BLOCKQUOTE>

Another ambiguity arises in a <I>parameter-declaration-clause</I> of a
function declaration, or in a <I>type-id</I> that is the operand of a
<TT>sizeof</TT> or <TT>typeid</TT> operator, when a <I>type-name</I> is
nested in parentheses.

</BLOCKQUOTE>

<P>There are two problems here: first,
a <I>parameter-declaration-clause</I> appears in
a <I>lambda-expression</I>, not just in a function declaration.  Second,
the ambiguity can arise in a <I>type-id</I> appearing in any context, not
just in a <TT>sizeof</TT> or <TT>typeid</TT> expression.</P>

<P><B>Proposed resolution (January, 2017):</B></P>

<P>Change 9.3.3 [<A href="https://wg21.link/dcl.ambig.res#3">dcl.ambig.res</A>] paragraph 3 as follows:</P>

<BLOCKQUOTE>

Another ambiguity arises in a <I>parameter-declaration-clause</I> <DEL>of a
function declaration, or in a <I>type-id</I> that is the operand of a
<TT>sizeof</TT> or <TT>typeid</TT> operator</DEL>, when a <I>type-name</I>
is nested in parentheses. In this case, the choice is between the
declaration of a parameter of type pointer to function and the declaration
of a parameter with redundant parentheses around
the <I>declarator-id</I>. The resolution is to consider
the <I>type-name</I> as a <I>simple-type-specifier</I> rather than
a <I>declarator-id</I>. [<I>Example:</I>...

</BLOCKQUOTE>

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