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    CWG Issue 2653</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="2653"></A><H4>2653.
  
Can an explicit object parameter have a default argument?
</H4>
<B>Section: </B>9.3.4.6&#160; [<A href="https://wg21.link/dcl.fct">dcl.fct</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++23
 &#160;&#160;&#160;

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

 <B>Date: </B>2022-11-03
  &#160;&#160;&#160;
  <B>Liaison: </B>EWG<BR><BR>


<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2720r0.pdf#GB051">P2720R0 comment
  GB&#160;051<BR></A>

<P>[Accepted at the November, 2022 meeting.]</P>

<P>
The syntax and semantics appear to allow:
<PRE>
  struct S { void f(this const S&amp; = S{}); };
</PRE>

This is probably no more than an oddity, but perhaps it should be prevented.
</P>

<P><B>Proposed resolution (approved by CWG 2022-11-08):</B></P>

<P>Change in 9.3.4.6 [<A href="https://wg21.link/dcl.fct#3">dcl.fct</A>] paragraph 3 as follows:</P>

<PRE>
<I>parameter-declaration:
    attribute-specifier-seq<SUB>opt</SUB></I> this<SUB>opt</SUB> <I>decl-specifier-seq declarator
    attribute-specifier-seq<SUB>opt</SUB></I> <DEL>this<SUB>opt</SUB></DEL> <I>decl-specifier-seq declarator = initializer-clause
    attribute-specifier-seq<SUB>opt</SUB></I> this<SUB>opt</SUB> <I>decl-specifier-seq abstract-declarator<SUB>opt</SUB>
    attribute-specifier-seq<SUB>opt</SUB></I> <DEL>this<SUB>opt</SUB></DEL> <I>decl-specifier-seq abstract-declarator<SUB>opt</SUB> = initializer-clause</I>
</PRE>

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