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    CWG Issue 1837</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="1837"></A><H4>1837.
  
Use of <TT>this</TT> in <TT>friend</TT> and local class declarations
</H4>
<B>Section: </B>_N4567_.5.1.1&#160; [<A href="https://wg21.link/expr.prim.general">expr.prim.general</A>]
 &#160;&#160;&#160;

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

 <B>Submitter: </B>Hubert Tong
 &#160;&#160;&#160;

 <B>Date: </B>2014-01-13<BR>


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



<P>The description of the use of <TT>this</TT> found in
_N4567_.5.1.1 [<A href="https://wg21.link/expr.prim.general">expr.prim.general</A>] paragraphs 3 and 4 allow it to appear
in the declaration of a non-static member function following the
optional <I>cv-qualifier-seq</I> and in the
<I>brace-or-equal-initializer</I> of a non-static data member; all
other uses are prohibited.  These restrictions appear to allow
questionable uses of <TT>this</TT> in several contexts. For example:</P>

<PRE>
  template &lt;typename T&gt;
  struct Fish { static const bool value = true; };

  struct Other {
    int p();
    auto q() -&gt; decltype(p()) *;
  };

  class Outer {
    //<SPAN CLASS="cmnt"> The following declares a member function of class </SPAN>Other.
    //<SPAN CLASS="cmnt"> Is </SPAN>this<SPAN CLASS="cmnt"> interpreted as </SPAN>Other*<SPAN CLASS="cmnt"> or </SPAN>Outer*<SPAN CLASS="cmnt">?</SPAN>
    friend auto Other::q() -&gt; decltype(this-&gt;p()) *;
    int g();
    int f() {
     extern void f(decltype(this-&gt;g()) *);
     struct Inner {
       //<SPAN CLASS="cmnt"> The following are all within the declaration of </SPAN>Outer::f().
       //<SPAN CLASS="cmnt"> Is </SPAN>this Outer*<SPAN CLASS="cmnt"> or </SPAN>Inner*<SPAN CLASS="cmnt">?</SPAN>
       static_assert(Fish&lt;decltype(this-&gt;g())&gt;::value, "");
       enum { X = Fish&lt;decltype(this-&gt;f())&gt;::value };
       struct Inner2 : Fish&lt;decltype(this-&gt;g())&gt; { };
       friend void f(decltype(this-&gt;g()) *);
       friend auto Other::q() -&gt; decltype(this-&gt;p()) *;
     };
     return 0;
    }
  };
</PRE>

<PRE>
  struct A {
   int f();
   bool b = [] {
    struct Local {
     static_assert(sizeof this-&gt;f() == sizeof(int), ""); // A<SPAN CLASS="cmnt"> or </SPAN>Local<SPAN CLASS="cmnt">?</SPAN>
    };
   };
  };
</PRE>

<P>There is implementation divergence on the treatment of these
examples.</P>

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