Re: c++/9558: subclass cannot find parent members without explicit "this->" in some cases

[Wolfgang Bangerth <bangerth@ticam.utexas.edu>]

The following reply was made to PR c++/9558; it has been noted by GNATS.

From: Wolfgang Bangerth <bangerth@ticam.utexas.edu>
To: "Ryan C. Gordon" <ryan@epicgames.com>
Cc: gcc-bugs@gcc.gnu.org, <gcc-gnats@gcc.gnu.org>, <mark@codesourcery.com>
Subject: Re: c++/9558: subclass cannot find parent members without explicit
 "this->" in some cases
Date: Mon, 3 Feb 2003 20:43:26 -0600 (CST)

 > After thinking about it, (and based on the initial response of "can we 
 > add this as a FAQ to non-bugs"), 
 
 ...which I just took care of...
 
 > perhaps the problem is in the error 
 > message more than the behaviour. My assumption was this was a problem in 
 > the new parser and that it wasn't resolving because something had 
 > confused it. Is there a way to differentiate between this and a variable 
 > that absolutely positively does not exist, and issue a different error 
 > message? I think that would at least stop more incorrect bug reports on 
 > the issue.
 
 It's hard to come up with something reasonable, because of cases like
 
   template <typename T> struct A        { int i;               };
   template <typename T> struct B : A<T> { int f() {return i;}  };
   template <>           struct A<int>   {                      }; // oops
 
 In B::f, what is the compiler supposed to tell you? I guess one would like 
 to have something like
   Error: "i" undeclared (did you mean "this->i" or A<T>::i"?)
 
 The gotcha comes in the specialization of A<int>: there really is no "i" 
 in this class.
 
 There are worse cases, like 
   template <typename T> struct B : typename A<T>::some_typedef {...};
 where you really have no idea what the base class might be, unless you 
 actually instantiate it.
 
 Of course, this doesn't mean that Mark or someone else has ingeneous ideas 
 for warnings...
 
 W.
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth             email:            bangerth@ticam.utexas.edu
                               www: http://www.ticam.utexas.edu/~bangerth/