Re: c++/950: Template lookup problem

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

The following reply was made to PR c++/950; it has been noted by GNATS.

From: Wolfgang Bangerth <bangerth@ticam.utexas.edu>
To: gcc-bugs@gcc.gnu.org, <gcc-gnats@gcc.gnu.org>
Cc:  
Subject: Re: c++/950: Template lookup problem
Date: Sun, 10 Nov 2002 14:46:04 -0600 (CST)

 A reduced testcase for this one is
 --------------------------------------------
 struct B { void a (int n); };
 struct D: public B {};
 
 template <typename T> struct X {
     template<typename Y>
     static void foo (const Y&, void (T::*)(Y));
 };
 
 int main () {
   int n = 3;
   X<D>::foo(n, &D::a);
 }
 --------------------------------------
 The error I get is this one:
 x.cc: In function `int main()':
 x.cc:11: error: no matching function for call to `X<D>::foo(int&, void
    (B::*)(int))'
 
 Thus, the compiler cannot find a match for X::foo, since &D::a is 
 immediately converted to &B::a, i.e. to a pointer to member function of 
 the _base_ class, although we have taken a p-t-m-f of the derived class. I 
 don't know what the standard says on this one, but at least the failure 
 mode is clear now.
 
 The problem can be worked around using a temporary variable of type 
   void (D::*)(int)
 or an explicit cast.
 
 Regards
   Wolfgang
 
 -------------------------------------------------------------------------
 Wolfgang Bangerth              email:           bangerth@ticam.utexas.edu
                                www: http://www.ticam.utexas.edu/~bangerth