GCC Bugzilla Bug 41703

Hello! I have FreeBSD 8.0-BETA4.
Why this

#include <iostream>
template <typename T, unsigned int (T::*)() const>
class TSizeEnabler { public: typedef T TClass; };

template <typename X> unsigned int GetAllSize(const X &Var)
   { return sizeof(Var); }
template <typename X> unsigned int GetAllSize(const typename TSizeEnabler<X,
&X::CalcMySize>::TClass &Var)
   { return Var.CalcMySize(); }

template <typename T>
class THash
   {
      public:
      T Var;
      unsigned int CalcMySize() const { return 42 + GetAllSize<T>(Var); }
   };
int main()
   {
      int a;
      THash<int> b;
      std::cout << GetAllSize<int>(a) << std::endl;
      std::cout << GetAllSize< THash<int> >(b) << std::endl;
      return 0;
   }


works well at gcc 3.4.6 but fails at gcc 4.2.1 and gcc 4.5.0.20091008 with
these messages:
gcc 4.5.0.2009100 output:
%g++45 -std=c++0x main.cpp
main.cpp: In function 'int main()':
main.cpp:24:46: error: call of overloaded 'GetAllSize(THash<int>&)' is
ambiguous
main.cpp:6:36: note: candidates are: unsigned int GetAllSize(const X&) [with X
= THash<int>]
main.cpp:8:36: note: unsigned int GetAllSize(const typename TSizeEnabler<X, (&
X::CalcMySize)>::TClass&) [with X = THash<int>, typename TSizeEnabler<X, (&
X::CalcMySize)>::TClass = THash<int>]
%
And gcc 4.2.1 output:
%g++ main.cpp
main.cpp: In function 'int main()':
main.cpp:23: error: call of overloaded 'GetAllSize(THash<int>&)' is ambiguous
main.cpp:5: note: candidates are: unsigned int GetAllSize(const X&) [with X =
THash<int>]
main.cpp:7: note:                 unsigned int GetAllSize(const typename
TSizeEnabler<X, (& X::CalcMySize)>::TClass&) [with X = THash<int>]
%


And how i can fix it the problem?
Thanks.

Slightly reduced:

template <typename T, int (T::*)() const>
struct TSizeEnabler
{
    typedef T TClass;
};

template <typename X>
int
GetAllSize(const X &Var)
{ return sizeof(Var); }

template <typename X>
int
GetAllSize(const typename TSizeEnabler<X, &X::func>::TClass &Var)
{ return Var.func(); }

struct H
{
    int func() const;
};

int main()
{
    H b;
    return GetAllSize< H >(b);
}

I think you're right that this is a bug.  As a workaround you might be able to
remove GetAllSize(const X &Var) from the overload set for the case when
X::CalcMySize exists.

Subject: Bug 41703

Author: jason
Date: Fri Nov  6 03:32:55 2009
New Revision: 153957

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=153957
Log:
        PR c++/41703
        * pt.c (check_undeduced_parms): New subroutine of...
        (more_specialized_fn): ...here.  Undeduced template parms can make
        a template less specialized than another.

Added:
    trunk/gcc/testsuite/g++.dg/template/partial6.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/pt.c
    trunk/gcc/testsuite/ChangeLog

Fixed for 4.5.