[Bug c++/15629] New: Function overloading doesn't happen when I use friend function templates in class templates.

["ywhu at nmi dot iii dot org dot tw" <gcc-bugzilla at gcc dot gnu dot org>]

Hi,

When I use friend function templates in a class template, the function
overloading doesn't happend.

The following is the source.

==============================================================

#include <iostream>

template<int a, int b>
class T;

template<int a, int b>
void func(T<a, b> const * const t)
{
  std::cerr << "T<a, b>" << std::endl;
}

template<int a, int b>
class T
{
private:
  
  friend void func<a, b>(T<a, b> const * const t);
  friend void func<a>(T<a, 3> const * const t);
  
public:
  
  void ttt() const;
};

template<int a>
void
func(T<a, 3> const * const t)
{
  std::cerr << "T<a, 3>" << std::endl;
}


template<int a, int b>
void
T<a, b>::ttt() const
{
  func(this);
}

int
main()
{
  T<2, 3> t;
  
  t.ttt();
  
  return 0;
}

==============================================================

The error messages from gcc-3.2 is as following:

==============================================================

eee.cpp: In member function `void T<a, b>::ttt() const [with int a =
2, int b =
   3]':
eee.cpp:52:   instantiated from here
eee.cpp:44: call of overloaded `func(const T<2, 3>* const)' is
ambiguous
eee.cpp:8: candidates are: void func(const T<a, b>*) [with int a = 2,
int b =
   3]
eee.cpp:29:                 void func(const T<a, 3>*) [with int a = 2]
eee.cpp:8:                 void func(const T<a, b>*) [with int a = 2,
int b =
   3]
eee.cpp:29:                 void func(const T<a, 3>*) [with int a = 2]

==============================================================

However, when I use gcc-3.2, gcc-3.3, gcc-3.4 to compile my code, the
result is strange.

Here is my result:

1) gcc-3.2: can _not_ compile, the error message is copied and pasted
above.

2) gcc-3.3: can compile, but the result is

T<a, b>

[but I think it should be T<a, 3>]

3) gcc-3.4: can compile, but the result is

T<a, b>

[but I think it should be T<a, 3>]

< NOTE >

When I use 'struct' rather than 'class', and remove the 'friend'
declarations,
the function overloading works fine !

=============================================================
Question 2:
=============================================================

I added one more friend function declaration, and now, even gcc-3.3
doesn't compile my code.

The source code is as following:

==============================================================

#include <iostream>

template<int a, int b>
class T;

template<int a, int b>
void func(T<a, b> const * const t)
{
  std::cerr << "T<a, b>" << std::endl;
}

template<int a, int b>
class T
{
private:
  
  friend void func<a, b>(T<a, b> const * const t);
  friend void func<a>(T<a, 3> const * const t);
  friend void func<b>(T<3, b> const * const t); <-- add this -->
  
public:
  
  void ttt() const;
};

template<int a>
void
func(T<a, 3> const * const t)
{
  std::cerr << "T<a, 3>" << std::endl;
}

template<int b>  <-- add this definition -->
void
func(T<3, b> const * const t)
{
  std::cerr << "T<3, b>" << std::endl;
}

template<int a, int b>
void
T<a, b>::ttt() const
{
  func(this);
}

int
main()
{
  T<2, 3> t;
  
  t.ttt();
  
  return 0;
}

==============================================================

I can _not_ compile the code using gcc-3.2, and the error message for
gcc-3.2 is
like the one I posted above:

==============================================================

eee.cpp: In instantiation of `T<2, 3>':
eee.cpp:50:   instantiated from here
eee.cpp:19: ambiguous template specialization `func<3>' for `void
func(const
   T<3, 3>*)'
eee.cpp: In member function `void T<a, b>::ttt() const [with int a =
2, int b =
   3]':
eee.cpp:52:   instantiated from here
eee.cpp:44: call of overloaded `func(const T<2, 3>* const)' is
ambiguous
eee.cpp:8: candidates are: void func(const T<a, b>*) [with int a = 2,
int b =
   3]
eee.cpp:29:                 void func(const T<a, 3>*) [with int a = 2]
eee.cpp:8:                 void func(const T<a, b>*) [with int a = 2,
int b =
   3]
eee.cpp:29:                 void func(const T<a, 3>*) [with int a = 2]

==============================================================

Again, the following is the result when I compile it using gcc-3.2,
gcc-3.3 and gcc-3.4:

1) gcc-3.2: can _not_ compile, the error message posted above.
2) gcc-3.3: can _not_ compile, the error message just like the one
posted for gcc-3.2.
3) gcc-3.4: can compile, but the result is

T<a, b>

[but I think it should be T<a, 3>]

==============================================================

My environment:

1) Debian unstable
2) gcc-3.4.0 (Debian 20040516)
3) gcc-3.3.3 (Debian 20040422)
4) gcc-3.2.3
5) Command line options: none
6)

-- 
           Summary: Function overloading doesn't happen when I use friend
                    function templates in class templates.
           Product: gcc
           Version: 3.3.3
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ywhu at nmi dot iii dot org dot tw
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15629