[Bug c++/15629] Function templates, overloads, and friend name injection

["bangerth at dealii dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From bangerth at dealii dot org  2004-05-24 15:19 -------
OK, something is really screwed up here. Take this: 
----------------- 
#include <iostream> 
#define PRINT std::cerr << __PRETTY_FUNCTION__ << std::endl 
 
template<int a, int b> class T; 
 
template<int a, int b> void func(T<a, b> * t) { PRINT; } 
template<int a>        void func(T<a, 3> * t) { PRINT; } 
 
template<int a, int b> struct T { 
    friend void func<a, b>(T<a, b> * t); 
    friend void func<a>   (T<a, 3> * t); 
   
    void foo(); 
}; 
 
template<int a, int b> void T<a, b>::foo() { 
  func((T<2,3>*)0); 
} 
 
int main() { 
  func((T<2,3>*)0); 
  T<2,3>().foo(); 
} 
----------------------- 
 
Note that the call to func in main() is the same as the one in foo(), so 
it should really yield the same result. Alas, with gcc3.4, we get: 
 
g/x> /home/bangerth/bin/gcc-3.4-pre/bin/c++ x.cc ; ./a.out 
void func(T<a, 3>*) [with int a = 2] 
void func(T<a, b>*) [with int a = 2, int b = 3] 
 
On the other hand, if we revert the order of the two calls in main(), we get 
a different result, namely a call to the general T<a,b> template as in the 
second line above. My inclination is to say that this is due to the fact that 
we only instantiate T<2,3> in the second call in main(), since the cast 
to (T<2,3>*)0 does not require instantiation of the template. Now, how that 
can affect the result I don't know -- presumably it has something to do with 
injecting the friend functions into the global namespace. This explains 
why reverting the calls in main() changes the result. 
 
What evades me, however, is why injecting the names should make any 
difference? Note that if I remove the friend declarations altogether, 
then we get two calls to the <a,3> template, irrespective of the call 
order in main(). I tend to think that this is what we should get in all 
cases, but would like to have a second opinion... 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Function overloading doesn't|Function templates,
                   |happen when I use friend    |overloads, and friend name
                   |function templates in class |injection
                   |templates.                  |


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