Bug#312362: g++-4.0: friend is ineffective in namespace

[Philip Martin <philip@codematters.co.uk>]

Fumitoshi UKAI <ukai@debian.or.jp> writes:

> I think this is a bug of g++-4.0.

No, it's a documented change in behaviour.  From
http://gcc.gnu.org/gcc-4.0/changes.html

  * Friends of classes defined outside their namespace are correctly handled:

   namespace N {
     class A;
   }
   class N::A {
     friend class B; // Refer to N::B in GCC 4.0.0
                     // but ::B in earlier versions of GCC
   };

> It can be reprodusible by this code:
>
>  % cat a.cc
>  namespace ns {
>  	class A;
>  };
>  class ns::A {
>   public:
> 	A(int j) { i = j; };
>   private: int i;
> 	 friend A operator+(const A& x, const A& y);

ns::operator+ in gcc-4, ::operator+ in earlier versions.

>  };
>  using namespace ns;
>  A operator+(const A& x, const A& y) {
> 	return A(x.i + y.i);
>  }

This is ::operator+ which is not a friend in gcc-4.  If you use

A ns::operator+(const A& x, const A& y) {
	return A(x.i + y.i);
}

you define the friend and it will compile, but I don't know if that's
what you want.  If you want to make ::operator+ a friend in gcc-4 use
something like

namespace ns {
 	class A;
};
ns::A operator+(const ns::A& x, const ns::A& y);
class ns::A {
 public:
	A(int j) { i = j; };
 private: int i;
	 friend A (::operator+)(const A& x, const A& y);
};
using namespace ns;
A operator+(const A& x, const A& y) {
	return A(x.i + y.i);
}

-- 
Philip Martin