A bug in namespaced template overloaded operator << and >>

[Topi Maenpaa <topiolli at ees2 dot oulu dot fi>]

Hi,

I have had some weird problems in template overloaded functions that are
enclosed in a namespace. I have produced a simplified version of the
structure I have been trying to compile. For this code, g++ says:

Test5.cc: In function `int main()':
Test5.cc:68: ambiguous overload for `_IO_ostream_withassign & <<
foo::rgbcolorimage &'
Test5.cc:36: candidates are: class ostream & foo::operator
<<<foo::rgbcolor>(ostream &, foo::matrix<foo::rgbcolor> &)
Test5.cc:47:                 class ostream & foo::operator
<<<foo::rgbcolor>(ostream &, foo::image<foo::rgbcolor> &)
Test5.cc:55:                 class ostream & foo::operator
<<<foo::rgbcolor>(ostream &, foo::image<foo::rgbcolor> &)

After a few days of wasted time I got it work by removing the "namespace
foo" and "using namespace foo". Since this was not an acceptable
solution to me, I figured out another way: you can do it by moving the
template definitions for operator << (ostream, color<T,i>) and operator
<< (ostream, image<T>) *before* the definitions of class rgbcolor and
rgbcolorimage, respectively. (Guess how long it took? Enough to drive me
crazy...)


---------8<---- Test5.cc ----8<---------

#include <iostream>

namespace foo
{
	template <class T, int i>
	class color
	{
	public:
		template <class U, int j> friend ostream& operator << (ostream& sout,
color<U,j>& obj);
	};

	class rgbcolor : public color<int,3>
	{
	};

	template <class T, int i> ostream& operator << (ostream& sout,
color<T,i>& obj)
	{
		sout << i;
		return sout;
	}





	template <class T>
	class matrix
	{
	public:
		template <class U> friend ostream& operator << (ostream& sout,
matrix<U>& obj);
	protected:
		T element;
	};

	template <class T> ostream& operator << (ostream& sout, matrix<T>& obj)
	{
		sout << obj.element;
		return sout;
	}


	

	template <class T>
	class image : public matrix<T>
	{
	public:
		template <class U> friend ostream& operator << (ostream& sout,
image<U>& obj);
	};

	class rgbcolorimage : public image<rgbcolor>
	{
	};

	template <class T> ostream& operator << (ostream& sout, image<T>& obj)
	{
		sout << obj.element;
		return sout;
	}

}

using namespace foo;


int main(void)
{
	rgbcolorimage img;
	cout << img;
}


-- 
-Topi-
 << http://ee.oulu.fi/~topiolli >>