Re: Confused about friends in template class

According to:
http://www.parashift.com/c++-faq-lite/templates.html#faq-35.4
, if my understanding is correct, in

template<typename T>
class Foo {
   friend void func (const Foo<T>& foo);
};

template<typename T>
void func (const Foo<T>& foo) { ... }

func is seen as a non-template function at class instantation time,
and the func function template is never actually instantieted, so the
linker error (the compiler is searching the ordinary one).

The proposed solution is via forward declaration, but (in VC 8) this
works:

template<typename T>
class Foo {

  template<typename T>
  friend void func (const Foo<T>& foo);
};

template<typename T>
void func (const Foo<T>& foo) { ... }

However gcc complains about the fact that T (of func) shadows T (of
Foo), but the following works:

template<typename T>
class Foo {

  template<typename U>
  friend void func (const Foo<U>& foo);
};

template<typename T> // Or U, indifferent right?
friend void func (const Foo<T>& foo);

According to a book of mine (maybe outdated, 2002) it seems that the
difference between this last option and the one proposed in the guide
is that here func can be a friend of classes with different templates,
like:
func<A> friend of Foo<B>
while in the solution proposed in the guide this can not happend.

My intuition (probably wrong) is than that the "invalid VC syntax"
really means to the VC compiler the situation illustrated in the guide
via forward declaration, but this syntax is illegal according to the
standard.
Too bad, I liked this more concise solution :)

Anyway, if my understanding was correct, there are reasons to avoid
using always the last option, where the function is also a friend of
instantation of the class with different parameters?

Cheers
StephQ