How to declare a templated struct/class as a friend?

Question

I'd like to do the following:

template <typename T> struct foo {     template <typename S>     friend struct foo<S>;  private:     // ... }; 

but my compiler (VC8) chokes on it:

error C3857: 'foo<T>': multiple template parameter lists are not allowed 

I'd like to have all possible instantiations of template struct foo friends of foo<T> for all T.

How do I make this work ?

EDIT: This

template <typename T> struct foo {     template <typename>     friend struct foo;  private:     // ... }; 

seems to compile, but is it correct ? Friends and templates have very unnatural syntax.

Answer 1

template<typename> friend class foo 

this will however make all templates friends to each other. But I think this is what you want?