Class templates and friend function templates

[BigMan]

I have a class template like this:

template< typename t >
class c;

I'd also like to have an operator == for objects of types, which are
different specializations of c:

template< typename t1, typename t2 >
bool operator ==
(
s< t1 > const&
, s< t2 > const&
);

In order to implement this operator, I need it to be a friend of both
s< t1 > and s< t2 >. For the sake of safety, I'd like no other
specialization of c to have this operator as its friend. Is this
possible and, if so, how?

 

[Ian]

I have a class template like this:

template< typename t >
class c;

I'd also like to have an operator == for objects of types, which are
different specializations of c:

template< typename t1, typename t2 >
bool operator ==
(
s< t1 > const&
, s< t2 > const&
);

In order to implement this operator, I need it to be a friend of both
s< t1 > and s< t2 >. For the sake of safety, I'd like no other
specialization of c to have this operator as its friend. Is this
possible and, if so, how?

Why? What harm can a public operator == do?

Ian