C++: nested class of a template class

Question

Consider the following code:

template < typename T >
struct A
{
    struct B { };
};

template < typename T >
void f( typename A::B ) {          


        

Answer 1

How can I avoid explicitly specifying int while calling f?

Just make B declare its nesting class type

template < typename T >
struct A
{
    struct B { typedef A outer; };
};

Then you can deduce it. The following takes the outer template, the inner's typedef and a return type

template class Outer, typename D, typename R = void >
struct nesting { };

template class Outer, typename Arg, typename R>
struct nesting< Outer, Outer, R > {
  typedef Arg arg1_type;
  typedef R type;
};

template < typename T >
typename nesting::type
f(T) { 
  /* nesting::arg1_type is A's T */ 
}