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?

You'll need a little help from struct B.

template < typename T >
struct A
{
    struct B 
    { 
        static T getType(); // no impl required 
    };
};

#define mytypeof(T) (true?0:T)

template < typename T, typename U >
void f( T t, U ) { } // U will be T of A::B

Calling it with the following:

f(x, mytypeof(x.getType()));

Alternatively, you could abstract mytypeof(x.getType()) away by introducing another function which f calls, so you could have your original f(x). e.g.

template < typename T, typename U >
void b( T t, U ) { } // U will be T of A::B

template < typename T >
void f( T t )
{
    b(t, mytypeof(t));
}

You could then call f(x).