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

Following up on the question in the "Update", here is a situation in which the call to f would be ambiguous (if it were allowed, that is):

// Definitions of generic "struct A", as well as "f()", are the same as above

// But additionally, consider a specialized "struct A", defined as follows:

template <>
struct A
{
    typedef A::B B;
}

// Now consider the call to "f", similarly to before:

int main()
{
    // Possibility 1 for argument to "f()"
    // A::B x;

    // Possibility 2 for argument to "f()": Use the specialized version of "struct A"
    A::B x;

    f(x); // which value to deduce for type T?  Could be "int" or "double"
}

Notice the ambiguous pair of potential instantiated functions f: Both f() and f would result in a successfull call to f().