Member function of nested class returns type of nested class

Question

I have a struct within a class like this

template <class T>
class a {
    struct b {
        int var;
        b *foo(const T&);
    };
    int var;
};

and I want to define foo outside of struct b.

How do I do that?

Answer 1

template <class T>
typename a<T>::b* a<T>::b::foo(const T&)
{
    //code
}