gistfile1.cpp

template <class A>
class Outer {
public:
    template <class B>
    class Inner {
    public:
        template <class C>
		void foo(Outer<C>::template Inner<C> innerC) { }
    };

    Inner<A> inner;
};

class X {};
class Y {};

int main() {
    Outer<X> outerX;
    Outer<Y> outerY;
    outerX.inner.foo<Y>(outerY.inner);
}