gistfile1.cpp

struct Super {
    virtual Super* id() {
        return this;
    }
};

struct X : Super {};
struct Y : Super {};

template <typename A>
A* id(A* a) {
    return a;
}

// if you have an X* called x and a Y* called y, then:
// id(x) is shorthand for id<X>(x), and id(y) is shorthand for id<Y>(y), this is type inference at play.
// id(x) is of type X*. id(y) is of type Y*. This is easy to see, you just substitute in X or Y into the template
// That's why it's called a template.

// if you call x->id() then you get a Super. if you call y->id() then you get a Super. 
// this is because you are calling the function Super::id.