Polymorphic objects on the stack?

Question

In Why is there no base class in C++?, I quoted Stroustrup on why a common Object class for all classes is problematic in c++. In that quote there is the statement:

Answer 1

I think the point is that this is not "really" polymorphic (whatever that means :-).

You could write your test function like this

template
void test(T& obj)
{
    obj.f();
}

and it would still work, whether the classes have virtual functions or not.