Get type of child class at runtime without RTTI in C++ from base pointer

Question

I have the problem that i need to check if a given type is the same as one specific one.

Simple example:

class Base {
   public:
    virtual void hi() = 0;
};

class A : public Base {
   public:
    void hi() { printf("Hi! I am A\n"); }
};

class B : public Base {
   public:
    void hi() { printf("Hi! I am B\n"); }
};

void isA(Base* something) {
    // 1
    if (something.is(A)) {
        A* aSomething = (A*)something;
        aSomething->hi();
    }

    // 2
    something->hi();
}

Output:

Hi! I am A
Hi! I am A

The problem is that i have no RTTI enabled (and can't enable it) so i do not have dynamic_cast or typeid(...). But the program somehow still knows which type it is, as the part after // 2 still works correctly including polymorphism.

In my exact scenareo, A is a template. So i only need to check if the given pointer to the base is of type A with the same template arguments.