Call child method with reinterpret_cast or not ?

[Krogoth]

I have class A and method a().
I have class B : public A and new method b().
I can call b from A like
reinterpret_cast<B*>(this)->b();
If I am 100% sure that this A instance is B, not just A, is it
1) always safe to do like this?
2) faster than virtual call?

[ne555]

¿why is your base class aware of its derived classes?

[Krogoth]

I can ask, but it has no Talk method. :[

You say it's safe for sure, did I get you right?

[JLBorges]

> reinterpret_cast<B*>(this)->b();
> If I am 100% sure that this A instance is B, not just A, is it

> 1) always safe to do like this?

No, it is not safe.

If it is guaranteed that the dynamic type of the object pointed to by this is B or a derived class of B (and B does not inherit virtually from A), static_cast<B*>(this)->b(); is safe.


> 2) faster than virtual call?

Yes. Particularly if B::b() is inlineable. Marginally otherwise.

[Krogoth]

Thank u!
I don't see any real use of it in my plans though.))
(This is not much useful at all)

[JLBorges]

> This is not much useful at all

True.

With polymorphic classes: favour virtual functions over casts of any kind, dynamic_cast over static_cast

With any type: favour static_cast over reinterpret_cast