Purpose of IsA() method

ROOT
1

Hi,

Pardon the naive question, I’m trying to see if there is something more complex here that escapes me.

What is exactly the purpose of the IsA() method? I understand that when we say

if(obj->IsA() == MyClass::Class())

we test if obj is of type MyClass.

I can think that this can be used with inheritance (or multiple inheritance) where a pointer may be pointing to more than one types. If that’s the case, then this is very similar to a dynamic_cast operation. Then, why go into the trouble of introducing the IsA() method?

–Christos

2

Hi Christos,
there’s a fundamental difference between dynamic_cast and IsA:

TH1F* h2=new TH1F("h","h",10,0.,1.); if (dynamic_cast<TH1*>(h2) && h2->IsA()!=TH1::Class()) std::cout<<"dynamic_cast and IsA() are different." << std::endl;
Also, IsA() gives access to the Cint’s RTTI, dynamic_cast does not. But if you know your compiler supports dynamic_cast, and you don’t need Cint’s RTTI, then use dynamic_cast wherever you can.
Cheers, Axel.