How to check if two objects inherit from the same base class?

Question

I'm trying to override Object::Equals in C++ .NET but I'm running into some difficulties

virtual bool IState::Equals(Object^ o) override{
     if (o->GetType() == IState::typeid){
      IState^ s = (IState^) o;
      if (s->type == this->type &&
       s->target_state == this->target_state &&
       s->current_state == this->current_state){
       return true;
      }
      else{
       return false;
      }
     }
     return false;
    }

This code works fine if o is and IState. However, I inherit from IState with State. I'd like my Equals function to return true if I pass a State with the same content.

I get that State is not the same as IState, but is there an operator which will allow me to check if they inherit from the same base class? Maybe overloading the operator typeid might help, but it seems like a lot of trouble for that

Answer 1

How about using the typeid operator? http://msdn.microsoft.com/en-us/library/fyf39xec(VS.80).aspx

Answer 2

Is using reflection an option? If so, take a look at the Type::IsAssignableFrom() method, and the Type::BaseType property.

Answer 3

Ok I managed to get it to work

I was missing the ->BaseType() after the ->GetType()

here is the working version

virtual bool IState::Equals(Object^ o) override{
        if (o->GetType()->BaseType() == IState::typeid){
                IState^ s = (IState^) o;
                if (s->type == this->type &&
                        s->target_state == this->target_state &&
                        s->current_state == this->current_state){
                        return true;
                }
                else{
                        return false;
                }
        }
        return false;
    }

thank you all for your time, support and devotion =)

Answer 4

The correct way to do this is to use dynamic_cast, and check for nullptr:

virtual bool IState::Equals(Object^ o) override {
    IState^ s = dynamic_cast<IState^>(o);
    if (s != nullptr) {
        ...
    }
    return false;
}

C-style cast (avoid those BTW) that you have used will actually do a safe_cast, which throws InvalidCastException on failure, so you have to spell out dynamic_cast explicitly.