Food for thoughts -- polymorphisms in C++

[karthick88]

Just a famous interview question.. What are the different ways you could iplemet polymorphism in c++??


All i know is
1. Through Interfaces
2. Templates

To a certain extent function overloading

Anything else that comes to ur mind guys??

[Galik]

Through function pointers.

[karthick88]

Anything else guys???

[helios]

Unions. Generic pointers.

EDIT: Are you sure the question isn't "how would you implement polymorphism in C"?

[karthick88]

Well, Could be.. but just thinking about all the ways to exploit polymorphism in C++...

How is that you could implement polymorphism with unions??

What are generic pointerS?? ex please..

[helios]

http://www.google.com/search?q=generic+pointer

[Galik]

I think we're really discussing how polymorphism the 'general concept' can be achieved using C++ rather than the just the specific 'polymorphic' language facilities designed into C++.

[karthick88]

Ok.. So how do we exploit polymorphism using unions??

Galik.. We could even discuss from that side.. Y don you post what you think?

[everid]

Ok.. So how do we exploit polymorphism using unions??

#include <iostream>
#include <typeinfo>
using namespace std;
class Base{
public:
  virtual void see() const{
    cout<<typeid(pointee.d).name()<<endl;
  }
protected:
  union {
    int* d;
    char* p;
  }pointee;
};

class Der:public Base{
public:
  virtual void see() const{
    cout<<typeid(pointee.p).name()<<endl;
  }
};

int main(int argc, char* argv[]){
  const Base& b=Der();
  b.see();
}

I came up with this snip code to show the concept of using union with polymorphism. there could be practical application by using union because it saves space.

[jsmith]

Ok.. So how do we exploit polymorphism using unions??

The real question is not how, but why. Why exactly would I want to use a union
to implement polymorphism when the language intrinsically supports it with inheritance
and virtual functions.

If asked how to exploit polymorphism using unions during a job interview, the
right answer is to walk out and find a different job. The concept is stupid.

[karthick88]

I guess helios has become busy..!! Hope he ll give us the explanation.. maybe he had someother idea in his mind when he cited unions as a tool for polymorphism...

@everid
Thanks for your idea. But again here we use virtual functions as the tool of polymorphism and we use unions for efficiency..