Question

In my program I have a Base class with many inherited classes. I need to store a list of these inherited objects (or any container). The only way I can think of to do this is by having a list of the Base class with some type enumeration and then down casting to the inherited type.

Having to constantly cast my objects seems like a heavy penalty for just trying to have my objects in some container.

Are there any other options? Is casting not as bad as it seems?

Thanks for the help!

Answer 1

Use polymorphism via virtual functions, that’s what they’re there for:

#include <algorithm>
#include <functional>
#include <iostream>
#include <list>

using namespace std;

class A {
public:
  virtual void print() {
    cout << "This is an A object" << endl;
  }
};

class B : public A {
public:
  virtual void print() {
    cout << "This is a B object" << endl;
  }
};

class C : public A {
public:
  virtual void print() {
    cout << "This is a C object" << endl;
  }
};

class D : public B {
  // empty
};

int main() {
  std::list<A*> objects;
  objects.push_back(new A());
  objects.push_back(new B());
  objects.push_back(new C());
  objects.push_back(new D());

  for_each(objects.begin(), objects.end(), mem_fun(&A::print));

  return 0;
}

// outputs:
// This is an A object
// This is a B object
// This is a C object
// This is a B object