Delegation pattern

http://en.wikipedia.org/wiki/Delegation_pattern

 

#include <iostream>
 using namespace std;
 
 class I {
   public:
     virtual void f() = 0;
     virtual void g() = 0;
     virtual ~I() {}
 };
 
 class A : public I {
   public:
     void f() { cout << "A: doing f()" << endl; }
     void g() { cout << "A: doing g()" << endl; }
     ~A() { cout << "A: cleaning up." << endl; }
 };
 
 class B : public I {
   public:
     void f() { cout << "B: doing f()" << endl; }
     void g() { cout << "B: doing g()" << endl; }
     ~B() { cout << "B: cleaning up." << endl; }
 };
 
 class C : public I {
   public:
     // construction/destruction
     C() : i( new A() ) { }
     virtual ~C() { delete i; }
 
   private:
     // delegation
     I* i;
 
   public:
     void f() { i->f(); }
     void g() { i->g(); }
 
     // normal attributes
     void toA() { delete i; i = new A(); }
     void toB() { delete i; i = new B(); }
 };
 
 int main() {
     C* c = new C();
 
     c->f();
     c->g();
     c->toB();
     c->f();
     c->g();

  return 1;
 }