Stepping Up To C++

Listing 1 A polymorphic hierarchy of shapes with a clone function

class shape
   {
public:
   virtual shape *clone() const = 0;
   ...
   };

class circle : public shape
   {
public:
   shape *clone() const;
   ...
   };

shape *circle::clone() const
   {
   return new circle(*this);
   }

class rectangle : public shape
   {
public:
   shape *clone() const;
   ...
   };

shape *rectangle::clone() const
   {
   return new rectangle(*this);
   }