How to Deep Copy Polymorphic Objects in C Using Clone and Covariant Return Types?

Copying Polymorphic Objects in C : Understanding Clone and Copy Constructors

In C , inheritance allows creating polymorphic classes, where objects of derived classes can be stored as their base class pointers. When dealing with such objects, the need often arises to make a deep copy of them. While conventional copy constructors and operator= overloading may not suffice, a specific approach is required.

The idea of using a Clone() method, as demonstrated in the question, is a common technique in C . This abstract method is declared in the base class and implemented in derived classes to create a deep copy of their specific type.

However, there is a more C -specific approach that simplifies this process. By employing the concept of covariant return types, derived classes can return pointers to themselves when overriding the Clone() method. Additionally, a private or implicit copy constructor in the derived class can handle the actual data member copying.

Here's an example:

class Base
{
public:
  virtual Base* Clone() = 0;
};

class Derivedn : public Base
{
public:
  // Covariant return type allows returning a pointer to a derived class.
  Derivedn* Clone() 
  {
    return new Derivedn(*this);
  }
private:
  Derivedn(const Derivedn&) : ... {}
};

In this approach, the Clone() method in Derivedn returns a pointer to a new object of the same type as itself. The private copy constructor in Derivedn takes care of copying data members, ensuring a deep copy.

This technique offers a clean and concise way to create copies of polymorphic objects in C while adhering to its object-oriented principles.

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