I have base-class Base from which is derived Derived1, Derived2 and Derived3.
I have constructed an instance for one of the the derived classes which I store as Base* a. I now need to make a deep copy of the object which I will store as Base* b.
As far as I know, the normal way of copying a class is to use copy constructors and to overload operator=. However since I don't know whether a is of type Derived1, Derived2 or Derived3, I cannot think of a way of using either the copy constructor or operator=. The only way I can think of to cleanly make this work is to implement something like:
class Base
{
public:
virtual Base* Clone() = 0;
};
and the implement Clone in in the derived class as in:
class Derivedn : public Base
{
public:
Base* Clone()
{
Derived1* ret = new Derived1;
copy all the data members
}
};
Java tends to use Clone quite a bit is there more of a C++ way of doing this?
Answer
This is still how we do stuff in C++ for polymorphic classes, but you don't need to do the explicit copy of members if you create a copy constructor (possibly implicit or private) for your objects.
class Base
{
public:
virtual Base* Clone() = 0;
};
class Derivedn : public Base
{
public:
//This is OK, its called covariant return type.
Derivedn* Clone()
{
return new Derivedn(*this);
}
private:
Derivedn(const Derivedn) : ... {}
};