Question

I have a function that takes a pointer to a superclass and performs operations on it. However, at some point, the function must make a deep copy of the inputted object. Is there any way I can perform such a copy?

It occurred to me to make the function a template function and simply have the user pass the type, but I hold out hope that C++ offers a more elegant solution.

Answer 1

SpaceCowboy proposes the idiomatic clone method, but overlooked 3 crucial details:

class Super
{
public:
  virtual Super* clone() const { return new Super(*this); }
};

class Child: public Super
{
public:
  virtual Child* clone() const { return new Child(*this); }
};

1. clone is a const method
2. clone returns a pointer to the current class, not the base class
3. clone returns a copy of the current object

The 2nd is very important, because it allows use to benefit from the fact that sometimes you have more type information than just a Super*.

Also, I usually prefer clone to provide a copy, and not merely a new object of the same type. Otherwise you’re using an Exemplar pattern to build new objects, but you’re not cloning proper and the name is misleading.