How do I copy an object using a pointer?

Question

I am learning C++ and our teacher ask us to use a copy function with a pointer. He gave us a similar code to this one but I can't figure out how to use the copy function:

class Animal
{
public:
    ...
    virtual Animal* copy() const =0;
}


class Dog : public Animal
{
public:
    ...
    virtual Animal* copy() const;
}


Animal* Dog::copy() const
{
    return new Dog(*this);
}


int main(){
Dog husky (…);
//Labrador = copy() of husky 
}

For example, what should I write to create a new objet (labrador) as a copy of an object (husky)?

Thanks

Answer 1

In this case, you don't actually need to use that copy() method at all, because you know that your husky object is a Dog and you want the copy to be another Dog. So you can just write

Dog labrador(husky)

to construct labrador as a copy of husky using its copy constructor.

The point of the copy() method is that sometimes you just have an Animal* and you don't actually know what concrete type of animal it points to, so you don't know what type of new animal to create. For example:

void example(Animal const *animal) {
    Animal *clonedAnimal = animal->copy();
}

The example function doesn't know what kind of Animal it's been given, but the animal object itself knows what it is, and the virtual function call lets that animal take care of copying itself. If animal points to a Dog instance, the Dog version of copy() will run and construct a Dog. If animal points to a Cat, the Cat version of the function will run and construct a new Cat.