I have a need to clone a derived class given only a reference or pointer to the base class. The following code does the job, but doesn't seem elegant, because I'm putting boilerplate code into many derived classes C, D, E that are siblings of B (not shown) that just calls the default copy constructor of each. Isn't that what the default copy constructor is for, if only it could be virtual?
Is there a better way?
Making a virtual assignment operator would be wrong, as I don't want C to assign to B, B to D, etc, just clone B, C, D or E.
#include <iostream>
using namespace std;
class A {
public:
virtual ~A() {}
virtual A* clone()=0;
};
class B : public A {
int i;
public:
virtual A* clone() {
cout << "cloned B" << endl;
return new B(*this);
}
virtual ~B() { cout << "destroyed b" << endl; }
};
int main() {
A* a = new B();
A* aa = a->clone();
delete a;
delete aa;
return 0;
}
You could always stick all the cloning logic into its own class in the middle of the hierarchy:
template <class Derived, class Base>
class CloneCRTP : public Base {
public:
Derived* clone() const override {
return new Derived(static_cast<Derived const&>(*this));
}
};
And then:
class B : public CloneCRTP<B, A>
{
int i;
public:
virtual ~B() { cout << "destroyed b" << endl; }
};
No more boilerplate.