Is it possible to clone a polymorphic object without manually adding overridden clone method into each derived class in C++?

Question

The typical pattern when you want to copy a polymorphic class is adding a virtual clone method and implement it in each derived class like this:

Base* Derive         


        

Answer 1

You can use this generic CRTP code

template 
struct Clonable : Base {
    virtual Base* do_clone() {
        return new Derived(*static_cast(this));
    }
    Derived* clone() { // not virtual
        return static_cast(do_clone());
    }

    using Base::Base;
};

struct empty {};
struct A : Clonable {};
struct B : Clonable {};

It can be generalised to smart pointers and multiple bases if desired.