[Lukas Klein]

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Thank you. I had to look up covariant return types, in case someone else stumbles across this, here is a example:

This works:

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

class Derived : public Base {
public:
    Derived* clone() const override {
        return new Derived(*this);
    }
};

int main() {
    Base* b = new Derived();
    Base* b_clone = b->clone();

    delete b;
    delete b_clone;
    return 0;
}

and this does not work:

class Base {
public:
    virtual std::unique_ptr<Base> clone() const {
        return std::make_unique<Base>(*this);
    }
    virtual ~Base() = default;
};

class Derived : public Base {
public:
    std::unique_ptr<Derived> clone() const override {
        return std::make_unique<Derived>(*this);
    }
};

int main() {
    std::unique_ptr<Base> b = std::make_unique<Derived>();
    std::unique_ptr<Base> b_clone = b->clone();
    return 0;
}

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