C++ elegantly clone derived class by calling base class

Question

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

Answer 1

To achieve clone that works as with covariant return type, there is a need for some more complicated CRTP:

class Shape {
    // virtual
    virtual Shape* do_clone() const = 0;
public:
    virtual ~Shape() {}
    // non-virtual
    Shape* clone() const {
        return do_clone();
    }
    // ...
};

template 
class CloneCRTP : public Base {
    // virtual
    Shape* do_clone() const override {
        return new Derived(static_cast(*this));
    }
public:
    // non-virtual
    Derived* clone() const {
        return static_cast(do_clone());
    }    
};

Usage:

class Rectangle: public CloneCRTP { /*...*/ };    
class Triangle: public CloneCRTP { /*...*/ };

int main() {
    Rectangle* r1 = new Rectangle{};

    // getting the proper type from clone:
    Rectangle* rcopy = r1->clone();

    delete rcopy;
    delete r1;

    Triangle t1{};

    // getting the proper type from clone:
    Triangle* tcopy = t1.clone();

    delete tcopy;
}

Code: http://coliru.stacked-crooked.com/a/d8781deee5f7f6ea