Polymorphic copy-constructor with type conversion

Question

I need to copy-construct an object simultaneously changing it\'s type to another class being a member of the same class-hierarchy. I\'ve read about polymorphic copy-constructors

Answer 1

If you only have 2 child classes, then the easiest way is to create a conversion constructor:

class Child2: public Base
{
public: 
    Child2(Child1 const& child)
    {
            p_int = new int (*child.p_int);
            a = child.a + 1;        
    }
}; 

c2 = new Child2(*c1); 

If you have several Child classes, and you need to create a Child2 from any of them, then you could do something like this:

class Base
{
public: 
    void CopyFrom(Base* base)
    {
            p_int = new int (*base.p_int);
            a = base.a + 1;     
    }
}; 

class ChildX: public Base
{
public: 
    static ChildX* CreateFrom(Base* base)
    {
        ChildX ch = new ChildX(); 
        ch->CopyFrom(base); 
        return ch; 
    }
}; 

c2 = Child2::CreateFrom(c1);