class MyClass {
public:
void set(Base* var) {
m_var = new Base(*var));
}
private:
Base* m_var;
};
Maintaining polymorphism of copies
Author
Okay, am I being really stupid here or what? I have a class that stores a pointer or reference to a base class. This class has a setter method for this member variable, which accepts a pointer or reference to a base class. I want this method to make a copy of the pointed-to object, and store a pointer to the copy, in order to be able to cast to derived types later. Can I do something like below, or will the object be sliced? I'm fairly sure it will, so what should I be doing instead? I know this is very simple, but my brain's gone numb.
Is there a reason you're trying to implement your own inheritance? Why not just derive MyClass from Base? Or is this not really supposed to be a base class?
No, that won't work. It'll create a new Base object that copies the Base properties of the passed object. It will not create a derived class instance.
The common method for doing things like this is to implement a pure virtual clone method in the Base class interface:
As a side note, generally if you are upcasting from base to derived there is something wrong with your architecture.
-me
The common method for doing things like this is to implement a pure virtual clone method in the Base class interface:
class Base{public: virtual Base *clone() = 0;};class Derived : public Base{public: virtual Base *clone();}Base *Derived::clone(){ return new Derived(this);}As a side note, generally if you are upcasting from base to derived there is something wrong with your architecture.
-me
Palidine: your approach is the correct one, but why is the base version of the clone function pure virtual?
Author
Paladine: Thanks, that's perfect. I've always wondered what these mysterious 'clone()' methods I've seen were for :)
Also, I'm well aware that the architecture I'm using is rubbish, it's just too late in the project to change it! "if it works..." and all that.
Also, I'm well aware that the architecture I'm using is rubbish, it's just too late in the project to change it! "if it works..." and all that.
Author
Ooh, lightning quick question: do you mean "return new Derived(*this);" - '*this' instead of 'this'?
Quote:Original post by hymerman
Ooh, lightning quick question: do you mean "return new Derived(*this);" - '*this' instead of 'this'?
Yes.
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
