Downcasting shared pointer to derived class with additional functionality - is this safe?

Question

Consider the following outline:

class Base { /* ... */ };

class Derived : public Base
{
public:
    void AdditionalFunctionality(int i){ /* ... */ }
};

typedef         


        

Answer 1

If the container should never have base objects in it (I can't tell from the question but that's implied by your edit) then you should make the container hold derived objects instead, and then you have automatic access to the additional function.

If the container can have both types of objects, then it seems that you want to be able to treat all the objects as the base class within that container. In this case you almost certainly want to use polymorphism to do the right thing: Have a virtual interface that basically says "Do this work" and the parent version may do nothing at all. Then the child version of the method implements the additional functionality you need.

I think you may have a code smell that your objects are less related than you think. Are you inheriting to reuse, or to allow substitution? You may also want to reconsider what your public interface looks like.

All that said, should you decide to continue with your current design (which I would at least strongly review) I think your downcasting should be safe as long as you check the result of the dynamic cast for non-null before using it.