Question

I have 3 class which derived from each other:

class Basic{
...
}

class Extended : public Basic{
...
}

class Full : public Extended{
...
}

I have a template class which holds 5-5 from this classes:

template <class T>
    class group{
    public:
             ...
    private:
        T one, two, three, four, five;
    };

group<Basic> basicGroup;
group<Extended> extendedGroup;
group<Full> fullGroup;

Can I easily cast for example fullGroup to basicGroup or extendedGroup to basicGroup? (I just want to cast upward)

Answer 1

A solution would be to create a kind of view-class that can wrap a group, and exposes the individual objects as base-class instances:

template <class T>
class group{
public:
    const T & getOne() { return one; }
private:
    T one, two, three, four, five;
};

template <class T, U>
class group_view {
public:
    group_view(group<T> & inner) : innerGroup(inner) {}

    const U & getOne() { return dynamic_cast< const U &>(one); }
private:
    group<T> & innerGroup;
};

You could use it like this:

group<Full> fullGroup;
group_view<Full, Extended> extendedGroupView(fullGroup);

If you extract the public interface of group into an abstract base class, you can even use group_views polymorphically.