Question

So suppose I have a tree class like this in c++

class Node{
    void addChild(Node*);
    /*obvious stuff*/
    protected:
        Node* parent;
        vector<Node*> children
}

class specialNode : public Node{
    void addChild(specialNode*);
    /*obvious stuff*/
    /*special stuff*/
}

Now whenever I access the children in specialTree, I obviously get Node*, not specialNode*.

But this specialNode* has member variables and functions that Node doesn’t have.

I can force specialNode to only have take specialNode as children and otherwise break in compile time,
but I still get Node* when accessing children/parent, and I have to cast it whenever I want to use special functions, even in specialNode functions.

Is there any clever, or just any better way to go about this?
Other than literally casting every time?

Answer 1

If you only need SpecialNode objects in your tree (and just want to encapsulate all generic tree functionality in Node) you can make Node a so called “mix-in” class like

template <class N>
class Node : public N {
public:
  void addChild(Node<N>*);
protected:
  Node<N>* parent;
  vector<Node<N>*> children;
};

class SpecialNodeBase {
  // Here comes all "special" data/methods for your "special" tree
};

typedef Node<SpecialNodeBase> SpecialNode;

After that you can construct a tree of SpecialNode objects and use all methods from SpecialNodeBase as well as additional tree-managing functions from Node