Node class model

Question

I have made a base class Node with methods for adding and removing children, handling parents and searching for ancestors, descendants etc. So far so good.

Now I want to make a derived type TreeNode : Node that benifits from all these Node-features but at the same time restricting children and parent to have the same TreeNode type. As it is now I still have Node as type for children and parent.

Can I somehow make the property and method argument types of the Node class change to match the type of the derived class without having to manually override or "new"?

class Node
{
  public TypeOfThisInstance Parent { get; }
}

class TreeNode : Node
{
}

TreeNode.Parent should now be a TreeNode and not a Node.

Why do you even want to do that? How is TreeNode different from Node? — svick
– svick, Commented Apr 22, 2012 at 14:00

Magnus · Accepted Answer · 2012-04-22 14:10:46Z

1

Using Generics:

public class BaseNode<T> where T : BaseNode<T>
{
  private T _parent;
  public T Parent { get { return _parent;} }
}
public class Node : BaseNode<Node>
{
} 
public class TreeNode : BaseNode<TreeNode>
{
}

edited Apr 22, 2012 at 14:10

answered Apr 22, 2012 at 13:53

Magnus

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3 Comments

svick Over a year ago

I think, the limitations of this approach should be pointed out: you can make class Node : BaseNode<int> or class TreeNode : BaseNode<Node>. It doesn't make much sense, but you can do it. You can avoid some (but not all) of those problems by using generic constraints.

Magnus Over a year ago

Yep, @svick is correct. You can add a constraint on the BaseNode class like: where T : BaseNode<T>

Andreas Zita Over a year ago

Thanks. I'm pretty sure I have tried this before and only got StackOverflowExceptions ... strange... It seem to work fine now!

Amir Ismail · Accepted Answer · 2012-04-22 13:54:58Z

0

I think you need to build the composite design pattern. It is all about creating tree-like structures where the leaves in the structure can be treated in the same way as the branches(which are substructures that can contain multiple leaves, as well as other branches). The idea here is that, to make life easier, you should be able to treat the leaves and compositions of leaves in a tree structure the same.

answered Apr 22, 2012 at 13:54

Amir Ismail

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