Base class constraint on generic class specifying the class itself

Question

Yesterday, I was explaining C#\'s generic constraints to my friends. When demonstrating the where T : CLASSNAME constraint, I whipped up something like this:

Answer 1

This approach is widely used in Trees and other Graph-like structures. Here you say to compiler, that T has API of UnusableClass. That said, you can implement TreeNode as follows:

public class TreeNode
    where T:TreeNode
{
    public T This { get { return this as T;} }

    public T Parent { get; set; }

    public List Childrens { get; set; }

    public virtual void AddChild(T child)
    {
        Childrens.Add(child);
        child.Parent = This;
    }

    public virtual void SetParent(T parent)
    {
        parent.Childrens.Add(This);
        Parent = parent;
    }
}

And then use it like this:

public class BinaryTree:TreeNode
{
}