我该如何实例化此类？

Question

Consider this declaration with generics:

public class BaseNode<TNode> where TNode : BaseNode<TNode>
{
    public class Node : BaseNode<Node>
    {
        public Node() { }
    }
}

Is there a way to create an instance of class Node from outside the base class? I have used this pattern before, but always leaving the derived classes outside of the base class.

How do you write the following without a compiler error?

var obj = new BaseNode<Node>.Node(); 
// error CS0246: The type or namespace name 'Node' could not be found

Have I created an un-instantiable class? Can it be initialized via reflection?

Answer 1

You can instantiate that monster. All you have to do is create your own class that inherits from Node :

public class MyNode : BaseNode<MyNode>.Node
{
}

Then you can instantiate it like this:

BaseNode<MyNode> obj = new BaseNode<MyNode>();

Why you would want to do this, though, is a different matter entirely...

Answer 2

Add a static factory method:

public static Node Create<T>()
{
    return // your new Node
}

And call it thusly:

var foo = BaseNode<Node>.Create<Node>();