Question

I’m trying to create a simple way to have my linkedlist act like a circular linked list in C#.

I have this code, and it does not want to show up as an extension method. Any idea why?

static class CircularLinkedList
{
    public static LinkedListNode<object> NextOrFirst(this LinkedListNode<object> current)
    {
        if (current.Next == null)
            return current.List.First;
        return current.Next;
    }

    public static LinkedListNode<object> PreviousOrLast(this LinkedListNode<object> current)
    {
        if (current.Previous == null)
            return current.List.Last;
        return current.Previous;
    }
}

Answer 1

This works fine for me in the following application:

class Program
{
    static void Main(string[] args)
    {
        LinkedListNode<object> node = new LinkedListNode<object>("Hello World");
        node.NextOrFirst();
    }
}

static class CircularLinkedList
{
    public static LinkedListNode<object> NextOrFirst(this LinkedListNode<object> current)
    {
        if (current.Next == null)
            return current.List.First;
        return current.Next;
    }

    public static LinkedListNode<object> PreviousOrLast(this LinkedListNode<object> current)
    {
        if (current.Previous == null)
            return current.List.Last;
        return current.Previous;
    }
}

Make sure that you are instantiating your LinkedListNode with the proper generic type , as using any other type (i.e. string) will not work. However, you can extend this to support any type of LinkedListNode by changing your code to the following:

class Program
{
    static void Main(string[] args)
    {
        LinkedListNode<string> node = new LinkedListNode<string>("Hello World");
        node.NextOrFirst<string>();

        LinkedListNode<int> node2 = new LinkedListNode<int>(3);
        node2.NextOrFirst<int>();
    }
}

static class CircularLinkedList
{
    public static LinkedListNode<T> NextOrFirst<T>(this LinkedListNode<T> current)
    {
        if (current.Next == null)
            return current.List.First;
        return current.Next;
    }

    public static LinkedListNode<T> PreviousOrLast<T>(this LinkedListNode<T> current)
    {
        if (current.Previous == null)
            return current.List.Last;
        return current.Previous;
    }
}