The non-generic type 'System.Collections.IEnumerable' cannot be used with type arguments

Question

using System.Collections.Generic;

public sealed class LoLQueue<T> where T: class
{
    private SingleLinkNode<T> mHe;
    private SingleLinkNode<T> mTa;

    public LoLQueue()
    {
        this.mHe = new SingleLinkNode<T>();
        this.mTa = this.mHe;
    }
}

Error:

The non-generic type 'LoLQueue<T>.SingleLinkNode' cannot be used with type arguments

Why do i get this?

What is your definition of SingleLinkNode? – Matthew Abbott Aug 03 '11 at 18:43 — Matthew Abbott, Aug 03 '11 at 18:43

score 30 · Answer 1 · answered Aug 03 '11 at 18:40

30

If you want to use IEnumerable<T>, as your post's title suggests, you need to include using System.Collections.Generic;.

As for the SingleLinkNode class, I don't know where you got it, it's not part of the .NET framework that I can see. I'd guess that it isn't implemented using generics, and you'll need to add a bunch of casts from object to T everywhere.

answered Aug 03 '11 at 18:40

David Yaw

27,383
4
60
93

4

He already has that listed on the **first line** of his code. – WEFX Aug 03 '11 at 18:43
True, but considering the title of this question is "The non-generic type System.Collections.IEnumerable", I assumed that something changed in the copy-paste of code. – David Yaw Aug 03 '11 at 18:46
This solved the problem for me, but I don't know why I only needed this on one server and not the others that I put it on. Is there some defaults that are set at a server level somewhere? – Graham May 22 '19 at 14:31

dlev · Accepted Answer · 2011-08-03T18:48:26.403

I'm pretty sure you haven't defined your SingleLinkNode class as having a generic type parameter. As such, an attempt to declare it with one is failing.

The error message suggests that SingleLinkNode is a nested class, so I suspect what may be happening is that you are declaring members of SingleLinkNode of type T, without actually declaring T as a generic parameter for SingleLinkNode. You still need to do this if you want SingleLinkNode to be generic, but if not, then you can simply use the class as SingleLinkNode rather than SingleLinkNode<T>.

Example of what I mean:

public class Generic<T> where T : class
{
    private class Node
    {
        public T data; // T will be of the type use to construct Generic<T>
    }

    private Node myNode;  // No need for Node<T>
}

If you do want your nested class to be generic, then this will work:

public class Generic<T> where T : class
{
    private class Node<U>
    {
        public U data; // U can be anything
    }

    private Node<T> myNode;  // U will be of type T
}

score 2 · Answer 3 · answered Aug 03 '11 at 18:46

This compiles for me:

public sealed class SingleLinkNode<T>
{

}

public sealed class LoLQueue<T> where T : class
{
    private SingleLinkNode<T> mHe;
    private SingleLinkNode<T> mTa;

    public LoLQueue()
    {
        this.mHe = new SingleLinkNode<T>();
        this.mTa = this.mHe;
    }
}

You'll need to post your SingleLinkNode class for further answers...

John

The non-generic type 'System.Collections.IEnumerable' cannot be used with type arguments

3 Answers3