Return an empty IEnumerator

Question

I have an interface that, among other things, implements a "public IEnumerator GetEnumerator()" method, so I can use the interface in a foreach statement.

I implement this interface in several classes and in one of them, I want to return an empty IEnumerator. Right now I do this the following way:

public IEnumerator GetEnumerator()
{
    ArrayList arr = new ArrayList();
    return arr.GetEnumerator();
}

However I consider this an ugly hack, and I can't help but think that there is a better way of returning an empty IEnumerator. Is there?

Answer 1

I wrote it like this:

public IEnumerator<T> GetEnumerator()
{
    return this.source?.GetEnumerator() ??
            Enumerable.Empty<T>().GetEnumerator();
}

Answer 2

There is an extra function in the framework:

public static class Enumerable
{
    public static IEnumerable<TResult> Empty<TResult>();
}

you can write

var NullEnumerable = Enumerable.Empty<int>();

Answer 3

Found this question looking for the simplest way to get an empty enumerator. After seeing the answer comparing performance I decided to use the empty enumerator class solution, but mine is more compact than the other examples, and is a generic type, and also provides a default instance so you don't have to create new instances all the time, which should even further improve performance.

class EmptyEnumerator<T> : IEnumerator<T>
{
   public readonly static EmptyEnumerator<T> value = new EmptyEnumerator<T>();
   public T Current => throw new InvalidOperationException();
   object IEnumerator.Current => throw new InvalidOperationException();
   public void Dispose() { }
   public bool MoveNext() => false;
   public void Reset() { }
}