Cycle operator

cycle.cs

public static IEnumerable<T> Cycle<T>(this IEnumerable<T> collection, bool forceToList = false)
{
    var list = collection as IList<T>;

    if (list != null)
    {
        return CycleList(list);
    }
    
    return forceToList
        ? CycleList(collection.ToList())
        : CycleEnumerable(collection);
}

private static IEnumerable<T> CycleList<T>(IList<T> list)
{
    var counter = 0;
    var length = list.Count;

    if (length == 0)
        yield break;

    while (true)
    {
        yield return list[counter];
        counter = (counter + 1) % length;
    }
}

private static IEnumerable<T> CycleEnumerable<T>(IEnumerable<T> collection)
{
    var iter = collection.GetEnumerator();

    if (!iter.MoveNext())
        yield break;

    while (true)
    {
        do
        {
            yield return iter.Current;
        }
        while (iter.MoveNext());

        iter.Reset();
    }
}