IndexedEnumerator.cs

    public interface IIndexedEnumerator<T> : IEnumerator<T>
    {
        int Index
        {
            get;
        }

        bool IsOdd
        {
            get;
        }
         
    } 

    public static class IndexedEnumerationExtensions
    {
        public static IIndexedEnumerator<T> GetIndexedEnumerator<T>(this IEnumerable<T> collection)
        {
            return new IndexedEnumerator<T>(collection.ToArray());
        }

        public class IndexedEnumerator<T> : IIndexedEnumerator<T>
        { 

            private T[] _array;

            internal IndexedEnumerator(T[] array)
            {
                _array = array;
                this.Reset();
            }

            public bool IsOdd => (this.Index & 1) == 1;

            public int Index
            {
                get;
                private set;
            }

            public T Current => this._array[this.Index];

            public void Dispose()
            {
                _array = null;
            }

            public bool MoveNext()
            {
                this.Index++;
                return this.Index < this._array.Length;
            }

            public void Reset()
            {
                this.Index = -1;
            }

            object IEnumerator.Current => this.Current;
        }
    }