LINQ meta operator. Wraps each element in a meta object also containing the index in the sequence and whether the element is first and if it is last in the sequence.

gistfile1.cs

    public class MetaElement<T>
    {
        public MetaElement(T value, bool isLast, bool isFirst, int index)
        {
            this.Value = value;
            this.IsLast = isLast;
            this.IsFirst = isFirst;
            this.Index = index;
        }
        public int Index { get; private set; }
        public bool IsFirst { get; private set; }
        public bool IsLast { get; private set; }
        public T Value { get; private set; }
    }

    public static class Ex
    {
        public static IEnumerable<MetaElement<T>> Meta<T>(this IEnumerable<T> source)
        {
            using (var etor = source.GetEnumerator())
            {
                if (false == etor.MoveNext())
                    yield break;

                var isFirst = true;
                var lastValue = etor.Current;
                int index = 0;

                while (etor.MoveNext())
                { 
                    yield return new MetaElement<T>(lastValue, isLast: false, isFirst: isFirst, index: index);
                    isFirst = false;
                    lastValue = etor.Current;
                    index++;
                }

                yield return new MetaElement<T>(lastValue, isLast: true, isFirst: isFirst, index: index);
            }
        }
    }