The original intention for this was to clean up some code which was calling a Select to get an Index value so that basic zebra striping of rows could be done. It return an IndexedType generic class of type T which has properties for the original object and the index value of it.

public static IEnumerable<IndexedType<T>> Index<T>(this IEnumerable<T> source)
{
	return source.Select((x, i) => new IndexedType<T>() { Item = x, Index = i });
}

And the class returned:

public class IndexedType<T>
{
	public T Item { get; set; }
	public int Index { get; set; }
}

This could be extended to include values like if the index value is even, N-Indexed values, etc but I leave that up to the imagination of the programmer.