The best way to get a count of IEnumerable

Question

Whats the best/easiest way to obtain a count of items within an IEnumerable collection without enumerating over all of the items in the collection?

Possible with LIN

Answer 1

There's also IList or ICollection, if you want to use a construct that is still somewhat flexible, but also has the feature you require. They both imply IEnumerable.