There is no harm using LINQ's Count() with a List

1

It was my understanding and I think others that you should never call LINQ’s Count() extension method on a List because it doesn’t use List’s Count property, resulting in a performance of O(N) instead of O(1).

That’s wrong. LINQ checks if the type is of ICollection, which has the Count property, and returns it if so.

2

Good to know. I’ve actually always used LINQ’s Count() with lists, and I just assumed there was something in there to give it good performance.

3

I remember years ago looking up if that was the case and I thought it was determined that it wasn’t smart.