IEnumerable as return type

Question

Is there a problem with using IEnumerable as a return type? FxCop complains about returning List (it advises returning Coll

Answer 1

About your principle: "accept the least you can, but return the maximum".

The key to managing the complexity of a large program is a technique called information hiding. If your method works by building a List, it's not often necessary to reveal this fact by returning that type. If you do, then your callers may modify the list they get back. This removes your ability to do caching, or lazy iteration with yield return.

So a better principle is for a function to follow is: "reveal as little as possible about how you work".