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

I think your own guidance is great -- if you are able to be more specific about what you're returning without a performance hit (you don't have to e.g. build a List out of your result), do so. But if your function legitimately doesn't know what type it's going to find, like if in some situations you'll be working with a List and in some with an Array, etc., then returning IEnumerable is the "best" you can do. Think of it as the "greatest common multiple" of everything you might want to return.