Return all enumerables with yield return at once; without looping through

Question

I have the following function to get validation errors for a card. My question relates to dealing with GetErrors. Both methods have the same return type IEnumerable&

Answer 1

Yes it is possible to return all errors at once. Just return a List or ReadOnlyCollection.

By returning an IEnumerable you're returning a sequence of something. On the surface that may seem identical to returning the collection, but there are a number of difference, you should keep in mind.

Collections

• The caller can be sure that both the collection and all the items will exist when the collection is returned. If the collection must be created per call, returning a collection is a really bad idea.
• Most collections can be modified when returned.
• The collection is of finite size.

Sequences

• Can be enumerated - and that is pretty much all we can say for sure.
• A returned sequence itself cannot be modified.
• Each element may be created as part of running through the sequence (i.e. returning IEnumerable allows for lazy evaluation, returning List does not).
• A sequence may be infinite and thus leave it to the caller to decide how many elements should be returned.