Which interface to choose?

Question

Which data collection interface is preferable for the system? By system, I mean repositories, services, etc. So I need to select IEnumerable, ICollection, IList, or maybe even List.

I suppose it would theoretically be better to use IEnumerable. But this is less convenient to use: for example, I should use the GetElementAt method instead of the indexer.

My current choice is IList, but I doubt this decision.

Answer 1

In fact, it all depends on what type of access you want to allow for consumers of your repositories, services, etc.

If you only want consumers to read the collection, use IEnumerable<T> (write methods are not available).

If you want consumers to add directly to the collection, the methods in ICollection<T> will give them that.

In general, I try to expand collections as IEnumerable<T> as often as possible. When users want to add something to the collection, they should call a separate method, and not directly write to the collection. This gives you the ability to verify your entry, perform other checks, etc.

Answer 2

If you want to allow indexer access, you must use IList<T> . The general rule is to use the least specific type, which still meets all usage requirements. And in your case, it looks like a list. (and, of course, IList<T> less specific than List<T> )