Indexable interface

Question

What C# interface should be used if I only want to be able to index into instances of a type? I don't need (or want) the ability to add/remove/edit elements. Enumeration is okay. Does this require a custom IIndexable type?

In this case IList is overkill because it forces implementation of members I don't want to have.

Answer 1

As of .Net 4.5 the (arguably) right way is now to use IReadOnlyList<T>, which derives from IReadOnlyCollection<T>, which derives from IEnumerable<T>

• IReadOnlyList<T> gives you the indexer
• IReadOnlyCollection<T> gives you the collection Count property.
• IEnumerable<T> gives you the collection Enumerator.

Its about as light as you can make it.

Core classes that directly implement IReadOnlyList:

• List<T>
• Collection<T>
• ReadOnlyCollection<T>
• ArraySegment<T>
• T[]