Returning 'IList' vs 'ICollection' vs 'Collection'

c# .net generics collections
Rocky Singh picture Rocky Singh · Mar 24, 2012 · Viewed 63k times · Source

I am confused about which collection type that I should return from my public API methods and properties.

The collections that I have in mind are IList, ICollection and Collection.

Is returning one of these types always preferred over the others, or does it depend on the specific situation?

Answer

cordialgerm picture cordialgerm · Mar 24, 2012

ICollection<T> is an interface that exposes collection semantics such as Add(), Remove(), and Count.

Collection<T> is a concrete implementation of the ICollection<T> interface.

IList<T> is essentially an ICollection<T> with random order-based access.

In this case you should decide whether or not your results require list semantics such as order based indexing (then use IList<T>) or whether you just need to return an unordered "bag" of results (then use ICollection<T>).

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