Why its better (Return IList Instead of return List)? [duplicate]

Question

Possible Duplicate:
C# - List<T> or IList<T>

When I return a list from my method I can do in 2 way. As a List

Private List<datatype> MethodName()
{
    Return List
}

As a IList

Private IList<datatype> MethodName()
{
    Return IList
}

As I heard we should return it as a IList. Is anyone can explain whys that?

Answer 1

You can't return an IList - you need to return an implementation of that interface (i.e. a List). Of course returning a 'List' will satisfy your method declaration of returning a IList because List implements IList.

Generally best practice is to accept parameters of the most generic type and to return the most specific. However, conventionally programmers tend to not want to tie themselves to the List implementation and normally return the IList interface. You could be returning an IEnumerable if you don't want callers to modify the array (call the .AsReadOnly() extension method on your IList).