Derived List to Base IEnumerable

Question

I have the following code that compiles in .NET Framework version 4.0 and above:

public abstract class MyBase { }
public class MyDerived : MyBase { }

public abs         


        

Answer 1

It's about covariance and contravariance of collections. Check the following link to get more information.

Starting with the .NET Framework 4, several generic interfaces have covariant type parameters; for example: IEnumerable, IEnumerator, IQueryable, and IGrouping. All the type parameters of these interfaces are covariant, so the type parameters are used only for the return types of the members.