C#'s equivalent of Java's <? extends Base> in generics

Question

In Java, I can do the following: (assume Subclass extends Base):

ArrayList<? extends Base> aList = new ArrayList<Subclass>(); 

What is the equivalent in C# .NET? There is no ? extends keyword apparently and this does not work:

List<Base> aList = new List<Subclass>(); 

Answer 1

Actually there is an Equivalent(sort of), the where keyword. I don't know how "close" it is. I had a function I needed to do something similar for.

I found an msdn page about it.

I don't know if you can do this inline for a variable, but for a class you can do:
public class MyArray<T> where T: someBaseClass
or for a function
public T getArrayList<T>(ArrayList<T> arr) where T: someBaseClass

I didn't see it on the page but using the where keyword it might be possible for a variable.

Answer 2

Look into Covariance and Contravariance introduced with .Net 4.0. But it only works with interfaces right now.

Example:

IEnumerable<Base> list = new List<SubClass>();