Clarification via EricGu...having an Everett assembly reference a Whidbey assembly is not a supported scenario, plus generic metadata will cause weird things to happen.  
Thanks Eric :) 

Someone sent a question recently to an internal alias so I thought I would share. The question was what will happen when a C# V1 component consumes a C# V2 component that exposes a generic class.  First some background information, there are two types of compatibility, backward compatibility and forward compatibility. 

  • Backward compatibility refers to a future version of a product, like Whidbey, supporting already existing functionality like something found in .
  • Forward compatibility refers to an older product, like Everett, being able to support a new feature like generics.

As you can imagine, it's easier to add backward compatibility since it is a known thing.  Designing for forward compatibility can be more difficult as it is an unknown thing.  The goal of C# Whidbey is geared more towards backward compatibility so that if you write a component today for version 1.x, your component will "just work" in C# Whidbey. 

I decided to test what forward compatibility will work with the current Tech preview for a VS Whidbey component to be used in VS 2003. To test forward compatibility, I created a simple generic class with two static methods.  The first method returns a generic collection, the second returns a non-generic collection.

V2 Code

public class GenericClass



     public static List<int> ReturnGeneric()


           List<int> l = new List<int>();


           return l;



     public static ArrayList ReturnNonGeneric()


           ArrayList ar = new ArrayList();


           return ar;



I added a reference to the GenericClass in VS 2003. Using IntelliSense, the only method that is available to execute is GenericClass.ReturnNonGeneric() since VS 2003 doesn't understand a non-generic type.  Since VS 2003 doesn't understand generic types it can't call the ReturnGeneric() method.