How is Generic Covariance & Contra-variance Implemented in C# 4.0?

Question

I didn\'t attend PDC 2008, but I heard some news that C# 4.0 is announced to support Generic covariance and contra-variance. That is, List can be

Answer 1

Not that Jon hasn't already covered it, but here are some links to blogs and videos from Eric Lippert. He does a nice job of explaining it with examples.

https://blogs.msdn.microsoft.com/ericlippert/2007/10/16/covariance-and-contravariance-in-c-part-one/

The videos:

https://www.youtube.com/watch?v=3MQDrKbzvqU

https://www.youtube.com/watch?v=XRIadQaBYlI

https://www.youtube.com/watch?v=St9d2EDZfrg