They added Covariance and Contravariance of generic type parameters in 4. http://msdn.microsoft.com/en-us/library/dd799517%28v=vs.110%29.aspx http://msdn.micros

They added Covariance and Contravariance of generic type parameters in 4. http://msdn.microsoft.com/en-us/library/dd799517%28v=vs.110%29.aspx http://msdn.microsoft.com/en-us/library/dd799517%28v=vs.110%...