trait User {   type Id }  final class MyUser extends User {   def sayHi = println("Hi!")      def sayBye(id: Id) = println("Bye!") }  (new MyUser).sayHi  I have an abstract type Id which is not initialized. When I try to run this code I have no messages telling me that ID is not initialized.  I have an error when try to invoke the method utilizing the type, which shows the error  (new MyUser).sayBye  Is that expected behavior even class is final?  As for me it should fail on compilation by seein...