Generalized structural type conformance in Scala

Question

I\'m interested in the problem of conforming a specific type to a more general structural type. Consider the following examples:

trait Sup

trait Sub extend         


        

Answer 1

One concern is that when you read this code:

self: { def copy(version: Int): T }

you do not expect the name of the parameter to be significant, as it would have to be in this example:

case class Robot(number: Int, override val version: Int)
  extends Versionable[Robot]

EDIT: On another note, regarding the lack of parameter contravariance for methods, you can do:

type General = { val contra: (Sub => Unit) }
class B { val contra = ((o:Sup) => println(o)) }
var b:General = new B