Scala immutable objects and traits with val fields

Question

I would like to construct my domain model using immutable objects only. But I also want to use traits with val fields and move some functionality to traits. Please look at the f

Answer 1

Here's another solution that, like the OP's code, doesn't work. However, it may provide a simpler (and more generally useful) starting point for extending the language.

trait Versionable[T] {
   self: { def copy(version: Int): T } =>
   val version = 0
   def incrementVersion = copy(version = version + 1)
}

case class Customer(name: String, override val version: Int) 
      extends Versionable[Customer] {
   def changeName(newName: String) = copy(name = newName)
}

The code would work if the compiler recognized the Customer class's copy method as conforming to the method defined in Versionable's self-type annotation, which seems like a natural way to use named and default parameters.