Initializing values in Traits

Question

I have an enormous class that I want to break in many traits. Each part of my class has a set of vals not used by the other parts. These parameters are read from a property file, sometimes with some calculation. I would like to have each trait be responsible for initializing its own variables. I would like these values to be private to the trait. Unfortunately, traits do not have constructors (which is what I really want).

What is the pattern for creating an object that mixes a set of traits, where the traits have values that need initializing?

Here is an example:

class Foo( properties: Properties ) extends Bar with Baz

trait Bar {
 private val something
}

trait Baz {
 private val somethingElse
}

How do I initialize Bar.something and Baz.somethingElse without either making them abstract and non-private, or adding an init() method and making them vars?

Thank you Peter

Answer 1

What about early initialization?

trait A {
  val f: String
  val a = "I would have used " + f
}

trait B {
  val f: String
  val b = "I would have used " + f + " too!"
}

class C extends { val f = "the string" } with A with B

If you throw this into a REPL:

scala> List(c.a, c.b).map(println _)
I would have used the string
I would have used the string too!