Another alternative to the Builder pattern in Scala 2.8 is to use immutable case classes with default arguments and named parameters. Its a little different but the effect is smart defaults, all values specified and things only specified once with syntax checking…
The following uses Strings for the values for brevity/speed…
scala> case class Pizza(ingredients: Traversable[String], base: String = "Normal", topping: String = "Mozzarella")
defined class Pizza
scala> val p1 = Pizza(Seq("Ham", "Mushroom"))
p1: Pizza = Pizza(List(Ham, Mushroom),Normal,Mozzarella)
scala> val p2 = Pizza(Seq("Mushroom"), topping = "Edam")
p2: Pizza = Pizza(List(Mushroom),Normal,Edam)
scala> val p3 = Pizza(Seq("Ham", "Pineapple"), topping = "Edam", base = "Small")
p3: Pizza = Pizza(List(Ham, Pineapple),Small,Edam)
You can then also use existing immutable instances as kinda builders too…
scala> val lp2 = p3.copy(base = "Large")
lp2: Pizza = Pizza(List(Ham, Pineapple),Large,Edam)