typesafebuilder.scala

object TypeSafeBuilder {

  sealed trait BuilderStatus
  object Satisfied extends BuilderStatus
  object NotSatisfied extends BuilderStatus

  case class Cat(name: String, age: Int)

  object CatBuilder {
    def apply() = new CatBuilder[NotSatisfied.type, NotSatisfied.type](None, None)
    implicit class BuildableCatBuilder(cb: CatBuilder[Satisfied.type, Satisfied.type]) {
      def build(): Cat = cb.hiddenBuild()
    }
  }
  
  class CatBuilder[A <: BuilderStatus, B <: BuilderStatus] private (name: Option[String], age: Option[Int]) {
    def withName(s: String) = new CatBuilder[Satisfied.type, B](Some(s), age)
    def withAge(a: Int) = new CatBuilder[A, Satisfied.type ](name, Some(a))
    private def hiddenBuild(): Cat = Cat(name.get, age.get)
  }
  
  
  CatBuilder().withAge(2).withName("Terry").build() //  works
  CatBuilder().withName("Bob").build() // doesn't compile

}