Free, Simple PhantomBuilder in scala

PhantomBuilder.scala

object PhantomBuilder extends App {

  object Builder {

    sealed trait State

    trait Checked extends State

    trait Unchecked extends State

    case class Tuple2StringBuilder[_1CHECK, _2CHECK](_1: Option[String],
                                                     _2: Option[String]) {
      def _01Set(str: String) = this.copy[Checked, _2CHECK](_1 = Some(str))

      def _02Set(str: String) = this.copy[_1CHECK, Checked](_2 = Some(str))
    }

    implicit class BuildOps(builder: Tuple2StringBuilder[Checked, Checked]) {
      def build = (builder._1.get, builder._2.get)
    }

    def tuple: Tuple2StringBuilder[Unchecked, Unchecked] =
      new Tuple2StringBuilder[Unchecked, Unchecked](None, None)
  }

  val tuple = Builder.tuple
    ._01Set("Marco")
    ._02Set("Tagliabosco")
    .build

  print(tuple)
}