functional-dsl-blog-10.scala

functional-dsl-blog-10.scala

  sealed trait EmailFilter { self =>
    def &&(that: EmailFilter): EmailFilter = EmailFilter.And(self, that)
    def ||(that: EmailFilter): EmailFilter = (self.negate && that.negate).negate
    def negate : EmailFilter = EmailFilter.Not(self)

    import EmailFilter._
    def run(email: Email): Boolean = self match {
      case Always => true
      case Not(filter: EmailFilter) => !filter.run(email)
      case And(left: EmailFilter, right: EmailFilter) =>
        left.run(email) && right.run(email)
        // This uses Scala's Boolean.&&, not the EmailFilter.&& defined in line 2
    }
  }
  object EmailFilter {
    final case object Always                                    extends EmailFilter
    final case class Not(filter: EmailFilter)                   extends EmailFilter
    final case class And(left: EmailFilter, right: EmailFilter) extends EmailFilter

    val always: EmailFilter = Always
  }