Scala中的丰富枚举 [英] Rich enumeration in Scala

问题描述

我正在寻找一种在Scala中实现丰富枚举的机制，就像您在Java中将抽象方法添加到枚举并在枚举实例中实现它们的方式一样。

I am looking for a mechanism to implement rich enumerations in Scala, the same way you can in Java add abstract methods to enums and implement them in the instances of of the enum.

请注意，使用密封的特征和case对象不是解决方案，因为除非我保留它们的列表，否则我将无法遍历现有的case对象，这对更改非常脆弱（尤其是通过其他不了解发生了什么的人）

Please note that using a sealed trait and case objects is not a solution, because I would not be able to iterate over the existing case objects, unless I mantain a list of them, which is very fragile to changes (especially by other people who don't understand what's going on there)

推荐答案

只需扩展 Val 。

object items extends Enumeration {

  val pen = Item("writing")
  val brush = Item("painting")

  final case class Item(key: String) extends Val {
    def kind: String = toString
  }
}

object Test {
  import items._
  def main(args: Array[String]) {
    println(pen.kind +" is for "+ pen.key)
    println(brush.key)
    println(items.values)
  }
}

或

object days extends Enumeration {
  case class Day(i: Int, name: String) extends Val(i, name) {
    def isWeekDay = i < 5
  }
  private def newDay() = new Day(nextId, null)
  val Mon, Tue, Wed, Thu, Fri, Sat, Sun = newDay()
  val daysOfTheWeek = values.toList.asInstanceOf[List[Day]]
}

object Test extends App {
  import days._
  println(Thu)
  println(days.values.toList mkString ",")
  for (d <- days.daysOfTheWeek) Console println s"$d is weekday? ${d.isWeekDay}"
}

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