比较无法排序的可枚举值答案

【问题标题】：Compare enumerable values that can't be sorted比较无法排序的可枚举值
【发布时间】：2020-03-03 01:16:34
【问题描述】：

我需要比较可枚举的值，但这些值的集合不是 ordered。

我有 Rock,Paper,Scissors 的值，例如，我希望 Rock 输给 Paper。没有出现这种情况，看最后两行代码

object Move extends Enumeration {
    type Move = Value
    val Rock, Paper, Scissors = Value
}
import Move._

object MoveOrdering extends Ordering[Move] {
    def compare(m1: Move, m2: Move) = {
        (m1, m2) match {
            case (Rock, Paper) => -1
            case (Rock, Scissors) => +1
            case (Paper, Rock) => +1
            case (Paper, Scissors) => -1
            case (Scissors, Paper) => +1
            case (Scissors, Rock) => -1
            case _ => 0
        }
    }
}

Rock > Scissors // evaluates to false, I'd expect true
Scissors < Rock // evaluates to false, I'd expect true

我遗漏了什么使上面的代码没有按预期工作？

【问题讨论】：

什么不起作用？

标签： scala enumerable

【解决方案1】：

我认为您希望Rock > Scissors 会考虑使用MoveOrdering。

这就是它现在的工作方式，因为abstract class Value extends Ordered[Value] 的默认实现为：

 abstract class Value extends Ordered[Value] with Serializable {
    /** the id and bit location of this enumeration value */
    def id: Int
    /** a marker so we can tell whose values belong to whom come reflective-naming time */
    private[Enumeration] val outerEnum = thisenum

    override def compare(that: Value): Int =
      if (this.id < that.id) -1
      else if (this.id == that.id) 0
      else 1

所以默认情况下它使用枚举中定义的元素的index。在您的情况下，默认情况下Rock < Paper < Scissors。如果您想使用自定义排序：

object Move extends Enumeration{
  type Move = Value
  val Paper, Scissors, Rock = Value
}
import Move._
implicit object MoveOrdering extends Ordering[Move] {
  def compare(m1: Move, m2: Move) = {
    (m1, m2) match {
      case (Rock, Paper) => -1
      case (Rock, Scissors) => +1
      case (Paper, Rock) => +1
      case (Paper, Scissors) => -1
      case (Scissors, Paper) => +1
      case (Scissors, Rock) => -1
      case _ => 0
    }
  }
}

implicit val o = implicitly[Ordering[Move]]

println(List(Rock, Scissors, Paper).sorted)
println(o.lt(Rock, Scissors))

【讨论】：