使用 Scala Enumeration 的星期幾

可以通過擴充套件 Enumeration 來建立類似 Java 的列舉 。

object WeekDays extends Enumeration {
  val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
}

def isWeekend(day: WeekDays.Value): Boolean = day match {
  case WeekDays.Sat | WeekDays.Sun => true
  case _ => false
}

isWeekend(WeekDays.Sun)
res0: Boolean = true

也可以為列舉中的值新增一個人類可讀的名稱：

object WeekDays extends Enumeration {
      val Mon = Value("Monday")
      val Tue = Value("Tuesday")
      val Wed = Value("Wednesday")
      val Thu = Value("Thursday")
      val Fri = Value("Friday")
      val Sat = Value("Saturday")
      val Sun = Value("Sunday")
}

println(WeekDays.Mon)
>> Monday

WeekDays.withName("Monday") == WeekDays.Mon
>> res0: Boolean = true

請注意不那麼型別的安全行為，其中不同的列舉可以評估為相同的例項型別：

object Parity extends Enumeration {
   val Even, Odd = Value
}
  
WeekDays.Mon.isInstanceOf[Parity.Value]
>> res1: Boolean = true