Scala枚举:选择一些值作为类型

Question

考虑WeekDays枚举:

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

现在我想定义一个只能在周末作为值的变量,例如:

val weekend: WeekDay.Sat | WeekDay.Sun

但显然这不是正确的Scala语法.我有什么方法可以做或近似这个？

Answer 1

只需用Google搜索"Scala枚举",然后点击第二个链接.简而言之,引用Martin Odersky的话说,枚举是指具有名称和顺序的简单整数常量.如果需要类型,则应使用案例类.因为周末也是工作日,所以听起来遗传是合适的:

sealed trait Weekday
sealed trait WorkDay extends Weekday
case object Monday extends WorkDay

sealed trait WeekendDay extends Weekday
case object Saturday extends WeekendDay
case object Sunday extends WeekendDay


object Main {     
    def onlyWeekendDays(d: WeekendDay) {
        println(d)
    }
    def allDays( d: Weekday ) {}

    def test() {
        onlyWeekendDays( Saturday );
        allDays( Saturday );
        allDays( Monday );
        // this fails to type-check: onlyWeekendDays( Monday );
    }
}