Question

官方Scala Dotty团队在（https://d-d.me/talks/scalaworld2015/#/12）

中展示了这个例子

object DaysOfTheWeek {
  object Mon
  object Tue
  object Wed
  object Thu
  object Fri
  object Sat
  object Sun

  type Weekend = Sat.type | Sun.type
  type Workweek = Mon.type | Tue.type | Wed.type | Thu.type | Fri.type
  type All = Weekend | Workweek
}

如果我使用最新的Dotty每晚构建，这个帖子是＆＃34; 0.1.1-20170322-5fd7a95-NIGHTLY＆＃34;，那么这个例子会导致这些错误：

Error:(13, 18) Singleton type DaysOfTheWeek.Sat.type is not allowed in a union type
Error:(13, 29) Singleton type DaysOfTheWeek.Sun.type is not allowed in a union type
Error:(14, 19) Singleton type DaysOfTheWeek.Mon.type is not allowed in a union type
Error:(14, 30) Singleton type DaysOfTheWeek.Tue.type is not allowed in a union type
Error:(14, 41) Singleton type DaysOfTheWeek.Wed.type is not allowed in a union type
Error:(14, 52) Singleton type DaysOfTheWeek.Thu.type is not allowed in a union type
Error:(14, 63) Singleton type DaysOfTheWeek.Fri.type is not allowed in a union type

有没有办法让这个官方的例子有效？

Answer 1

现在可以使用：

enum DaysOfTheWeek {
case Mon
case Tue
case Wed
case Thu
case Fri
case Sat
case Sun
  type Weekend = Sat.type | Sun.type
  type Workweek = Mon.type | Tue.type | Wed.type | Thu.type | Fri.type
  type All = Weekend | Workweek
}

链接到Scastie

Answer 2

我用枚举和更新的dotty得到的最远的是

enum class DaysOfTheWeek
object DaysOfTheWeek {
case Mon
case Tue
case Wed
case Thu
case Fri
case Sat
case Sun;

  type Weekend = Sat.type | Sun.type;
  type Workweek = Mon.type | Tue.type | Wed.type | Thu.type | Fri.type;
  type All = Weekend.type | Workweek.type;

}

仍会产生相同的错误，但可能会在此处解决：https://github.com/lampepfl/dotty/issues/1551

Scala Dotty联盟类型DaysOfTheWeek示例

2 个答案: