http://www.scala-lang.org/docu/files/api/scala/Enumeration.html

示例使用

  object Main extends App {

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

    def isWorkingDay(d: WeekDay) = ! (d == Sat || d == Sun)

    WeekDay.values filter isWorkingDay foreach println
  }

从Scala 3开始，现在有一个enum关键字，它可以表示一组常量(和其他用例)

enum Color:
   case Red, Green, Blue

scala> val red = Color.Red
val red: Color = Red
scala> red.ordinal
val res0: Int = 0

http://www.scala-lang.org/docu/files/api/scala/Enumeration.html

示例使用

  object Main extends App {

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

    def isWorkingDay(d: WeekDay) = ! (d == Sat || d == Sun)

    WeekDay.values filter isWorkingDay foreach println
  }

有很多方法可以做。

1)使用符号。但是，除了在需要符号的地方不接受非符号之外，它不会为您提供任何类型安全性。我在这里只是为了完整起见才提到它。下面是一个用法示例:

def update(what: Symbol, where: Int, newValue: Array[Int]): MatrixInt =
  what match {
    case 'row => replaceRow(where, newValue)
    case 'col | 'column => replaceCol(where, newValue)
    case _ => throw new IllegalArgumentException
  }

// At REPL:   
scala> val a = unitMatrixInt(3)
a: teste7.MatrixInt =
/ 1 0 0 \
| 0 1 0 |
\ 0 0 1 /

scala> a('row, 1) = a.row(0)
res41: teste7.MatrixInt =
/ 1 0 0 \
| 1 0 0 |
\ 0 0 1 /

scala> a('column, 2) = a.row(0)
res42: teste7.MatrixInt =
/ 1 0 1 \
| 0 1 0 |
\ 0 0 0 /

2)使用类枚举:

object Dimension extends Enumeration {
  type Dimension = Value
  val Row, Column = Value
}

或者，如果你需要序列化或显示它:

object Dimension extends Enumeration("Row", "Column") {
  type Dimension = Value
  val Row, Column = Value
}

可以这样使用:

def update(what: Dimension, where: Int, newValue: Array[Int]): MatrixInt =
  what match {
    case Row => replaceRow(where, newValue)
    case Column => replaceCol(where, newValue)
  }

// At REPL:
scala> a(Row, 2) = a.row(1)
<console>:13: error: not found: value Row
       a(Row, 2) = a.row(1)
         ^

scala> a(Dimension.Row, 2) = a.row(1)
res1: teste.MatrixInt =
/ 1 0 0 \
| 0 1 0 |
\ 0 1 0 /

scala> import Dimension._
import Dimension._

scala> a(Row, 2) = a.row(1)
res2: teste.MatrixInt =
/ 1 0 0 \
| 0 1 0 |
\ 0 1 0 /

不幸的是，它不能确保所有匹配都被考虑在内。如果我忘记在匹配中放入Row或Column, Scala编译器不会警告我。因此，它给了我一些类型安全性，但并没有获得那么多。

3)案例对象:

sealed abstract class Dimension
case object Row extends Dimension
case object Column extends Dimension

现在，如果我在匹配时遗漏了大小写，编译器会警告我:

MatrixInt.scala:70: warning: match is not exhaustive!
missing combination         Column

    what match {
    ^
one warning found

它的使用方式几乎相同，甚至不需要导入:

scala> val a = unitMatrixInt(3)
a: teste3.MatrixInt =
/ 1 0 0 \
| 0 1 0 |
\ 0 0 1 /

scala> a(Row,2) = a.row(0)
res15: teste3.MatrixInt =
/ 1 0 0 \
| 0 1 0 |
\ 1 0 0 /

那么，您可能想知道为什么要使用Enumeration而不是case对象。事实上，case对象在很多时候都有优势，比如这里。Enumeration类有很多Collection方法，比如elements (Scala 2.8上的迭代器)，它返回一个iterator、map、flatMap、filter等。

这个答案基本上是从我博客中这篇文章中选择的一部分。

在Scala中，https://github.com/lloydmeta/enumeratum非常适合

项目是非常好的例子和文档

他们文档中的这个例子应该会让你感兴趣

import enumeratum._

sealed trait Greeting extends EnumEntry

object Greeting extends Enum[Greeting] {

  /*
   `findValues` is a protected method that invokes a macro to find all `Greeting` object declarations inside an `Enum`

   You use it to implement the `val values` member
  */
  val values = findValues

  case object Hello   extends Greeting
  case object GoodBye extends Greeting
  case object Hi      extends Greeting
  case object Bye     extends Greeting

}

// Object Greeting has a `withName(name: String)` method
Greeting.withName("Hello")
// => res0: Greeting = Hello

Greeting.withName("Haro")
// => java.lang.IllegalArgumentException: Haro is not a member of Enum (Hello, GoodBye, Hi, Bye)

// A safer alternative would be to use `withNameOption(name: String)` method which returns an Option[Greeting]
Greeting.withNameOption("Hello")
// => res1: Option[Greeting] = Some(Hello)

Greeting.withNameOption("Haro")
// => res2: Option[Greeting] = None

// It is also possible to use strings case insensitively
Greeting.withNameInsensitive("HeLLo")
// => res3: Greeting = Hello

Greeting.withNameInsensitiveOption("HeLLo")
// => res4: Option[Greeting] = Some(Hello)

// Uppercase-only strings may also be used
Greeting.withNameUppercaseOnly("HELLO")
// => res5: Greeting = Hello

Greeting.withNameUppercaseOnlyOption("HeLLo")
// => res6: Option[Greeting] = None

// Similarly, lowercase-only strings may also be used
Greeting.withNameLowercaseOnly("hello")
// => res7: Greeting = Hello

Greeting.withNameLowercaseOnlyOption("hello")
// => res8: Option[Greeting] = Some(Hello)

我必须说，上面skaffman从Scala文档中复制的示例在实践中用处有限(您还可以使用case对象)。

为了获得最接近Java Enum的东西(即使用合理的toString和valueOf方法——也许你要将枚举值持久化到数据库中)，你需要稍微修改它。如果你使用skaffman的代码:

WeekDay.valueOf("Sun") //returns None
WeekDay.Tue.toString   //returns Weekday(2)

鉴于使用以下声明:

object WeekDay extends Enumeration {
  type WeekDay = Value
  val Mon = Value("Mon")
  val Tue = Value("Tue") 
  ... etc
}

你会得到更合理的结果:

WeekDay.valueOf("Sun") //returns Some(Sun)
WeekDay.Tue.toString   //returns Tue