Scala Cookbook

10.26. Creating and Using Enumerations

Problem

You want to use an enumeration (a set of named values that act as constants) in your application.

Solution

Extend the scala.Enumeration class to create your enumeration:

package com.acme.app {
  object Margin extends Enumeration {
    type Margin = Value
    val TOP, BOTTOM, LEFT, RIGHT = Value
  }
}

Then import the enumeration to use it in your application:

object Main extends App {

  import com.acme.app.Margin._

  // use an enumeration value in a test
  var currentMargin = TOP

  // later in the code ...
  if (currentMargin == TOP) println("working on Top")

  // print all the enumeration values
  import com.acme.app.Margin
  Margin.values foreach println

}

Enumerations are useful tool for creating groups of constants, such as days of the week, weeks of the year, and many other situations where you have a group of related, constant values.

You can also use the following approach, but it generates about four times as much code as an Enumeration, most of which you won’t need if your sole purpose is to use it like an enumeration:

// a much "heavier" approach
package com.acme.app {
  trait Margin
  case object TOP extends Margin
  case object RIGHT extends Margin
  case object BOTTOM extends Margin
  case object LEFT extends Margin
}

See Also

Scala Enumeration class