在Scala中创建一个使用枚举作为键的Map的语法是什么？

Question

please see the below code. This line is marked as incorrect by Eclipse:

var map = Map[MyEnum,Point]()

I am trying to do the scala equivalent of Java:

private enum Letters{ A,B,C}
private Map<Letters,Integer> thing= new HashMap<Letters,Integer> ();

And this is the file/context in which it is written.

class Point(var x:Int = 0, var y:Int = 0, var hasBeenSet:Boolean = false){

}

object MyEnum extends Enumeration{
    MyEnum = Value
    val UL,U,UR,L,R,DL,D,DR = Value
}

object MyEnumHolder {
  var map = Map[MyEnum,Point]()
  MyEnum.values.foreach(x => (map + (x -> new Point()) ) 
}

I am trying to initialize an instance of the map with each value of the enum mapped to an empty point (that's what is going on in the for each loop).

EDIT: Had to edit because I messed some things up editing the pasted code, but it should be valid now

Answer 1

var map = Map[MyEnum.Value, Point]()

or I prefer

import MyEnum._
var map = Map[MyEnum,Point]()

edit: To give a little explanation of what this means, in the enumeration Value is the name of both a type and a method. type MyEnum = Value is basically just declaring an alias for the Value type, and the next line val UL, U... = Value is calling the method to generate the enums, each of which has type MyEnum.Value . So when declaring the map, you have to refer to this type in order for the key to store enums. You could also use MyEnum.MyEnum , but the reason you declare the type alias in the first place is so you can import it into scope and be able to refer to it just as MyEnum .

Answer 2

你是不是把MyEnums在地图上，但值的MyEnum ：

var map = Map[MyEnum.Value, Point]()

Answer 3

object MyEnum extends Enumeration {
  type MyEnum = Value /* You were missing keyword "type" here */
  val UL,U,UR,L,R,DL,D,DR = Value
}

object MyEnumHolder {
  import MyEnum.MyEnum /* Import this, otherwise type MyEnum can't be found */

  var map = Map[MyEnum, String]()
  MyEnum.values.foreach(x => (map + (x -> x.toString)))
}

You might also want to have a look at Case classes vs Enumerations in Scala .

Answer 4

I got it to work with the following. The syntax is a bit wonky, I'll admit.

object MyEnum extends Enumeration {
    type MyEnum = Value
    val UL, U, UR, L, R, DL, D, DR = Value
}

object Main extends App {
    Map[MyEnum.MyEnum, String]()

}

Although I guess it can help for pluralization

object Diaries extends Enumeration {
    type Diary = Value
    val Steven, Jessica, Bob = Value
}

import Diaries._

val currentDiary = Steven

val interestingDiaries = List[Diary](Steven, Jessica)

So here Diaries is the list of Diary, and Diary is a specific diary in the list.