如何在Scala中添加一个枚举方法？

enums java enumeration scala

2022-09-01 03:26:20

在Java中，您可以：

public enum Enum {
    ONE {
        public String method() {
            return "1";
        }
    },
    TWO {
        public String method() {
            return "2";
        }
    },
    THREE {
        public String method() {
            return "3";
        }
    };

    public abstract String method();
}

你是如何在Scala中做到这一点的？

编辑/有用的链接：

答案 1

下面是通过扩展 Enumeration.Val 类向 scala 枚举添加属性的示例。

object Planet extends Enumeration { 
   protected case class Val(val mass: Double, val radius: Double) extends super.Val { 
     def surfaceGravity: Double = Planet.G * mass / (radius * radius) 
     def surfaceWeight(otherMass: Double): Double = otherMass * surfaceGravity 
   } 
   implicit def valueToPlanetVal(x: Value) = x.asInstanceOf[Val] 

   val G: Double = 6.67300E-11 
   val Mercury = Val(3.303e+23, 2.4397e6) 
   val Venus   = Val(4.869e+24, 6.0518e6) 
   val Earth   = Val(5.976e+24, 6.37814e6) 
   val Mars    = Val(6.421e+23, 3.3972e6) 
   val Jupiter = Val(1.9e+27, 7.1492e7) 
   val Saturn  = Val(5.688e+26, 6.0268e7) 
   val Uranus  = Val(8.686e+25, 2.5559e7) 
   val Neptune = Val(1.024e+26, 2.4746e7) 
} 

scala> Planet.values.filter(_.radius > 7.0e6) 
res16: Planet.ValueSet = Planet.ValueSet(Jupiter, Saturn, Uranus, Neptune)

答案 2

基于Chris的解决方案，您可以通过隐式转换实现更好的语法：

object Suit extends Enumeration {
   val Clubs, Diamonds, Hearts, Spades = Value

   class SuitValue(suit: Value) {
      def isRed = !isBlack
      def isBlack = suit match {
         case Clubs | Spades => true
         case _              => false
      }
   }

   implicit def value2SuitValue(suit: Value) = new SuitValue(suit)
}

然后，您可以调用，例如，.Suit.Clubs.isRed