Scala的枚举类型不允许向枚举值中添加属性和/或方法。但是,使用这个新的MyEnumeration,您就可以实现这一点。
abstract class MyEnumeration {
type Value
private val vals = collection.mutable.LinkedHashMap[String, Value]()
protected trait ValuesCollector { self: Value =>
private val ordinal = vals.size
vals += (fieldNames(ordinal) -> self)
def getName = fieldNames(ordinal)
override def toString = getName
}
def apply(ordinal: Int) = vals(fieldNames(ordinal))
def apply(fldName: String) = vals(fldName)
def values = vals.values
def namedValues: collection.Map[String, Value] = vals
private val fieldNames = getClass.getMethods filter (m =>
m.getParameterTypes.isEmpty &&
classOf[ValuesCollector].isAssignableFrom(m.getReturnType) &&
m.getDeclaringClass != classOf[MyEnumeration]) map (_.getName)
}
这里展示了Scala中的Planet示例。
object Planet extends MyEnumeration {
case class Value(val mass: Double, val radius: Double) extends ValuesCollector {
private val G = 6.67300E-11;
def surfaceGravity = G * mass / (radius * radius)
def surfaceWeight(otherMass: Double) = otherMass * surfaceGravity
}
val MERCURY = Value(3.303e+23, 2.4397e6)
val VENUS = Value(4.869e+24, 6.0518e6)
val EARTH = Value(5.976e+24, 6.37814e6)
val MARS = Value(6.421e+23, 3.3972e6)
val JUPITER = Value(1.9e+27, 7.1492e7)
val SATURN = Value(5.688e+26, 6.0268e7)
val URANUS = Value(8.686e+25, 2.5559e7)
val NEPTUNE = Value(1.024e+26, 2.4746e7)
val PLUTO = Value(1.27e+22, 1.137e6)
}
object PlanetTest {
def main(args: Array[String]) {
val earthWeight = 175
val mass = earthWeight/Planet.EARTH.surfaceGravity
for (p <- Planet.values) println("Your weight on %s is %f" format (p, p.surfaceWeight(mass)))
}
}