如何向Scala枚举对象添加方法? [英] How to add a method to a Scala Enumeration object?

问题描述

我正在使用Scala 2.8并定义这样的枚举:

I'm using Scala 2.8 and defining an Enumeration like this:

object Stooges extends Enumeration {
  type Stooge = Value
  val Larry, Curly, Moe = Value
}

我想向此枚举添加一个方法，该方法循环到下一个"隐藏对象.我可以在Stooges之外定义这种方法，并且可以在测试程序中正常工作:

And I want to add a method to this Enumeration that cycles to the "next" stooge. I can define such a method outside Stooges and this works in a test program just fine:

def nextStooge(v:Stooges.Stooge):Stooges.Stooge =
  Stooges((v.id+1) % Stooges.values.size)

我真正想要的是将这种方法添加到Stooges中，而我尝试做这种事情(同时使用Stooges.Stooge和Stooges.Value).那些都编译.但是运行这样的程序:

What I'd really like is to add this method to Stooges and I have tried doing such a thing (using both Stooges.Stooge and Stooges.Value). Those both compile. But running a program like this:

import Stooges._
object App extends Application {
  println(Stooges.nextStooge(Larry))
}

产量:

Exception in thread "main" java.lang.ExceptionInInitializerError
        at demo.App.main(Stooges.scala)
Caused by: java.lang.IllegalArgumentException: wrong number of arguments
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:592)
        at scala.Enumeration$$anonfun$scala$Enumeration$$nameOf$2.apply(Enumeration.scala:176)
        at scala.Enumeration$$anonfun$scala$Enumeration$$nameOf$2.apply(Enumeration.scala:171)
        at scala.collection.TraversableLike$WithFilter$$anonfun$foreach$1.apply(TraversableLike.scala:1200)
        at scala.collection.IndexedSeqLike$class.foreach(IndexedSeqLike.scala:85)
        at scala.collection.mutable.ArrayOps.foreach(ArrayOps.scala:20)
        at scala.collection.TraversableLike$WithFilter.foreach(TraversableLike.scala:1199)
        at scala.Enumeration.scala$Enumeration$$nameOf(Enumeration.scala:171)
        at scala.Enumeration$Val.toString(Enumeration.scala:237)
        at java.lang.String.valueOf(String.java:2615)
        at java.io.PrintStream.print(PrintStream.java:616)
        at java.io.PrintStream.println(PrintStream.java:753)
        at scala.Console$.println(Console.scala:198)
        at scala.Predef$.println(Predef.scala:152)
        at demo.App$.<init>(Stooges.scala:14)
        at demo.App$.<clinit>(Stooges.scala)

这是一个错误还是一个坏主意?

Is this a bug or just a bad idea?

推荐答案

这对我有用:

scala> object Stooges extends Enumeration {
     |   type Stooge = Value
     |   val Larry = Value("Larry")
     |   val Curly = Value("Curly")
     |   val Moe = Value("Moe")
     |
     |   def nextStooge(v:Stooges.Stooge) = Stooges((v.id+1) % Stooges.maxId)
     | }
defined module Stooges

scala>

scala> import Stooges._
import Stooges._

scala> nextStooge(Larry)
res0: Stooges.Value = Curly

scala> nextStooge(Curly)
res1: Stooges.Value = Moe

scala> nextStooge(Moe)
res2: Stooges.Value = Larry

能够说出 Larry.nextStooge 而不是 nextStooge(Larry)，在定义上会更好.我想您必须使用一个自定义的密封类来实现它.

It would be definetively nicer to be able to say Larry.nextStooge instead of nextStooge(Larry). I suppose you have to implement that with a custom sealed class.

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