How to get Enumeration Value's Enumeration definition?

问题

object TestEnum extends Enumeration{
  val One = Value("One")
  val Two,Three= Value
}
println(TestEnum.One.getClass)
println(TestEnum.One.getClass.getDeclaringClass)//get Enumeration

So my question is how to get Class[TestEnum] from TestEnum.One?

Thanks.

回答1:

I don't think you can unfortunately. TestEnum.One is really just an instance of the class Enumeration#Value. In fact, it's lots worse than just this - your enumeration values are all erased by type to the same thing:

object Weekday extends Enumeration {
  val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
}

def foo(w: Weekday.Value)
def foo(e: TestEnum.Value) //won't compile as they erase to same type

As the instances of your enumeration are just instances of Enumeration#Value, their declaring class is just scala.Enumeration.

It's frustrating but it seems like these scala enums are worse than useless; if you pass them through serialization (at least in 2.7.7), then you can't do equality checks either!

回答2:

I am going to post a link to the Enum type that I wrote due to the limitations you mentioned. I don't use the built in enumeration type as I find it very limiting. Though it doesn't have the feature you would like (get the Enumeration from an Element), it would be pretty trivial to add it. Feel free to use it in any way if you find it helpful.

(source & test / example): http://gist.github.com/282446

BTW If you like and want help adding the container to the EnumElement let me know.

回答3:

In my opinion there is a simple solution for not dealing with Scala Enumerations: use Java enum-s instead. Scala has supported cross-compiling for a while now and it's easy to just add a Java enum in your Scala source folder.

来源：https://stackoverflow.com/questions/2100730/how-to-get-enumeration-values-enumeration-definition

标签

scala

enumeration