CODEWITHSUNDEEP
scalaenumeration
Eirik Sletteberg
Eirik Sletteberg

Reputation: 222

Using Enumerations as type parameters

I want to write a method like this:

def validate[T <: Enumeration](input: String)(implicit enum: T) : Seq[T]

that will take an input ("foo,bar,baz") and split it with commas - then compare to the enumerations given. For example, given this enum:

object Letter extends Enumeration {
  type Letter = Value
  val first = Value("A")
  val second = Value("B")
  val third = Value("C")
}

the expected output of validate[Letter]("A,B,C,D")

would be: Seq[Letter](first,second,third).

I've tried doing something like this:

val inputValues = input.split(",").toSeq
for {
  inputValue <- inputValues
  enumValue <- enum.values
  if enumValue.toString == inputValue
} yield enumValue

But it doesn't compile, because of the type system... is there another way to implement this?

Upvotes: 2

Views: 353

Answers (1)

Ashalynd
Ashalynd

Reputation: 12563

Cannot do it with implicit enum, but with explicit enum something like that seems to be possible:

scala> import scala.util.Try
scala> def validate[T <: Enumeration](input: String,  enum: T):Seq[T#Value]  = {
     | val inputValues = input.split(",").toSeq
     | for (value <- inputValues if Try(enum.withName(value)).isSuccess) yield enum.withName(value) }
validate: [T <: Enumeration](input: String, enum: T)Seq[T#Value]

scala> validate("A,B,D", Letter)
res12: Seq[Letter.Value] = ArrayBuffer(A, B)

Upvotes: 3

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