Type to capture either integer, float or a string value and then do pattern matching in Scala

问题

In Ocaml it is possible to define something like this:

type univ = I of int | F of float | S of string ;;

In order to create objects with like this:

let pol_list = [I 3; F 4.3; S "potato"; I 4];;

And then do pattern matching to extract a certain property (Either value or length depending on the case) like this:

let get_value val =
  match val with
  | I v -> v
  | F v -> (int_of_float v)
  | S s -> (String.length s)

How would this be done in Scala? If not possible, is there another similar alternative?

回答1:

I don't know OCaml, but it seems univ is an Algebraic Data Type, which you could model in Scala with a sealed trait and some case classes (which is more verbose than in OCaml) :

sealed trait Univ extends Product with Serializable
case class I(i: Int) extends Univ
case class F(f: Float) extends Univ
case class S(s: String) extends Univ

val polList = List(I(3), F(4.3f), S("potato"), I(4))

def getValue(v: Univ): Int = v match {
  case I(i) => i
  case F(f) => f.toInt
  case S(s) => s.length
}

polList.map(getValue) // List[Int] = List(3, 4, 6, 4)

回答2:

Maybe something like that:

val mix = List(1, "foo", 4.5)

val normalized = for (e <- mix) yield {
  e match {
    case s: String => s.length
    case i: Int => i
    case d: Double => d.toInt
  }
}

println(normalized)

List(1, 3, 4)

来源：https://stackoverflow.com/questions/33384189/type-to-capture-either-integer-float-or-a-string-value-and-then-do-pattern-matc