Scala variable with multiple types

Question

There is Either in scala which allow a variable to have 2 types value.

val x: Either[String, Int] = Left("apple")

However, I want to have more than 2 types for variable x e.g. {String, Int, Double, List[String] }.

e.g. val x:[type can be either String, Int, Double or List[String]]
//So that I can store either String, Int, Double, List[String] value in x.

Is there any way to achieve this?

*I want to have more than 2 types for variable*. Can you elaborate on what that actually means, perhaps by giving an example? — Yuval Itzchakov, Apr 19 '17 at 11:56
@JörgWMittag, is there any simpler way, because i realize that, I also have to provide Left/Right in nested way. e.g. for Int - Left(Left(Right(12))). Isn't there a way so that I can do like x = 12? — Ra Ka, Apr 19 '17 at 12:03

Yuval Itzchakov · Accepted Answer · 2019-05-13T07:19:09.373

IMO the most natural way to express this is to create an ADT (Algebraic Data Type):

sealed trait Foo
final case class Bar(s: String) extends Foo
final case class Baz(i: Int) extends Foo
final case class Fizz(d: Double) extends Foo
final case class Buzz(l: List[String]) extends Foo

And now you can pattern match on Foo:

val f: Foo = ???
f match {
  case Bar(s) => // String
  case Baz(i) => // Int
  case Fizz(d) => // Double
  case Buzz(l) => // List[String]
}

score 12 · Answer 2 · answered Apr 19 '17 at 12:12

12

Look at shapeless coproducts

"shapeless has a Coproduct type, a generalization of Scala's Either to an arbitrary number of choices"

answered Apr 19 '17 at 12:12

Arnon Rotem-Gal-Oz

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This seems to be the exactly what I wanted, however, I'll won't be able to use any external library right now but will consider this later. Btw, its very helpful to know about it. Thank you. – Ra Ka Apr 19 '17 at 16:30

score 4 · Answer 3 · edited May 23 '17 at 12:09

Not sure what your exact use case is but check this out: scala type alias - how to have a type that represent multiple data types

Basically you create a trait represents an umbrella/parent class. Then you define multiple classes that extend the parent trait and put the parent trait as the expected parameter type in your function. Then you can pass any type that extends that parent trait.

You have to wrap the subtypes, but this allows you to have one type that represents multiple types.

Another way could be to use generic types and type bounds. These articles talk about these two subjects:

I'm still learning Scala, but hope this helps! :)

Your answer contains much information and is very helpful. Thank you. :) — Ra Ka, Apr 19 '17 at 16:32

Scala variable with multiple types

3 Answers3

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