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?

Answer 1

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]
}

Answer 2

Look at shapeless coproducts

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

Answer 3

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:

• http://docs.scala-lang.org/tutorials/tour/variances.html
• How do I setup multiple type bounds in Scala?

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