How to pass array of types in Scala?

Question

I am trying to create a method that will take a list of Objects and a list of Types and then check whether a particular object matches a particular type.

I tried to create a dummy example. In the following code validate method takes list of objects and a List of type then tried to validate the types of each object. I know following code is wrong but I just created to communicate the problem, it would be really great if you can tell me how can I do this in Scala.

object T extends App {
  trait MyT
  case class A(a: Int) extends MyT
  case class B(b: Int) extends MyT

  def validate(values: Seq[Any], types: Seq[MyT]): Seq[Boolean] =
    for ((v, ty: MyT) ← values.zip(types)) yield v.isInstanceOf[ty]

  // create objects
  val a = A(1)
  val b = B(1)

  // call validate method 
  validate(Seq(a, b), Seq(A, B))

}

Types are not objects. They cannot be stored in containers. But you can use Class or TypeTags. — SwiftMango
– SwiftMango, Commented Jan 20, 2022 at 6:16
Does it need to work with generic types? Otherwise just go with Class. — Gaël J
– Gaël J, Commented Jan 20, 2022 at 6:52
@GaëlJ All Types I would like to pass in the second argument of validate method are going be sub type of a trait. — Abhishek Gupta
– Abhishek Gupta, Commented Jan 20, 2022 at 7:50

Luis Miguel Mejía Suárez · Accepted Answer · 2022-01-20 15:23:58Z

3

Types are not values, so you can't have a list of them.
But, you may use Class instead:

def validate(values: Seq[Any], types: Seq[Class[_ <: MyT]]): Seq[Boolean] =
  values.lazyZip(types).map {
    case (v, c) =>
      c.isInstance(v)
  }

Which can be used like this:

validate(Seq(a, b), Seq(classOf[A], classOf[B]))
// res: Seq[Boolean] = List(true, true)

You can see the code running here.

However, note that this will break if your classes start to have type parameters due to type erasure.

Note, I personally don't recommend this code since, IMHO, the very definition of validate is a code smell and I would bet you have a design error that lead to this situation.

I recommend searching for a way to avoid this situation and solve the root problem.

edited Jan 20, 2022 at 15:23

answered Jan 20, 2022 at 13:27

Luis Miguel Mejía Suárez

23k4 gold badges31 silver badges50 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How to pass array of types in Scala?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related