How can I dynamically (runtime) generate a sorted collection in Scala using the java.lang.reflect.Type?

Question

Given an array of items I need to generate a sorted collection in Scala for a java.lang.reflect.Type but I'm unable to do so. The following snippet might explain better.

  def buildList(paramType: Type): SortedSet[_] = {
    val collection = new Array[Any](5)
    for (i <- 0 until 5) {
      collection(i) = new EasyRandom().nextObject(paramType.asInstanceOf[Class[Any]])
    }
    SortedSet(collection:_*)
  }

I'm unable to do as I get the error "No implicits found for parameter ord: Ordering[Any]". I'm able to work around this if I swap to an unsorted type such as Set .

  def buildList(paramType: Type): Set[_] = {
    val collection = new Array[Any](5)
    for (i <- 0 until 5) {
      collection(i) = new EasyRandom().nextObject(paramType.asInstanceOf[Class[Any]])
    }
    Set(collection:_*)
  }

How can I dynamically build a sorted set at runtime? I've been looking into how Jackson tries to achieve the same but I couldn't quite follow how to get T here: https://github.com/FasterXML/jackson-module-scala/blob/0e926622ea4e8cef16dd757fa85400a0b9dcd1d3/src/main/scala/com/fasterxml/jackson/module/scala/introspect/OrderingLocator.scala#L21

(Please excuse me if my question is unclear.)

Answer 1

This happens because SortedSet needs a contextual (implicit) Ordering type class instance for a given type A

However, as Luis said on the comment section, I'd strongly advice you against using this approach and using a safer, strongly typed one, instead.

Generating random case classes (which I suppose you're using since you're using Scala) should be easy with the help of some libraries like magnolia . That would turn your code into something like this:

def randomList[A : Ordering : Arbitrary]: SortedSet[A] = {
  val arb: Arbitrary[A] = implicitly[Arbitrary[A]]
  val sampleData = (1 to 5).map(arb.arbitrary.sample)

  SortedSet(sampleData)
}

This approach involves some heavy concepts like implicits and type classes, but is way safer.