extension-problem-functional-way.sc

gistfile1.sc

import VendorLib.JsonString

// rules :
// 1) You can't change VendorLib
// 2) You can't change UserCode
// 3) Type safety
object VendorLib {
  sealed trait Json
  case class JsonString(s: String)            extends Json
  case class JsonArray(a: Seq[Json])          extends Json
  case class JsonObject(m: Map[String, Json]) extends Json
}

object UserLib {
  trait Alive
  case class Human(name: String, like: Seq[Alive]) extends Alive
  case class Dog(companion: Human)                 extends Alive
  import VendorLib.*
  def toJson(x: Alive): Json = x match
    case Human(name, like) => JsonObject(Map("name" -> JsonString(name), "like" -> JsonArray(like.map(l => toJson(l)))))
    case Dog(companion)    => JsonObject(Map("companion" -> toJson(companion)))

}

val louis  = UserLib.Human("louis", List.empty)
val satan  = UserLib.Dog(louis)
val jerome = UserLib.Human("jerome", List(satan))

println(UserLib.toJson(jerome))

object UserLib2 {
  case class Plant() extends UserLib.Alive

  import UserLib.*
  import VendorLib.*
  def toUppercaseJson(x: UserLib.Alive): VendorLib.Json = x match
    case Human(name, like) =>
      JsonObject(Map("NAME" -> JsonString(name), "LIKE" -> JsonArray(like.map(l => toUppercaseJson(l)))))
    case Dog(companion) => JsonObject(Map("COMPANION" -> toUppercaseJson(companion)))
    case Plant()        => JsonString("i am a plant".toUpperCase)
}

val arbre = UserLib2.Plant()
val roger = UserLib.Human("roguer", List(arbre))
println(UserLib2.toUppercaseJson(roger))