Mapping of String to Type - scala

Question

I am currently trying to write a method that takes a JSON (what API does not matter here) and validates it. I want the method to look something like this:
def validateJson(json, expectedType: Map[String, Type(?)], allowedVals: Map[String, Seq[expectedType(key)]]): Boolean
The problem is: I do have a method jsonfield.validate[expectedType] but I do not know how to pass an unknown number of useable type parameters associated with strings to a method.
I'd gladly use some runtime reflection if that is possible here, or any advanced feature necessary to make this work easily. Any suggestions appreciated.
PS: I am using Play Framework 2.6.3
Edit:
I am trying to use the passed types like this
val allowed = allowedVals(field) // a Set
// if field contents contained in allowed value set...
if( allowed(field.validate[expectedType(field)].get) ) foo

Answer 1

Maybe you can use varargs in runtime or abstract over arity in compile time or just use an HList:
def foo[L <: HList](l: L) = ???
trait A
trait B
trait C
val a: A = new A {}
val b: B = new B {}
val c: C = new C {}
foo[A :: B :: C :: HNil](a :: b :: c :: HNil)
Sounds like you're looking for dependent type/dependent function/polymorphic function:
import shapeless.Poly1
import shapeless.syntax.singleton._
object expectedTypeAndValue extends Poly1 {
implicit val aCase: Case.Aux["a", Int] = at["a"](_ => 1)
implicit val bCase: Case.Aux["b", Long] = at["b"](_ => 2L)
implicit val cCase: Case.Aux["c", Double] = at["c"](_ => 3.0)
}
def validateJson(json: Json): Boolean = {
val x: Long = expectedTypeAndValue["b"]("b".narrow)
???
}
in Typelevel Scala or
import shapeless.{Poly1, Witness}
import shapeless.syntax.singleton._
object expectedTypeAndValue extends Poly1 {
implicit val aCase: Case.Aux[Witness.`"a"`.T, Int] = at[Witness.`"a"`.T](_ => 1)
implicit val bCase: Case.Aux[Witness.`"b"`.T, Long] = at[Witness.`"b"`.T](_ => 2L)
implicit val cCase: Case.Aux[Witness.`"c"`.T, Double] = at[Witness.`"c"`.T](_ => 3.0)
}
def validateJson(json: Json): Boolean = {
val x: Long = expectedTypeAndValue[Witness.`"b"`.T]("b".narrow)
???
}
in Lightbend Scala (ordinary Scala).
You can create also custom type class:
trait ExpectedTypeAndVals[S <: String] {
type Out
def apply(s: S): Set[Out]
}
object ExpectedTypeAndVals {
type Aux[S <: String, Out0] = ExpectedTypeAndVals[S] {type Out = Out0}
implicit def mkExpectedTypeAndVals[S <: String]: ExpectedTypeAndVals.Aux[S, ???] =
new ExpectedTypeAndVals[S] {
override type Out = ???
override def apply(s: S): Set[Out] = ???
}
}
def allowed[S <: String, Out](json: Json)(implicit
typeAndVals: ExpectedTypeAndVals.Aux[S, Out]
): Boolean = {
val str: S = ???
val set: Set[Out] = typeAndVals(str)
???
}
if(allowed(json)) {
???
}