Does anybody know how to make this test work using Shapeless.
package net.jtownson.swakka.jsonschema
import org.scalatest.FlatSpec
import org.scalatest.Matchers._
class OptionalFieldSpec extends FlatSpec {
case class A(i: Int, j: Option[Int])
"an extractor of some kind" should "get the (non)optional fields from a case class" in {
extractNonOptionalFieldNames[A] shouldBe List("i")
extractOptionalFieldNames[A] shouldBe List("j")
}
def extractNonOptionalFieldNames[T <: Product](/* implicit typeclass instances? */): List[String] = ???
def extractOptionalFieldNames[T <: Product]: List[String] = ???
}
I have no runtime instance of A or its Generic equivalent as I am working at creating a JsonSchema for case class A, which is independent of any given instance. The schema has a required field, which is a list of the non-optional fields. e.g.
{
"type" -> "object",
"required" -> ["i"],
"properties" -> {
"i" -> {
"type" -> "integer",
"format" -> "int32"
}
}
}
Something like this:
trait FieldNameExtractor[T] extends Serializable {
import shapeless.ops.hlist.{RightFolder, ToTraversable}
import shapeless.ops.record.Keys
import shapeless.{HList, HNil, LabelledGeneric, Poly2}
/**
* Extracts filtered field names for type [[T]],
* given a polymorphic function that acts as the type filter
*/
def extract[L <: HList, R <: HList, O <: HList](op: Poly2)(
implicit lgen: LabelledGeneric.Aux[T, L],
folder: RightFolder.Aux[L, HNil.type, op.type, R],
keys: Keys.Aux[R, O],
traversable: ToTraversable.Aux[O, List, Symbol]
): List[String] = {
val result = keys().to[List]
result.map(_.name)
}
}
object FieldNameExtractor {
def apply[T] = new FieldNameExtractor[T] {}
}
Usage:
import org.scalatest.FlatSpec
import org.scalatest.Matchers._
class Test extends FlatSpec {
/* type filters */
import shapeless.{HList, Poly2}
import shapeless.labelled.KeyTag, shapeless.tag.Tagged
type FilterO[A, T] = Option[A] with KeyTag[Symbol with Tagged[T], Option[A]]
trait Ignore extends Poly2 {
implicit def default[A, L <: HList] = at[A, L]((_, l) => l)
}
trait Accept extends Poly2 {
implicit def default[A, L <: HList] = at[A, L](_ :: _)
}
object allOptions extends Ignore {
implicit def option[A, T, L <: HList] = at[FilterO[A, T], L](_ :: _)
}
object noOptions extends Accept {
implicit def option[A, T, L <: HList] = at[FilterO[A, T], L]((_, l) => l)
}
"an extractor of some kind" should "get the (non)optional fields from a case class" in {
case class A(i: Int, j: Option[Int], k: String)
val fne = FieldNameExtractor[A]
fne.extract(noOptions) shouldBe List("i", "k") // extractNonOptionalFieldNames
fne.extract(allOptions) shouldBe List("j") // extractOptionalFieldNames
}
}