Scala shapeless HList to Json with io.circe

HListCodec.scala

import io.circe.{Encoder, JsonObject, ObjectEncoder}
import shapeless.{::, HList, HNil}
import scala.reflect.ClassTag

/**
  * val product = A(...) :: B(...) :: C(...) :: HNil
  * product.asJson
  *
  * {"a": {...}, "b": {...}, "c": {...}}
  */
object CodecHList {
  implicit val encodeHNil: ObjectEncoder[HNil] = ObjectEncoder.instance(_ => JsonObject.empty)

  implicit def encodeHCons[H: ClassTag, T <: HList](implicit
    encodeH: Encoder[H],
    encodeT: ObjectEncoder[T],
    tag: ClassTag[H]
  ): ObjectEncoder[H :: T] = ObjectEncoder.instance {
    case h :: t => (tag.runtimeClass.getSimpleName.toLowerCase -> encodeH(h)) +: encodeT.encodeObject(t)
  }
}


//
//
import io.circe.syntax._
import io.circe.generic.auto._

case class A(a: String)
case class B(b: Int)
case class C(c: Double)

val gen  = A("test") :: B(1) :: C(1.0) :: HNil
val json = gen.asJson