Subtype codecs with Circe

circe-subtyping.scala

// ========== approach 1 ==========

sealed abstract class FooBase {
  def subType: String = this.getClass.getSimpleName
}
case class Foo(a: Int, b: String) extends FooBase
case class Bar(c: Float, d: Int) extends FooBase
val fooName = getClassName(Foo.getClass)
val barName = getClassName(Bar.getClass)

implicit val fooDecoder: Decoder[Foo] = deriveDecoder
implicit val fooEncoder: Encoder[Foo] = deriveEncoder
implicit val barDecoder: Decoder[Bar] = deriveDecoder
implicit val barEncoder: Encoder[Bar] = deriveEncoder

implicit val decodeBaseFoo: Decoder[FooBase] = new Decoder[FooBase] {
  final def apply(c: HCursor): Decoder.Result[FooBase] =
    c.downField("subType").as[String] flatMap {
      case `fooName` => c.as[Foo]
      case `barName` => c.as[Bar]
    }
}

implicit val encodeBaseFoo: Encoder[FooBase] = new Encoder[FooBase] {
  final def apply(fb: FooBase): Json = fb match {
    case f: Foo => f.asJson.mapObject(o => o.add("subType", Json.fromString(fooName)))
    case b: Bar => b.asJson.mapObject(o => o.add("subType", Json.fromString(barName)))
  }
}

// ========== approach 2 ==========

sealed abstract class FooBase
case class Foo(a: Int, b: String) extends FooBase
case class Bar(c: Float, d: Int) extends FooBase

implicit val fooDecoder: Decoder[Foo] = deriveDecoder
implicit val fooEncoder: Encoder[Foo] = deriveEncoder
implicit val barDecoder: Decoder[Bar] = deriveDecoder
implicit val barEncoder: Encoder[Bar] = deriveEncoder

implicit val fooBaseDecoder: Decoder[FooBase] = deriveDecoder
implicit val fooBaseEncoder: Encoder[FooBase] = deriveEncoder