safe_parse_list_elements.sc

//> using dep com.lihaoyi::pprint:0.8.1
//> using dep io.circe::circe-core::0.14.6
//> using dep io.circe::circe-generic::0.14.6
import io.circe._
import io.circe.generic.semiauto._
import io.circe.Json._
import pprint._

final case class Cat(name: String)
object Cat:
  given decoder: Decoder[Cat] = deriveDecoder

given deriveSafeDecoder[A: Decoder]: Decoder[List[Either[DecodingFailure, A]]] =
  Decoder[List[Json]].map(_.map(_.as[A]))

type Result[A] = (List[DecodingFailure], List[A])

given partitioned[A: Decoder]: Decoder[Result[A]] =
  deriveSafeDecoder[A].map(
    _.foldLeft((List.empty[DecodingFailure], List.empty[A])) {
      case ((ls, rs), Left(l))  => (l :: ls, rs)
      case ((ls, rs), Right(r)) => (ls, r :: rs)
    }
  )


val input = arr(
  obj("name" -> fromString("nyan")),
  obj("name" -> fromString("meow")),
  obj("name" -> fromInt(1234)),
  obj("name" -> fromString("miaou"))
)

pprintln(partitioned[Cat].apply(input.hcursor))