与 Cats 和 Refined Types 一起使用时无法生成 Circe 解码器

Question

I wrote this code

import io.circe._
import io.circe.refined._
import cats.data._
import cats.implicits._
import eu.timepit.refined.auto._

final case class Translation(lang: LanguageCode, name: ProductName)
final case class Product(id: ProductId, names: List[Translation])

object Translation {
    implicit val decode: Decoder[Translation] = Decoder.forProduct2("lang", "name")(Translation.apply)
    implicit val encode: Encoder[Translation] = Encoder.forProduct2("lang", "name")(t => (t.lang, t.name))
}

object Product {
    implicit val decode: Decoder[Product] = Decoder.forProduct2("id", "names")(Product.apply)
    implicit val encode: Encoder[Product] = Encoder.forProduct2("id", "names")(p => (p.id, p.names))
}

This works fine and it compiles. but if I change my Product Type to use a cats non-empty set.

final case class Product(id: ProductId, names: NonEmptySet[Translation])

I get a compile time error

could not find implicit value for parameter decodeA1:
io.circe.Decoder[cats.data.NonEmptySet[com.abhi.models.Translation]]"

What can I do so that it auto-generates the decoder for the NonEmptySet just like it does for the List?

Answer 1

Looking at the circe source code it provides a Decoder[NonEmptySet[A]] if given a Decoder[A] and a Order[A] .

implicit final def decodeNonEmptySet[A](implicit decodeA: Decoder[A], orderA: Order[A]): Decoder[NonEmptySet[A]] =
    new NonEmptySeqDecoder[A, SortedSet, NonEmptySet[A]](decodeA) {
      final protected def createBuilder(): Builder[A, SortedSet[A]] = SortedSet.newBuilder[A](Order.catsKernelOrderingForOrder(orderA))
      final protected val create: (A, SortedSet[A]) => NonEmptySet[A] = (h, t) => NonEmptySet(h, t)
    }

My guess is you're missing an implicit for Order[Translation] .