尝试为 ADT 编写 Circe 编码器或解码器时遇到错误

【问题标题】：Encountering errors when trying to write either a Circe encoder or decoder for ADT尝试为 ADT 编写 Circe 编码器或解码器时遇到错误
【发布时间】：2019-04-14 16:58:46
【问题描述】：

我正在尝试基于Circe's documentation 编写一些代码，但是，尝试同时编译我的编码器和解码器会导致错误。

如果你想看看整个项目，你可以在 github (link to the file I have issues with) 上这样做

解码器

尝试编译以下代码：

package model

import java.time.LocalDateTime

import cats.effect.IO
import cats.syntax.functor._
import io.circe.generic.auto._
import io.circe.syntax._
import io.circe.{Decoder, Encoder}
import org.http4s.EntityDecoder
import org.http4s.circe.jsonOf

package object account {

  sealed trait AccountStatus
  case object Onboarding       extends AccountStatus
  case object SubmissionFailed extends AccountStatus
  case object Submitted        extends AccountStatus
  case object AccountUpdated   extends AccountStatus
  case object ApprovalPending  extends AccountStatus
  case object Active           extends AccountStatus
  case object Rejected         extends AccountStatus

  object AccountStatus {

    implicit val accountStatusEncoder: Encoder[AccountStatus] = Encoder.instance {
      case onboarding@Onboarding => onboarding.asJson
      case submissionFailed@SubmissionFailed => submissionFailed.asJson
      case submitted@Submitted => submitted.asJson
      case accountUpdated@AccountUpdated => accountUpdated.asJson
      case approvalPending@ApprovalPending => approvalPending.asJson
      case active@Active => active.asJson
      case rejected@Rejected => rejected.asJson
    }

    implicit val accountStatusDecoder: Decoder[AccountStatus] =
      List[Decoder[AccountStatus]](
        Decoder[Onboarding].widen,
        Decoder[SubmissionFailed].widen,
        Decoder[Submitted].widen,
        Decoder[AccountUpdated].widen,
        Decoder[ApprovalPending].widen,
        Decoder[Active].widen,
        Decoder[Rejected].widen
      ).reduceLeft(_ or _)

    implicit val AccountStatusEntityDecoder = jsonOf[IO, AccountStatus]

  }


  case class Account(
                      id: String,
                      status: AccountStatus,
                      currency: String,
                      buyingPower: Double,
                      cash: Double,
                      cashWithdrawable: Double,
                      portfolioValue: Double,
                      patternDayTrader: Boolean,
                      tradingBlocked: Boolean,
                      transfersBlocked: Boolean,
                      accountBlocked: Boolean,
                      createdAt: LocalDateTime
                    )

  object Account {
    implicit val AccountDecoder: EntityDecoder[IO, Account] = jsonOf[IO, Account]
  }

}

导致以下错误：

[error] /home/tom/code/scalpaca/src/main/scala/model/account.scala:38:19: not found: type Onboarding
[error]           Decoder[Onboarding].widen,
[error]                   ^
[error] /home/tom/code/scalpaca/src/main/scala/model/account.scala:39:19: not found: type SubmissionFailed
[error]           Decoder[SubmissionFailed].widen,
[error]                   ^
[error] /home/tom/code/scalpaca/src/main/scala/model/account.scala:40:19: not found: type Submitted
[error]           Decoder[Submitted].widen,
[error]                   ^
[error] /home/tom/code/scalpaca/src/main/scala/model/account.scala:41:19: not found: type AccountUpdated
[error]           Decoder[AccountUpdated].widen,
[error]                   ^
[error] /home/tom/code/scalpaca/src/main/scala/model/account.scala:42:19: not found: type ApprovalPending
[error]           Decoder[ApprovalPending].widen,
[error]                   ^
[error] /home/tom/code/scalpaca/src/main/scala/model/account.scala:43:19: not found: type Active
[error]           Decoder[Active].widen,
[error]                   ^
[error] /home/tom/code/scalpaca/src/main/scala/model/account.scala:44:19: not found: type Rejected
[error]           Decoder[Rejected].widen
[error]                   ^
[error] 7 errors found

我觉得这相当令人困惑，因为编译器所抱怨的类型在范围内非常明确，至少据我所知。

编码器

删除解码器、依赖它的 AccountStatusEntityDecoder 和 account 中的 AccountStatus 字段，留下以下内容

package model

import java.time.LocalDateTime

import cats.effect.IO
import cats.syntax.functor._
import io.circe.generic.auto._
import io.circe.syntax._
import io.circe.{Decoder, Encoder}
import org.http4s.EntityDecoder
import org.http4s.circe.jsonOf

package object account {

  sealed trait AccountStatus
  case object Onboarding       extends AccountStatus
  case object SubmissionFailed extends AccountStatus
  case object Submitted        extends AccountStatus
  case object AccountUpdated   extends AccountStatus
  case object ApprovalPending  extends AccountStatus
  case object Active           extends AccountStatus
  case object Rejected         extends AccountStatus

  object AccountStatus {

    implicit val accountStatusEncoder: Encoder[AccountStatus] = Encoder.instance {
      case onboarding@Onboarding => onboarding.asJson
      case submissionFailed@SubmissionFailed => submissionFailed.asJson
      case submitted@Submitted => submitted.asJson
      case accountUpdated@AccountUpdated => accountUpdated.asJson
      case approvalPending@ApprovalPending => approvalPending.asJson
      case active@Active => active.asJson
      case rejected@Rejected => rejected.asJson
    }

  }

  case class Account(
                      id: String,
                      currency: String,
                      buyingPower: Double,
                      cash: Double,
                      cashWithdrawable: Double,
                      portfolioValue: Double,
                      patternDayTrader: Boolean,
                      tradingBlocked: Boolean,
                      transfersBlocked: Boolean,
                      accountBlocked: Boolean,
                      createdAt: LocalDateTime
                    )

  object Account {
    implicit val AccountDecoder: EntityDecoder[IO, Account] = jsonOf[IO, Account]
  }

}

我再次收到一些警告和错误：

[info] Compiling 1 Scala source to /home/tom/code/scalpaca/target/scala-2.12/classes ...
[warn] /home/tom/code/scalpaca/src/main/scala/model/account.scala:27:48: match may not be exhaustive.
[warn] It would fail on the following input: Onboarding
[warn]       case onboarding@Onboarding => onboarding.asJson
[warn]                                                ^
[warn] /home/tom/code/scalpaca/src/main/scala/model/account.scala:28:66: match may not be exhaustive.
[warn] It would fail on the following input: SubmissionFailed
[warn]       case submissionFailed@SubmissionFailed => submissionFailed.asJson
[warn]                                                                  ^
[warn] /home/tom/code/scalpaca/src/main/scala/model/account.scala:29:45: match may not be exhaustive.
[warn] It would fail on the following input: Submitted
[warn]       case submitted@Submitted => submitted.asJson
[warn]                                             ^
[warn] /home/tom/code/scalpaca/src/main/scala/model/account.scala:30:60: match may not be exhaustive.
[warn] It would fail on the following input: AccountUpdated
[warn]       case accountUpdated@AccountUpdated => accountUpdated.asJson
[warn]                                                            ^
[warn] /home/tom/code/scalpaca/src/main/scala/model/account.scala:31:63: match may not be exhaustive.
[warn] It would fail on the following input: ApprovalPending
[warn]       case approvalPending@ApprovalPending => approvalPending.asJson
[warn]                                                               ^
[warn] /home/tom/code/scalpaca/src/main/scala/model/account.scala:32:36: match may not be exhaustive.
[warn] It would fail on the following input: Active
[warn]       case active@Active => active.asJson
[warn]                                    ^
[warn] /home/tom/code/scalpaca/src/main/scala/model/account.scala:33:42: match may not be exhaustive.
[warn] It would fail on the following input: Rejected
[warn]       case rejected@Rejected => rejected.asJson
[warn]                                          ^
[error] Error while emitting account.scala
[error] assertion failed: 
[error]   Cannot emit primitive conversion from Lmodel/account/package$AccountStatus; to Lmodel/account/package$Onboarding$; - account.scala
[error]      while compiling: /home/tom/code/scalpaca/src/main/scala/model/account.scala
[error]         during phase: jvm
[error]      library version: version 2.12.8
[error]     compiler version: version 2.12.8
[error]   reconstructed args: -bootclasspath /home/tom/jdk1.8.0_201/jre/lib/resources.jar:/home/tom/jdk1.8.0_201/jre/lib/rt.jar:/home/tom/jdk1.8.0_201/jre/lib/sunrsasign.jar:/home/tom/jdk1.8.0_201/jre/lib/jsse.jar:/home/tom/jdk1.8.0_201/jre/lib/jce.jar:/home/tom/jdk1.8.0_201/jre/lib/charsets.jar:/home/tom/jdk1.8.0_201/jre/lib/jfr.jar:/home/tom/jdk1.8.0_201/jre/classes:/home/tom/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.12.8.jar -Ypartial-unification -classpath /home/tom/code/scalpaca/target/scala-2.12/classes:/home/tom/.ivy2/cache/io.circe/circe-generic_2.12/jars/circe-generic_2.12-0.11.1.jar:/home/tom/.ivy2/cache/io.circe/circe-parser_2.12/jars/circe-parser_2.12-0.11.1.jar:/home/tom/.ivy2/cache/io.circe/circe-java8_2.12/jars/circe-java8_2.12-0.11.1.jar:/home/tom/.ivy2/cache/org.http4s/http4s-circe_2.12/jars/http4s-circe_2.12-0.20.0-M4.jar:/home/tom/.ivy2/cache/org.http4s/http4s-dsl_2.12/jars/http4s-dsl_2.12-0.20.0-M4.jar:/home/tom/.ivy2/cache/org.http4s/http4s-blaze-client_2.12/jars/http4s-blaze-client_2.12-0.20.0-M4.jar:/home/tom/.ivy2/cache/com.chuusai/shapeless_2.12/bundles/shapeless_2.12-2.3.3.jar:/home/tom/.ivy2/cache/io.circe/circe-jawn_2.12/jars/circe-jawn_2.12-0.11.1.jar:/home/tom/.ivy2/cache/org.http4s/http4s-jawn_2.12/jars/http4s-jawn_2.12-0.20.0-M4.jar:/home/tom/.ivy2/cache/org.http4s/http4s-client_2.12/jars/http4s-client_2.12-0.20.0-M4.jar:/home/tom/.ivy2/cache/org.http4s/http4s-blaze-core_2.12/jars/http4s-blaze-core_2.12-0.20.0-M4.jar:/home/tom/.ivy2/cache/io.circe/circe-core_2.12/jars/circe-core_2.12-0.11.1.jar:/home/tom/.ivy2/cache/org.typelevel/macro-compat_2.12/jars/macro-compat_2.12-1.1.1.jar:/home/tom/.ivy2/cache/org.typelevel/jawn-parser_2.12/jars/jawn-parser_2.12-0.14.1.jar:/home/tom/.ivy2/cache/org.http4s/jawn-fs2_2.12/jars/jawn-fs2_2.12-0.13.0.jar:/home/tom/.ivy2/cache/org.http4s/http4s-core_2.12/jars/http4s-core_2.12-0.20.0-M4.jar:/home/tom/.ivy2/cache/org.http4s/blaze-http_2.12/jars/blaze-http_2.12-0.14.0-M11.jar:/home/tom/.ivy2/cache/io.circe/circe-numbers_2.12/jars/circe-numbers_2.12-0.11.1.jar:/home/tom/.ivy2/cache/org.spire-math/jawn-parser_2.12/jars/jawn-parser_2.12-0.13.0.jar:/home/tom/.ivy2/cache/org.http4s/parboiled_2.12/jars/parboiled_2.12-1.0.0.jar:/home/tom/.ivy2/cache/co.fs2/fs2-io_2.12/jars/fs2-io_2.12-1.0.2.jar:/home/tom/.ivy2/cache/org.eclipse.jetty.alpn/alpn-api/jars/alpn-api-1.1.3.v20160715.jar:/home/tom/.ivy2/cache/com.twitter/hpack/jars/hpack-1.0.2.jar:/home/tom/.ivy2/cache/org.http4s/blaze-core_2.12/jars/blaze-core_2.12-0.14.0-M11.jar:/home/tom/.ivy2/cache/org.log4s/log4s_2.12/jars/log4s_2.12-1.6.1.jar:/home/tom/.ivy2/cache/co.fs2/fs2-core_2.12/jars/fs2-core_2.12-1.0.2.jar:/home/tom/.ivy2/cache/org.typelevel/cats-effect_2.12/jars/cats-effect_2.12-1.1.0.jar:/home/tom/.ivy2/cache/org.slf4j/slf4j-api/jars/slf4j-api-1.7.25.jar:/home/tom/.ivy2/cache/org.scodec/scodec-bits_2.12/jars/scodec-bits_2.12-1.1.7.jar:/home/tom/.ivy2/cache/org.typelevel/cats-core_2.12/jars/cats-core_2.12-1.5.0.jar:/home/tom/.ivy2/cache/org.typelevel/cats-kernel_2.12/jars/cats-kernel_2.12-1.5.0.jar:/home/tom/.ivy2/cache/org.typelevel/cats-macros_2.12/jars/cats-macros_2.12-1.5.0.jar:/home/tom/.ivy2/cache/org.typelevel/machinist_2.12/jars/machinist_2.12-0.6.6.jar:/home/tom/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.12.6.jar
[error] 
[error]   last tree to typer: TypeTree(trait Decoder)
[error]        tree position: line 53 of /home/tom/code/scalpaca/src/main/scala/model/account.scala
[error]             tree tpe: io.circe.Decoder
[error]               symbol: abstract trait Decoder in package circe
[error]    symbol definition: abstract trait Decoder extends Serializable (a ClassSymbol)
[error]       symbol package: io.circe
[error]        symbol owners: trait Decoder
[error]            call site: constructor package$Account$anon$importedDecoder$macro$28$1$anon$macro$25$1 in package account
[error] 
[error] == Source file context for tree position ==
[error] 
[error]     50                     )
[error]     51 
[error]     52   object Account {
[error]     53     implicit val AccountDecoder: EntityDecoder[IO, Account] = jsonOf[IO, Account]
[error]     54   }
[error]     55 
[error]     56 }
[error] Error while emitting account.scala
[error] assertion failed: Cannot emit primitive conversion from Lmodel/account/package$AccountStatus; to Lmodel/account/package$SubmissionFailed$; - account.scala
[error] Error while emitting account.scala
[error] assertion failed: Cannot emit primitive conversion from Lmodel/account/package$AccountStatus; to Lmodel/account/package$Submitted$; - account.scala
[error] Error while emitting account.scala
[error] assertion failed: Cannot emit primitive conversion from Lmodel/account/package$AccountStatus; to Lmodel/account/package$AccountUpdated$; - account.scala
[error] Error while emitting account.scala
[error] assertion failed: Cannot emit primitive conversion from Lmodel/account/package$AccountStatus; to Lmodel/account/package$ApprovalPending$; - account.scala
[error] Error while emitting account.scala
[error] assertion failed: Cannot emit primitive conversion from Lmodel/account/package$AccountStatus; to Lmodel/account/package$Active$; - account.scala
[error] Error while emitting account.scala
[error] assertion failed: Cannot emit primitive conversion from Lmodel/account/package$AccountStatus; to Lmodel/account/package$Rejected$; - account.scala
[warn] 7 warnings found
[error] 7 errors found

我无法弄清楚帐户为何受到影响。 如果我完全删除 AccountStatus 伴随对象，我的项目就会编译。

我希望得到一些帮助以消除这些错误，我们仍将不胜感激您的意见。谢谢

【问题讨论】：

  • 你必须将.type添加到隐式val accountStatusDecoder中的case对象：Decoder[AccountStatus] = List[Decoder[AccountStatus]]( Decoder[Onboarding.type].widen等

标签： scala circe


【解决方案1】：

为以后可能偶然发现此问题的人提供完整的答案：

stsatlantis 的建议确实解决了其中一个问题（感谢您的评论！），而另一个问题可以通过稍微修改 accountStatusEncoder 来解决。另一种解决方案是在您的 ADT 中使用案例类，但是，如果您已经有案例对象，那可能是因为它们更适合您的需求/领域。

我最终做出的改变：

  object AccountStatus {

  implicit val accountStatusEncoder: Encoder[AccountStatus] =
    Encoder.instance {
      status => status match {
          case Onboarding => status.asJson
          case SubmissionFailed => status.asJson
          case Submitted => status.asJson
          case AccountUpdated => status.asJson
          case ApprovalPending => status.asJson
          case Active => status.asJson
          case Rejected => status.asJson
      }
    }

  implicit val accountStatusDecoder: Decoder[AccountStatus] =
    List[Decoder[AccountStatus]](
      Decoder[Onboarding.type].widen,
      Decoder[SubmissionFailed.type].widen,
      Decoder[Submitted.type].widen,
      Decoder[AccountUpdated.type].widen,
      Decoder[ApprovalPending.type].widen,
      Decoder[Active.type].widen,
      Decoder[Rejected.type].widen
    ).reduceLeft(_ or _)

  implicit val AccountStatusEntityDecoder = jsonOf[IO, AccountStatus]
}

【讨论】：

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