类型不匹配;发现:猫.显示[无形.CNil]需要:猫.在 sbt 中添加 scalac 选项 -Ypart-unific

Question

我有以下代码。

import enumeratum.{Enum, EnumEntry}
sealed abstract class AppEnvironment extends EnumEntry
object AppEnvironment extends Enum[AppEnvironment] {
  case object Local extends AppEnvironment
  case object Testing extends AppEnvironment
  case object Production extends AppEnvironment
  override val values: Vector[AppEnvironment] =
    findValues.toVector
}
import java.net.InetAddress
import ciris.Secret
import eu.timepit.refined.types.net.UserPortNumber
import scala.concurrent.duration.Duration
final case class ApiConfig(
  host: InetAddress,
  port: UserPortNumber,
  apiKey: Secret[ApiKey],
  timeout: Duration
)

import java.net.InetAddress
import cats.Show
import cats.derived._
import cats.implicits._
import ciris.Secret
import ciris.cats._
import enumeratum.EnumEntry
import eu.timepit.refined.auto._
import eu.timepit.refined.cats._
import eu.timepit.refined.types.net.UserPortNumber
import eu.timepit.refined.types.string.NonEmptyString
import is.cir.example.domain.config.AppEnvironment.{Local, Production, Testing}
import scala.concurrent.duration._
final case class Config(
  appName: NonEmptyString,
  environment: AppEnvironment,
  api: ApiConfig
)

object Config {
  import cats.implicits._
  implicit val showConfig: Show[Config] = {
    implicit val showInetAddress: Show[InetAddress] =
      Show.fromToString
    implicit def showEnumEntry[E <: EnumEntry]: Show[E] =
      Show.show(_.entryName)
    semi.show
  }
}

我必须在build.sbt中添加-Ypartial-unification scalac选项以解决另一个问题，添加后我得到了另一个先前未发生的异常（没有标志）。

错误是——

[error] /Users/rajkumar.natarajan/Documents/Coding/OS/ciris-example/src/main/scala/is/cir/example/domain/config/Config.scala:38:10: type mismatch;
[error]  found   : cats.Show[shapeless.CNil]
[error]  required: cats.Show[is.cir.example.domain.config.Config]
[error]     semi.show
[error]          ^
[error] one error found

如何解决此错误？

Answer 1

你应该指定类型参数调用它

semi.show[Config]

至少错误消息是不同的

Error:(82, 14) diverging implicit expansion for type cats.derived.MkShow[is.cir.example.domain.config.Config]
starting with value tagRefType in object RefType
    semi.show[Config]

您可以尝试使用Show实例。为了对"较大"案例类进行Show，您应该为"较小"案例类Show。

implicitly[Show[Config]]
implicitly[Show[AppEnvironment]]
implicitly[Show[AppEnvironment.Local.type]]
//...
implicitly[Show[ApiConfig]]
implicitly[Show[InetAddress]]
//...