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Added contravariant instance for ConfigDecoder #514

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merged 4 commits into from
Oct 17, 2021
Merged

Added contravariant instance for ConfigDecoder #514

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dc2fbd5
Added contravariant instance for ConfigDecoder
dimitarg Oct 14, 2021
ae0a9cc
Cleanup
vlovgr Oct 17, 2021
fa11665
Organize imports
vlovgr Oct 17, 2021
46cf6ad
Add ConfigDecoder#contramap
vlovgr Oct 17, 2021
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20 changes: 19 additions & 1 deletion modules/core/src/main/scala/ciris/ConfigDecoder.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@

package ciris

import cats.{MonadError, Show}
import cats.{Contravariant, MonadError, Show}
import cats.implicits._
import scala.annotation.tailrec
import scala.concurrent.duration.{Duration, FiniteDuration}
Expand Down Expand Up @@ -40,6 +40,13 @@ sealed abstract class ConfigDecoder[A, B] {
}
}

/**
* Returns a new [[ConfigDecoder]] which applies the
* specified function on the value before decoding.
*/
final def contramap[C](f: C => A): ConfigDecoder[C, B] =
ConfigDecoder.instance { (key, value) => decode(key, f(value)) }

/**
* Attempts to decode the specified value to the second type.
*
Expand Down Expand Up @@ -329,6 +336,17 @@ object ConfigDecoder {
}
}

/**
* @group Instances
*/
implicit final def configDecoderContravariant[B]: Contravariant[ConfigDecoder[*, B]] =
new Contravariant[ConfigDecoder[*, B]] {
override final def contramap[A, C](decoder: ConfigDecoder[A, B])(
f: C => A
): ConfigDecoder[C, B] =
decoder.contramap(f)
}

/**
* @group Instances
*/
Expand Down
6 changes: 6 additions & 0 deletions modules/core/src/test/scala/ciris/ConfigDecoderSpec.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@ package ciris

import cats.data.Chain
import cats.implicits._
import cats.laws.discipline.ContravariantTests
import cats.laws.discipline.MonadErrorTests
import org.scalacheck.Gen
import scala.concurrent.duration.{Duration, FiniteDuration}
Expand Down Expand Up @@ -215,6 +216,11 @@ final class ConfigDecoderSpec extends BaseSpec {
}
}

checkAll(
"ConfigDecoder",
ContravariantTests[ConfigDecoder[*, String]].contravariant[String, String, String]
)

checkAll(
"ConfigDecoder",
MonadErrorTests[ConfigDecoder[String, *], ConfigError].monadError[String, String, String]
Expand Down