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• InvertibleRemove.scala

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scodec.codecs.InvertibleRemove.scala Maven / Gradle / Ivy

package scodec
package codecs

import shapeless._

/** Similar to Shapeless's remove support for HLists but supports inverting the removal. */
sealed trait InvertibleRemove[L <: HList, A] {
  type Out <: HList
  def apply(l: L): Out
  def invert(out: Out, a: A): L
}

/** Companion for [[InvertibleRemove]]. */
object InvertibleRemove {
  type Aux[L0 <: HList, A0, Out0 <: HList] = InvertibleRemove[L0, A0] { type Out = Out0 }

  implicit def forTargetType[T <: HList, A]: InvertibleRemove.Aux[A :: T, A, T] =
    new InvertibleRemove[A :: T, A] {
      type Out = T
      def apply(in: A :: T): T = in.tail
      def invert(out: T, a: A): A :: T = a :: out
    }

  implicit def forNonTargetType[H, T <: HList, A](
    implicit rest: InvertibleRemove[T, A]
  ): InvertibleRemove.Aux[H :: T, A, H :: rest.Out] =
    new InvertibleRemove[H :: T, A] {
      type Out = H :: rest.Out
      def apply(l: H :: T): Out =
        l.head :: rest(l.tail)
      def invert(out: H :: rest.Out, a: A): H :: T =
        out.head :: rest.invert(out.tail, a)
    }
}