Aligning coproduct types

gistfile1.txt

package scodec

import shapeless._
import shapeless.ops.coproduct._

object CoproductOps {

  sealed trait Align[A <: Coproduct, B <: Coproduct] {
    def apply(a: A): B
  }

  object Align {
    implicit def cnilAlign: Align[CNil, CNil] = new Align[CNil, CNil] {
      def apply(cn: CNil) = cn
    }

    implicit def coproductAlign[A <: Coproduct, BH, BT <: Coproduct, R <: Coproduct](implicit
      remove: Remove.Aux[A, BH, R], alignTail: Align[R, BT]
    ): Align[A, BH :+: BT] = new Align[A, BH :+: BT] {
      def apply(a: A) = remove(a) match {
        case Left(bh) => Inl(bh)
        case Right(rest) => Inr(alignTail(rest))
      }
    }
  }

  implicit class AlignSyntax[C <: Coproduct](val self: C) extends AnyVal {
    def align[To <: Coproduct](implicit align: Align[C, To]): To = align(self)
  }
}