TypeclassBijection.scala

// in bijection branch jco/macro_case_class_plus
// ./sbt "bijection-macros/console"
// paste the following

// Use :paste until the break below.
:paste
import com.twitter.bijection._
import com.twitter.bijection.macros.common.TypesNotEqual

trait Semigroup[T] {
  def plus(left: T, right: T): T
}

implicit val intSemigroup: Semigroup[Int] = new Semigroup[Int] {
  override def plus(left: Int, right: Int) = left + right
}

case class Wrapper(get: Int) extends AnyVal

implicit val intWrapperBij: Bijection[Int, Wrapper] = Bijection.build[Int, Wrapper] { Wrapper(_) } { _.get }

trait TypeclassBijection[T[_]] {
  def apply[A, B](tc: T[A], bij: Bijection[A, B]): T[B]
}

implicit val semigroupTypeclassBijection: TypeclassBijection[Semigroup] = new TypeclassBijection[Semigroup] {
  def apply[A, B](tc: Semigroup[A], bij: Bijection[A, B]) =
    new Semigroup[B] {
      override def plus(left: B, right: B) = bij(tc.plus(bij.invert(left), bij.invert(right)))
    }
}

// Now hit Ctrl-D and paste the rest.

import com.twitter.bijection.macros.common.MacroImplicits._

implicit def typeclassBijection[T[_], A, B](implicit tcBij: TypeclassBijection[T], typeclass: T[A], notEqual: TypesNotEqual[A, B], bij: ImplicitBijection[A, B]): T[B] = tcBij(typeclass, bij.bijection)

implicitly[Semigroup[Wrapper]]