ImplicitBijection.scala

package com.twitter.bijection

/** Deals with the type-system issue around resolving implicit bijections.
 * Bijection[A,B] or Bijection[B,A], which should
 * be equivalent. Only use this type as an implicit parameter.
 */
import scala.annotation.implicitNotFound
@implicitNotFound(msg = "Cannot find ImplicitBijection type class from ${A} to ${B}")
sealed trait ImplicitBijection[A, B] extends (A => B) with java.io.Serializable {
  def bijection: Bijection[A, B]
  def apply(a: A) = bijection.apply(a)
  def invert(b: B) = bijection.invert(b)
}
case class Forward[A, B](override val bijection: Bijection[A,B]) extends ImplicitBijection[A, B]
case class Reverse[A, B](inv: Bijection[B, A]) extends ImplicitBijection[A, B] {
  lazy val bijection = inv.inverse
}

trait LowPriorityImplicitBijection extends java.io.Serializable {
  implicit def reverse[A, B](implicit bij: Bijection[B, A]): ImplicitBijection[A, B] = Reverse(bij)
}

object ImplicitBijection extends LowPriorityImplicitBijection {
  implicit def forward[A, B](implicit bij: Bijection[A, B]): ImplicitBijection[A, B] = Forward(bij)
}