cats.Inject.scala Maven / Gradle / Ivy
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package cats
/**
* Inject is a type class providing an injection from type `A` into
* type `B`. An injection is a function `inj` which does not destroy
* any information: for every `b: B` there is at most one `a: A` such
* that `inj(a) = b`.
*
* Because of this all injections admit partial inverses `prj` which
* pair a value `b: B` back with a single value `a: A`.
*
* @since 1.0
* @note Prior to cats 1.0, Inject handled injection for type
* constructors. For injection of type constructors, use [[InjectK]].
*
* @see [[InjectK]] for injection for [[cats.data.EitherK]]
*/
abstract class Inject[A, B] {
def inj: A => B
def prj: B => Option[A]
final def apply(a: A): B = inj(a)
final def unapply(b: B): Option[A] = prj(b)
}
sealed abstract private[cats] class InjectInstances {
implicit def catsReflexiveInjectInstance[A]: Inject[A, A] =
new Inject[A, A] {
val inj = identity(_: A)
val prj = Some(_: A)
}
implicit def catsLeftInjectInstance[A, B]: Inject[A, Either[A, B]] =
new Inject[A, Either[A, B]] {
val inj = Left(_: A)
val prj = (_: Either[A, B]).left.toOption
}
implicit def catsRightInjectInstance[A, B, C](implicit I: Inject[A, B]): Inject[A, Either[C, B]] =
new Inject[A, Either[C, B]] {
val inj = (a: A) => Right(I.inj(a))
val prj = (_: Either[C, B]).toOption.flatMap(I.prj)
}
}
object Inject extends InjectInstances {
def apply[A, B](implicit I: Inject[A, B]): Inject[A, B] = I
}