Transform an F[A]
into an F[B]
by providing a transformation from A
to B
and one from B
to A
.
Transform an F[A]
into an F[B]
by providing a transformation from A
to B
and one from B
to A
.
Example:
scala> import cats.implicits._ scala> import scala.concurrent.duration._ scala> val durSemigroup: Semigroup[FiniteDuration] = | Invariant[Semigroup].imap(Semigroup[Long])(Duration.fromNanos)(_.toNanos) scala> durSemigroup.combine(2.seconds, 3.seconds) res1: FiniteDuration = 5 seconds
Lifts natural subtyping contravariance of contravariant Functors.
Lifts natural subtyping contravariance of contravariant Functors. could be implemented as contramap(identity), but the Functor laws say this is equivalent
Must obey the laws defined in cats.laws.ContravariantLaws.