Must obey the laws defined in cats.laws.ContravariantLaws.
- Companion:
- object
Value members
Concrete methods
Lifts natural subtyping contravariance of contravariant Functors. could be implemented as contramap(identity), but the Functor laws say this is equivalent
Lifts natural subtyping contravariance of contravariant Functors. could be implemented as contramap(identity), but the Functor laws say this is equivalent
Inherited methods
Compose Invariant F[_] and G[_] then produce Invariant[F[G[_]]] using their imap.
Compose Invariant F[_] and G[_] then produce Invariant[F[G[_]]] using their imap.
Example:
scala> import cats.implicits._
scala> import scala.concurrent.duration._
scala> val durSemigroupList: Semigroup[List[FiniteDuration]] =
| Invariant[Semigroup].compose[List].imap(Semigroup[List[Long]])(Duration.fromNanos)(_.toNanos)
scala> durSemigroupList.combine(List(2.seconds, 3.seconds), List(4.seconds))
res1: List[FiniteDuration] = List(2 seconds, 3 seconds, 4 seconds)
- Inherited from:
- Invariant
Compose Invariant F[_] and Contravariant G[_] then produce Invariant[F[G[_]]]
using F's imap and G's contramap.
Compose Invariant F[_] and Contravariant G[_] then produce Invariant[F[G[_]]]
using F's imap and G's contramap.
Example:
scala> import cats.implicits._
scala> import scala.concurrent.duration._
scala> type ToInt[T] = T => Int
scala> val durSemigroupToInt: Semigroup[ToInt[FiniteDuration]] =
| Invariant[Semigroup]
| .composeContravariant[ToInt]
| .imap(Semigroup[ToInt[Long]])(Duration.fromNanos)(_.toNanos)
// semantically equal to (2.seconds.toSeconds.toInt + 1) + (2.seconds.toSeconds.toInt * 2) = 7
scala> durSemigroupToInt.combine(_.toSeconds.toInt + 1, _.toSeconds.toInt * 2)(2.seconds)
res1: Int = 7
- Inherited from:
- Invariant