Packages

trait Contravariant[F[_]] extends Invariant[F]

Must obey the laws defined in cats.laws.ContravariantLaws.

Self Type
Contravariant[F]
Source
Contravariant.scala
Linear Supertypes
Invariant[F], Serializable, Serializable, AnyRef, Any
Known Subclasses
ContravariantMonoidal, ContravariantSemigroupal
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Inherited
  1. Contravariant
  2. Invariant
  3. Serializable
  4. Serializable
  5. AnyRef
  6. Any
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Visibility
  1. Public
  2. All

Abstract Value Members

  1. abstract def contramap[A, B](fa: F[A])(f: (B) ⇒ A): F[B]

Concrete Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  4. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  5. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
  6. def compose[G[_]](implicit arg0: Contravariant[G]): Functor[[α]F[G[α]]]
  7. def compose[G[_]](implicit arg0: Invariant[G]): Invariant[[α]F[G[α]]]

    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.syntax.all._
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)
    Definition Classes
    Invariant
  8. def composeContravariant[G[_]](implicit arg0: Contravariant[G]): Invariant[[α]F[G[α]]]

    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.syntax.all._
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
    Definition Classes
    Invariant
  9. def composeFunctor[G[_]](implicit arg0: Functor[G]): Contravariant[[α]F[G[α]]]

    Compose Invariant F[_] and Functor G[_] then produce Invariant[F[G[_]]] using F's imap and G's map.

    Compose Invariant F[_] and Functor G[_] then produce Invariant[F[G[_]]] using F's imap and G's map.

    Example:

    scala> import cats.syntax.all._
scala> import scala.concurrent.duration._

scala> val durSemigroupList: Semigroup[List[FiniteDuration]] =
     | Invariant[Semigroup]
     |   .composeFunctor[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)
    Definition Classes
    Contravariant → Invariant
  10. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  11. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  12. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
  13. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  14. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  15. def imap[A, B](fa: F[A])(f: (A) ⇒ B)(fi: (B) ⇒ A): F[B]

    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.syntax.all._
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
    Definition Classes
    Contravariant → Invariant
  16. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  17. def liftContravariant[A, B](f: (A) ⇒ B): (F[B]) ⇒ F[A]
  18. def narrow[A, B <: A](fa: F[A]): F[B]

    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

  19. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  20. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  21. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  22. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  23. def toString(): String
    Definition Classes
    AnyRef → Any
  24. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  25. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  26. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()

Inherited from Invariant[F]

Inherited from Serializable

Inherited from Serializable

Inherited from AnyRef

Inherited from Any

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