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monocle

Optional

object Optional

Source
Optional.scala
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Value Members

  1. def apply[S, A](_getOption: (S) => Option[A])(_set: (A) => (S) => S): Optional[S, A]

    alias for POptional apply restricted to monomorphic update

  2. def filter[A](predicate: (A) => Boolean): Optional[A, A]

    Select all the elements which satisfies the predicate.

    Select all the elements which satisfies the predicate.

    val positiveNumbers = Traversal.fromTraverse[List, Int] composeOptional filter[Int](_ >= 0)

positiveNumbers.getAll(List(1,2,-3,4,-5)) == List(1,2,4)
positiveNumbers.modify(_ * 10)(List(1,2,-3,4,-5)) == List(10,20,-3,40,-5)

    filter can break the fusion property, if replace or modify do not preserve the predicate. For example, here the first modify (x - 3) transform the positive number 1 into the negative number -2.

    val positiveNumbers = Traversal.fromTraverse[List, Int] composeOptional Optional.filter[Int](_ >= 0)
val list            = List(1, 5, -3)
val firstStep       = positiveNumbers.modify(_ - 3)(list)            // List(-2, 2, -3)
val secondStep      = positiveNumbers.modify(_ * 2)(firstStep)       // List(-2, 4, -3)
val bothSteps       = positiveNumbers.modify(x => (x - 3) * 2)(list) // List(-4, 4, -3)
secondStep != bothSteps
    See also

    This method is called filtered in Haskell Lens.

  3. def void[S, A]: Optional[S, A]

    Optional that points to nothing

Deprecated Value Members

  1. def codiagonal[S]: Optional[Either[S, S], S]
    Annotations
    @deprecated
    Deprecated

    (Since version 3.0.0-M4) use Lens.codiagonal

  2. def id[A]: Optional[A, A]
    Annotations
    @deprecated
    Deprecated

    (Since version 3.0.0-M2) use Iso.id