//arrow-optics/arrow.optics/POptional

POptional

common interface POptional<S, T, A, B> : PSetter<S, T, A, B> , Fold<S, A> , PTraversal<S, T, A, B> , PEvery<S, T, A, B>

Optional is an optic that allows to focus into a structure and querying or copy’ing an optional focus.

import arrow.core.None
import arrow.core.Option
import arrow.core.Some
import arrow.optics.Optional

data class User(val username: String, val email: Option<String>) {
    companion object {
      // can be out generated by @optics
      val email: Optional<User, String> = Optional(User::email) { user, email ->
        user.copy(email = Some(email))
      }
  }
}

fun main(args: Array<String>) {
  val original = User("arrow-user", None)
  val set = User.email.set(original, "arRoW-UsEr@arrow-Kt.IO")
  val modified = User.email.modify(set, String::toLowerCase)
  println("original: $original, set: $set, modified: $modified")
}

A (polymorphic) POptional is useful when setting or modifying a value for a type with a optional polymorphic focus i.e. POptional, Either, Int, String>

A POptional can be seen as a weaker Lens and Prism and combines their weakest functions:

  • set: (S, B) -> T meaning we can focus into an S and set a value B for a target A and obtain a modified source T
  • getOrModify: (S) -> Either<T, A> meaning it returns the focus of a POptional OR the original value

Parameters

common

   
S the source of a POptional
T the modified source of a POptional
A the focus of a POptional
B the modified focus of a POptional

Types

Name Summary
Companion common object Companion

Functions

Name Summary
all common open fun all(source: S, predicate: (A) -> Boolean): Boolean
Check if all targets satisfy the predicate
any common open fun any(source: S, predicate: (A) -> Boolean): Boolean
Returns true if at least one focus matches the given predicate.
choice common open infix fun <C> choice(other: Fold<C, A>): Fold<Either<S, C>, A>
Join two Fold with the same target
common open infix fun <S1, T1> choice(other: POptional<S1, T1, A, B>): POptional<Either<S, S1>, Either<T, T1>, A, B>
Join two POptional with the same focus B
common open infix fun <U, V> choice(other: PSetter<U, V, A, B>): PSetter<Either<S, U>, Either<T, V>, A, B>
Join two PSetter with the same target
common open fun <U, V> choice(other: PTraversal<U, V, A, B>): PTraversal<Either<S, U>, Either<T, V>, A, B>
combineAll common open fun combineAll(M: Monoid<A>, source: S): A
Alias for fold.
compose common open infix fun <C> compose(other: Fold<in A, out C>): Fold<S, C>
Compose a Fold with a Fold
common open infix fun <C, D> compose(other: PEvery<in A, out B, out C, in D>): PEvery<S, T, C, D>
Compose a PEvery with a PEvery
common open infix fun <C, D> compose(other: POptional<in A, out B, out C, in D>): POptional<S, T, C, D>
Compose a POptional with a POptional
common open infix fun <C, D> compose(other: PSetter<in A, out B, out C, in D>): PSetter<S, T, C, D>
Compose a PSetter with a PSetter
common open infix fun <C, D> compose(other: PTraversal<in A, out B, out C, in D>): PTraversal<S, T, C, D>
Compose a PTraversal with a PTraversal
exists common open fun exists(source: S, predicate: (A) -> Boolean): Boolean
Check whether at least one element satisfies the predicate.
findOrNull common open fun findOrNull(source: S, predicate: (A) -> Boolean): A?
Find the first element matching the predicate, if one exists.
first common open fun <C> first(): POptional<Pair<S, C>, Pair<T, C>, Pair<A, C>, Pair<B, C»
Create a product of the POptional and a type C
firstOrNull common open fun firstOrNull(source: S): A?
Get the first target or null
fold common open fun fold(M: Monoid<A>, source: S): A
Fold using the given Monoid instance.
foldMap common open override fun <R> foldMap(M: Monoid<R>, source: S, map: (A) -> R): R
Map each target to a type R and use a Monoid to fold the results
getAll common open fun getAll(source: S): List<A>
Get all targets of the Fold
getOrModify common abstract fun getOrModify(source: S): Either<T, A>
Get the focus of a POptional or return the original value while allowing the type to change if it does not match
getOrNull common open fun getOrNull(source: S): A?
Get the focus of a POptional or null if the is not there
isEmpty common open fun isEmpty(source: S): Boolean
Check if there is no target
isNotEmpty common open fun isNotEmpty(source: S): Boolean
Check if there is at least one target
lastOrNull common open fun lastOrNull(source: S): A?
Get the last target or null
left common open fun <C> left(): Fold<Either<S, C>, Either<A, C»
Create a sum of the Fold and a type C
lift common open fun lift(map: (A) -> B): (S) -> T
Lift a function map: (A) -> B to the context of S: (S) -> T`
modify common open override fun modify(source: S, map: (A) -> B): T
Modify the focus of a POptional with a function map
modifyNullable common open fun modifyNullable(source: S, map: (A) -> B): T?
Modify the focus of a POptional with a function map
plus common open operator fun <C> plus(other: Fold<in A, out C>): Fold<S, C>
open operator fun <C, D> plus(other: PEvery<in A, out B, out C, in D>): PEvery<S, T, C, D>
open operator fun <C, D> plus(other: POptional<in A, out B, out C, in D>): POptional<S, T, C, D>
open operator fun <C, D> plus(other: PSetter<in A, out B, out C, in D>): PSetter<S, T, C, D>
open operator fun <C, D> plus(other: PTraversal<in A, out B, out C, in D>): PTraversal<S, T, C, D>
right common open fun <C> right(): Fold<Either<C, S>, Either<C, A»
Create a sum of a type C and the Fold
second common open fun <C> second(): POptional<Pair<C, S>, Pair<C, T>, Pair<C, A>, Pair<C, B»
Create a product of a type C and the POptional
set common abstract override fun set(source: S, focus: B): T
Get the modified source of a POptional
setNullable common open fun setNullable(source: S, b: B): T?
Set the focus of a POptional with a value.
size common open fun size(source: S): Int
Calculate the number of targets

Properties

Name Summary
every common open val <U, V> PLens<U, V, S, T>.every: PTraversal<U, V, A, B>
DSL to compose Traversal with a Lens for a structure S to see all its foci A
every common open val <U, V> PIso<U, V, S, T>.every: PTraversal<U, V, A, B>
DSL to compose Traversal with a Iso for a structure S to see all its foci A
every common open val <U, V> PPrism<U, V, S, T>.every: PTraversal<U, V, A, B>
DSL to compose Traversal with a Prism for a structure S to see all its foci A
every common open val <U, V> POptional<U, V, S, T>.every: PTraversal<U, V, A, B>
DSL to compose Traversal with a Optional for a structure S to see all its foci A
every common open val <U, V> PSetter<U, V, S, T>.every: PSetter<U, V, A, B>
DSL to compose Traversal with a Setter for a structure S to see all its foci A
every common open val <U, V> PTraversal<U, V, S, T>.every: PTraversal<U, V, A, B>
DSL to compose Traversal with a Traversal for a structure S to see all its foci A
every common open val <U, V> PEvery<U, V, S, T>.every: PTraversal<U, V, A, B>
DSL to compose Traversal with a PEvery for a structure S to see all its foci A

Inheritors

Name
PIso
PLens
PPrism

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