//arrow-optics/arrow.optics/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

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 |

Name | Summary |
---|---|

Companion | common object Companion |

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 |

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 |

Name |
---|

PIso |

PLens |

PPrism |

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