//arrow-optics/arrow.optics/Fold

A Fold is an optic that allows to focus into structure and get multiple results.

Fold is a generalisation of an instance of Foldable and is implemented in terms of foldMap.

common

S | the source of a Fold |

A | the target of a Fold |

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 |

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 |

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. |

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 abstract 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 |

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 |

plus | common open operator fun <C> plus(other: Fold<in A, out C>): Fold<S, C> |

right | common open fun <C> right(): Fold<Either<C, S>, Either<C, A» Create a sum of a type C and the Fold |

size | common open fun size(source: S): Int Calculate the number of targets |

Name |
---|

PEvery |

Getter |

PIso |

PLens |

POptional |

PPrism |

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

at | common fun <T, S, I, A> Fold<T, S>.at(AT: At<S, I, A>, i: I): Fold<T, A> DSL to compose At with a Fold for a structure S to focus in on A at given index I. |

every | common fun <T, S, A> Fold<T, S>.every(TR: Every<S, A>): Fold<T, A> DSL to compose Traversal with a Fold for a structure S to see all its foci A |

index | common fun <T, S, I, A> Fold<T, S>.index(ID: Index<S, I, A>, i: I): Fold<T, A> DSL to compose Index with a Fold for a structure S to focus in on A at given index I |

some | common val <T, S> Fold<T, Option<S».some: Fold<T, S> DSL to compose a Prism with focus arrow.core.Some with a Fold with a focus of Option<S> |

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