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71 changes: 71 additions & 0 deletions
71
arrow-libs/optics/arrow-optics/src/commonMain/kotlin/arrow/optics/Delicate.kt
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|---|---|---|
| @@ -0,0 +1,71 @@ | ||
| package arrow.optics | ||
|
|
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| import arrow.core.None | ||
| import arrow.core.Some | ||
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| @RequiresOptIn( | ||
| level = RequiresOptIn.Level.WARNING, | ||
| message = "Delicate optic, please check the documentation for correct usage." | ||
| ) | ||
| @Retention(AnnotationRetention.BINARY) | ||
| @Target(AnnotationTarget.FUNCTION) | ||
| public annotation class DelicateOptic | ||
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| /** | ||
| * Focuses on the value only if the [predicate] is true. | ||
| * This optics The optic is perfectly OK when used to get | ||
| * values using `getOrNull` or `getAll`; but requires | ||
| * some caution using `modify` with it. | ||
| * | ||
| * ⚠️ Warning: when using `modify` with this optic, | ||
| * the transformation should not alter the values that are | ||
| * taken into account by the predicate. For example, it is | ||
| * fine to `filter` by `name` and then increase the `age`, | ||
| * but not to `filter` by `name` and then capitalize the `name`. | ||
| * | ||
| * In general terms, this optic does not satisfy the rule that | ||
| * applying two modifications in a row is equivalent to | ||
| * applying those two modifications at once. The following | ||
| * example shows that increasing by one twice is not equivalent | ||
| * to increasing by two. | ||
| * | ||
| * ``` | ||
| * val p = Optional.filter<Int> { it % 2 == 0 } // focus on even numbers | ||
| * val n = 2 // an even number | ||
| * | ||
| * p.modify(p.modify(n) { it + 1 }) { it + 1 } | ||
| * // ---------------------- = 3 | ||
| * // ---------------------------------------- = null | ||
| * | ||
| * p.modify(n) { it + 2 } | ||
| * // ------------------- = 4 | ||
| * ``` | ||
| * | ||
| * The reader interested in a (deep) discussion about why | ||
| * this rule is important may consult the blog post | ||
| * [_Finding (correct) lens laws_](https://oleg.fi/gists/posts/2018-12-12-find-correct-laws.html) | ||
| * by Oleg Genrus. | ||
| */ | ||
| @DelicateOptic | ||
| public fun <S> POptional.Companion.filter( | ||
| predicate: (S) -> Boolean | ||
| ): Optional<S, S> = Optional( | ||
| getOption = { if (predicate(it)) Some(it) else None }, | ||
| set = { s, x -> if (predicate(s)) x else s } | ||
| ) | ||
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| /** | ||
| * Focuses on a sequence of lenses. | ||
| * | ||
| * Warning: using a lens more than once in the list | ||
| * may give unexpected results upon modification. | ||
| */ | ||
| @DelicateOptic | ||
| public fun <S, A, B> PTraversal.Companion.fromLenses( | ||
| lens1: PLens<S, S, A, B>, vararg lenses: PLens<S, S, A, B> | ||
| ): PTraversal<S, S, A, B> = object : PTraversal<S, S, A, B> { | ||
| override fun <R> foldMap(initial: R, combine: (R, R) -> R, source: S, map: (focus: A) -> R): R = | ||
| lenses.fold(map(lens1.get(source))) { current, lens -> combine(current, map(lens.get(source))) } | ||
| override fun modify(source: S, map: (focus: A) -> B): S = | ||
| lenses.fold(lens1.modify(source, map)) { current, lens -> lens.modify(current, map) } | ||
| } |
28 changes: 28 additions & 0 deletions
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arrow-libs/optics/arrow-optics/src/commonMain/kotlin/arrow/optics/dsl/delicate.kt
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,28 @@ | ||
| package arrow.optics.dsl | ||
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| import arrow.optics.DelicateOptic | ||
| import arrow.optics.Optional | ||
| import arrow.optics.Traversal | ||
| import arrow.optics.filter | ||
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| /** | ||
| * Focuses on those values for which the [predicate] is true. | ||
| * | ||
| * See [Optional.filter] for further description of the | ||
| * caution one should be with this optic. | ||
| */ | ||
| @DelicateOptic | ||
| public fun <S, A> Traversal<S, A>.filter( | ||
| predicate: (A) -> Boolean | ||
| ): Traversal<S, A> = this compose Optional.filter(predicate) | ||
|
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| /** | ||
| * Focuses on the value only if the [predicate] is true. | ||
| * | ||
| * See [Optional.filter] for further description of the | ||
| * caution one should be with this optic. | ||
| */ | ||
| @DelicateOptic | ||
| public fun <S, A> Optional<S, A>.filter( | ||
| predicate: (A) -> Boolean | ||
| ): Optional<S, A> = this compose Optional.filter(predicate) |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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|
@@ -205,5 +205,4 @@ class PrismTest { | |
| Prism.sumType().all(sum) { predicate } shouldBe (predicate || sum is SumType.B) | ||
| } | ||
| } | ||
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| } | ||