CU-fh2vcf - Deprecate mapN and fix zip for collections #2324
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aballano
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Mar 11, 2021
arrow-libs/core/arrow-core-data/src/main/kotlin/arrow/core/NonEmptyList.kt
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aballano
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arrow-libs/core/arrow-core-data/src/main/kotlin/arrow/core/NonEmptyList.kt
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nomisRev
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Mar 12, 2021
arrow-libs/core/arrow-core-data/src/main/kotlin/arrow/core/NonEmptyList.kt
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arrow-libs/core/arrow-core-data/src/main/kotlin/arrow/core/NonEmptyList.kt
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nomisRev
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nomisRev
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| val bb = iterator() | ||
| val cc = c.iterator() | ||
| val dd = d.iterator() | ||
|
|
||
| val size = minOf( | ||
| collectionSizeOrDefault(10), | ||
| c.collectionSizeOrDefault(10), | ||
| d.collectionSizeOrDefault(10) | ||
| ) | ||
| val list = ArrayList<E>(size) | ||
| while (bb.hasNext() && cc.hasNext() && dd.hasNext()) { | ||
| list.add(transform(bb.next(), cc.next(), dd.next())) | ||
| } | ||
| return list |
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This impl was inspired by the Kotlin Std implementation
aballano
approved these changes
Mar 12, 2021
| "zip2" { | ||
| forAll(Gen.nonEmptyList(Gen.int()), Gen.nonEmptyList(Gen.int())) { a, b -> | ||
| val result = a.zip(b) | ||
| val expected = a.all.zip(b.all).let(NonEmptyList.Companion::fromListUnsafe) |
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aren't we testing against our own zip version here?
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Yes, but that zip is tested against Kotlin Std zip in IterableTest so it assumes our zip is correct/tested. Which is added in this PR also.
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Worked on this PR after requesting changes so dismissing my review.
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This PR updates/fixes some
zipimplementations and adds tests for it.It also deprecates
mapNfor collections, which were cartesian builders. For collections, this easily results in really big lists that make the JVM OOM.Example of dangerous usage:
This tries to create a list with 6^10 (60466176) elements and as a result OOMs. As you can see this easily results in bad code since here we're only using a list with 6 elements and it already results in problematic code.
Since this pattern isn't so common and is only safe with low arities we will recommend to simply use
flatMap/mapchains instead.