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Fix LazyList.range [ci: last-only] #10767

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Fix LazyList.range [ci: last-only] #10767

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6de2bf8
Override LazyList.range
BalmungSan Apr 30, 2024
91088b5
Test LazyList.range
BalmungSan Apr 30, 2024
bd3db0d
Better LazyList.range impl
BalmungSan Apr 30, 2024
f7745a4
Move LazyList.range implementation closer to other overrides
BalmungSan Apr 30, 2024
2028dae
Ensure lazyness of `Integral[A].one` for overrided `range` implementa…
BalmungSan Apr 30, 2024
fbc2623
Ensure step can't be zero
BalmungSan Apr 30, 2024
1ac4f64
Allow reverse LazyList.range
BalmungSan Apr 30, 2024
b4eb90a
Make the lazyRangeAllowsMoreThanIntMaxValue test run fast
BalmungSan Apr 30, 2024
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7 changes: 7 additions & 0 deletions src/library/scala/collection/immutable/LazyList.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -968,6 +968,13 @@ final class LazyList[+A] private(private[this] var lazyState: () => LazyList.Sta
*/
@SerialVersionUID(3L)
object LazyList extends SeqFactory[LazyList] {
// Override SeqFactory methods.
override def range[A: Integral](start: A, end: A): LazyList[A] =
range(start, end, step = Integral[A].one)

override def range[A](start: A, end: A, step: A)(implicit ev: Integral[A]): LazyList[A] =
LazyList.iterate(start)(ev.plus(_, step)).takeWhile(ev.lt(_, end))
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// Eagerly evaluate cached empty instance
private[this] val _empty = newLL(State.Empty).force

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14 changes: 13 additions & 1 deletion test/junit/scala/collection/immutable/LazyListTest.scala
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Expand Up @@ -444,8 +444,20 @@ class LazyListTest {
LazyList(1).lazyAppendedAll({ count += 1; Seq(2)}).toList
assertEquals(1, count)
}

@Test
def lazyRangeAllowsMoreThanIntMaxValue(): Unit = {
val totalElements: Long = Int.MaxValue.toLong + 2L
val count: Long =
LazyList
.range(start = 0L, end = totalElements)
.foldLeft(0L) { case (acc, _) =>
acc + 1L
}
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@som-snytt som-snytt Apr 30, 2024

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even with inlining turned on, it's a lot to ask of a unit test. Maybe it's sufficient to test construction and head.

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@BalmungSan BalmungSan Apr 30, 2024

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Yeah I was wondering the same.
However, not sure if just asking for the head ensures there are more than Int.MaxValue elements.

So not sure if there is a smart way to test this without it being a CPU trap.

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@BalmungSan BalmungSan Apr 30, 2024

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Using a reverse range we don't need to compute a lot of elements.
Let me know what you think of the new test.
C.C. @NthPortal

assertEquals(totalElements, count)
}
}

object LazyListTest {
var serializationForceCount = 0
}
}