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chore: Matching on seq #2561

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He-Pin wants to merge 1 commit into from
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chore: Matching on seq #2561

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2 changes: 1 addition & 1 deletion stream-tests/src/test/scala/org/apache/pekko/stream/impl/TraversalBuilderSpec.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -521,7 +521,7 @@ class TraversalBuilderSpec extends PekkoSpec {
}

"find Source.iterable via TraversalBuilder with getValuePresentedSource" in {
val iterable = List("a")
val iterable = List("a", "b", "c")
TraversalBuilder.getValuePresentedSource(Source(iterable)).get.asInstanceOf[IterableSource[
String]].elements should ===(
iterable)
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16 changes: 9 additions & 7 deletions stream/src/main/scala/org/apache/pekko/stream/scaladsl/Source.scala
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Expand Up @@ -402,13 +402,15 @@ object Source {
* stream will see an individual flow of elements (always starting from the
* beginning) regardless of when they subscribed.
*/
def apply[T](iterable: immutable.Iterable[T]): Source[T, NotUsed] = {
(iterable.knownSize: @switch) match {
case 0 => empty
case 1 => single(iterable.head)
case _ =>
fromGraph(new IterableSource[T](iterable)).withAttributes(DefaultAttributes.iterableSource)
}
def apply[T](iterable: immutable.Iterable[T]): Source[T, NotUsed] = iterable match {
case immutable.Seq() => empty[T]
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@pjfanning pjfanning Dec 8, 2025

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I don't see how adding extra checks, including instanceof checks, improves performance. Is there any way that we could keep a variant of the old code from the recent other PR that introduced changes?

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@He-Pin He-Pin Dec 8, 2025 •
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It's vs the materialization

case immutable.Seq(elem: T @unchecked) => single(elem)
case other => (other.knownSize: @switch) match {
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@pjfanning pjfanning Dec 8, 2025

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Can you add a comment saying that if the Iterable has unknown size, that knownSize returns -1?

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@He-Pin He-Pin Dec 8, 2025

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It's not unknown size,just the size can or not been cheaply cimputed

case 0 => empty
case 1 => single(iterable.head)
case _ =>
fromGraph(new IterableSource[T](iterable)).withAttributes(DefaultAttributes.iterableSource)
}
}

/**
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