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Support java collections & streams in for-do loops #15379

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Support java collections & streams in for-do loops #15379

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8 changes: 8 additions & 0 deletions library/src/scala/runtime/stdLibPatches/Predef.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -60,4 +60,12 @@ object Predef:
inline def ne(inline y: AnyRef | Null): Boolean =
!(x eq y)

extension [T](it: java.lang.Iterable[T])
def foreach(f: java.util.function.Consumer[T]): Unit =
it.forEach(f)

extension [T](s: java.util.stream.Stream[T])
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Should we also support IntStream and the other primitive streams?

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@TheElectronWill TheElectronWill Jun 10, 2022 •
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It we could support BaseStream (javadoc), which is the common interface above Stream, IntStream and all, it would be even better :)
edit: actually I got carried away: BaseStream doesn't provide any meaningful operation on its elements...

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I think it would be good to also support IntStream and the other primitive streams.

def foreach(f: java.util.function.Consumer[T]): Unit =
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@odersky odersky Jun 15, 2022 •
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If it is in Predef then foreach needs to be inline, since stdLibPatches/Predef.scala has no runtime equivalent. Or else we need a PR against 2.13 Predef instead.

s.forEach(f)

end Predef
13 changes: 13 additions & 0 deletions tests/pos/java-collection-for-do.scala
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@@ -0,0 +1,13 @@
import java.util.{List, ArrayList}
import java.util.stream.Stream

object JavaCollectionForDo {

for
x <- scala.List(1, 2, 3)
y <- List.of(1, 2, 3)
z <- Stream.of(1, 2, 3)
do
println(x + y + z)

}