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str #20262 reduce should fail explicitly on empty stream (#20267)

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* str #20262 reduce should fail explicitly on empty stream

* str #20262 document reduce behaviour on empty stream
This commit is contained in:
Konrad Malawski 2016-04-11 15:36:10 +02:00
parent 503a77f515
commit b9ab232cac
8 changed files with 67 additions and 14 deletions
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5
akka-stream/src/main/scala/akka/stream/javadsl/Sink.scala
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@ -36,6 +36,11 @@ object Sink {
* The returned [[java.util.concurrent.CompletionStage]] will be completed with value of the final
* function evaluation when the input stream ends, or completed with `Failure`
* if there is a failure signaled in the stream.
*
* If the stream is empty (i.e. completes before signalling any elements),
* the reduce stage will fail its downstream with a [[NoSuchElementException]],
* which is semantically in-line with that Scala's standard library collections
* do in such situations.
*/
def reduce[In](f: function.Function2[In, In, In]): Sink[In, CompletionStage[In]] =
new Sink(scaladsl.Sink.reduce[In](f.apply).toCompletionStage())