在 Akka Streams 中使用 Keep.right / Keep.left 不会影响结果

Question

我想举出不同的例子来理解 Keep.left 或 Keep.right

的工作

我有以下代码：

val numSource = Source(1 to 10)
  val numSource = Source(1 to 10)
  val incrementFlow = Flow[Int].map(x => x +1)
  val doubleFlow = Flow[Int].map(x => x * 10)

  val someFuture: NotUsed =           numSource.via(incrementFlow).via(doubleFlow).to(Sink.foreach(println)).run
  val someOtherFuture: Future[Done] = numSource.viaMat(incrementFlow)(Keep.left).viaMat(doubleFlow)(Keep.right).toMat(Sink.foreach(println))(Keep.right).run()
  val someOtherFuture2: Future[Done] = numSource.viaMat(incrementFlow)(Keep.right).viaMat(doubleFlow)(Keep.right).toMat(Sink.foreach(println))(Keep.right).run()

我假设 someOtherFuture viaMat(incrementFlow)(Keep.left) 将忽略元素的增量，因为我使用的是源的物化值（而不是结果 = Keep.right)，图表的结果将等于 num * 10。但是所有 3 行都给我返回相同的结果： //20,30,40 .. 110

我在这里缺少什么？我已经检查了文档并尝试实现简单的示例，但看起来我错了具体化的想法。或者可能是因为我正在使用序列图 w/o 任何接收两个输入的合并流？

Answer 1

最好将物化值理解为流外代码的一种方式（无论是运行还是 completed/failed）以某种方式与流交互：它是 return 运行流的值，我们可以在您发布的代码中看到 Keep.right/Keep.left 的效果：

val someFuture: NotUsed =           numSource.via(incrementFlow).via(doubleFlow).to(Sink.foreach(println)).run
val someOtherFuture: Future[Done] = numSource.viaMat(incrementFlow)(Keep.left).viaMat(doubleFlow)(Keep.right).toMat(Sink.foreach(println))(Keep.right).run()
val someOtherFuture2: Future[Done] = numSource.viaMat(incrementFlow)(Keep.right).viaMat(doubleFlow)(Keep.right).toMat(Sink.foreach(println))(Keep.right).run()

numSource、incrementFlow 和 doubleFlow 的物化值是 NotUsed，这基本上意味着这些阶段不会向流与流交互。

对于 Sink.foreach，物化值是一个 Future[Done]，如果流运行到源耗尽并且所有其他阶段都成功，则它将成功完成 Done，或者完成包含流失败原因的失败。

在 Akka Streams 中使用 Keep.right / Keep.left 不会影响结果

Usage of Keep.right / Keep.left within Akka Streams does not affect the result

scala

akka-stream