Scala Akka Streams 项目编译失败，“value ~> is not a member of akka.streams.Outlet[In]”

Question

我在一个 Scala 项目中使用 Akka Streams API，在 Intellij IDEA 中使用 SBT 插件工作。我有一个工作池流，如下所述：https://doc.akka.io/docs/akka/current/scala/stream/stream-cookbook.html。这是我的代码：

package streams

import akka.NotUsed
import akka.stream.scaladsl.{Balance, Flow, GraphDSL, Merge}
import akka.stream.{FlowShape, Graph}

object WorkerPoolFlow {
  def apply[In, Out](
    worker: Flow[In, Out, Any],
    workerCount: Int):
  Graph[FlowShape[In, Out], NotUsed] = {

    GraphDSL.create() { implicit b =>

      val balance = b.add(Balance[In](workerCount, waitForAllDownstreams = true))
      val merge   = b.add(Merge[Out](workerCount))

      for (i <- 0 until workerCount)
        balance.out(i) ~> worker.async ~> merge.in(i)

      FlowShape(
        balance.in,
        merge.out)
    }
  }
}

由于某种原因，项目现在无法编译，出现以下错误：value ~> is not a member of akka.stream.Outlet[In]。

直到今天它编译得很好。我知道的唯一改变是安装一个 Scala linter 插件scalafmt，并在build.sbt 中导入一些新库。这是我的build.sbt：

name := "myProject"

version := "0.1"

scalaVersion := "2.11.11"

unmanagedJars in Compile += file("localDep1.jar")
unmanagedJars in Compile += file("localDep2.jar")

libraryDependencies += "io.spray" %%  "spray-json" % "1.3.3"
libraryDependencies += "com.typesafe.akka" %% "akka-actor" % "2.5.6"
libraryDependencies += "com.typesafe.akka" %% "akka-stream" % "2.5.6"
libraryDependencies += "com.typesafe.akka" %% "akka-testkit" % "2.5.6" % Test
libraryDependencies += "com.typesafe.akka" %% "akka-stream-testkit" % "2.5.6" % Test
libraryDependencies += "com.47deg" %% "fetch" % "0.6.0"
libraryDependencies += "ch.qos.logback" % "logback-classic" % "1.2.3"

我尝试过重新加载 SBT、在 IDEA 之外从 SBT 构建、删除和重新添加依赖项以及清理项目，但没有成功。

Answer 1

导入GraphDSL.Implicits._:

object WorkerPoolFlow {
  def apply[In, Out](
    worker: Flow[In, Out, Any],
    workerCount: Int):
  Graph[FlowShape[In, Out], NotUsed] = {
    import GraphDSL.Implicits._

    GraphDSL.create() { implicit b =>
      ...
    }
  }
}