use SimpleLinearGraphStage to reduce the boilerplate code #21830

akka-stream-tests/src/test/scala/akka/stream/impl/fusing/InterpreterSpec.scala

@@ -577,9 +577,7 @@ class InterpreterSpec extends StreamSpec with GraphInterpreterSpecKit {
 
   }
 
-  private[akka] final case class Doubler[T]() extends GraphStage[FlowShape[T, T]] {
+  private[akka] final case class Doubler[T]() extends SimpleLinearGraphStage[T] {
-    val out: Outlet[T] = Outlet("Doubler.out")
-    val in: Inlet[T] = Inlet("Doubler.in")
 
     override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
       new GraphStageLogic(shape) with InHandler with OutHandler {
@@ -608,12 +606,9 @@ class InterpreterSpec extends StreamSpec with GraphInterpreterSpecKit {
         setHandlers(in, out, this)
       }
 
-    override val shape: FlowShape[T, T] = FlowShape(in, out)
   }
 
-  private[akka] final case class KeepGoing[T]() extends GraphStage[FlowShape[T, T]] {
+  private[akka] final case class KeepGoing[T]() extends SimpleLinearGraphStage[T] {
-    val in = Inlet[T]("KeepGoing.in")
-    val out = Outlet[T]("KeepGoing.out")
 
     override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
       new GraphStageLogic(shape) with InHandler with OutHandler {
@@ -638,7 +633,6 @@ class InterpreterSpec extends StreamSpec with GraphInterpreterSpecKit {
         setHandlers(in, out, this)
       }
 
-    override val shape: FlowShape[T, T] = FlowShape(in, out)
   }
 
   private[akka] class PushFinishStage(onPostStop: () ⇒ Unit = () ⇒ ()) extends SimpleLinearGraphStage[Any] {

akka-stream/src/main/scala/akka/stream/impl/Timers.scala

@@ -176,11 +176,7 @@ object Timers {
 
   }
 
-  final class DelayInitial[T](val delay: FiniteDuration) extends GraphStage[FlowShape[T, T]] {
+  final class DelayInitial[T](val delay: FiniteDuration) extends SimpleLinearGraphStage[T] {
-    val in: Inlet[T] = Inlet("IdleInject.in")
-    val out: Outlet[T] = Outlet("IdleInject.out")
-    override val shape: FlowShape[T, T] = FlowShape(in, out)
-
     override def initialAttributes = DefaultAttributes.delayInitial
 
     override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =

akka-stream/src/main/scala/akka/stream/impl/fusing/GraphStages.scala

@@ -75,11 +75,8 @@ object GraphStages {
   /**
    * INTERNAL API
    */
-  final class Detacher[T] extends GraphStage[FlowShape[T, T]] {
+  final class Detacher[T] extends SimpleLinearGraphStage[T] {
-    val in = Inlet[T]("Detacher.in")
-    val out = Outlet[T]("Detacher.out")
     override def initialAttributes = DefaultAttributes.detacher
-    override val shape = FlowShape(in, out)
 
     override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new GraphStageLogic(shape) with InHandler with OutHandler {
 

akka-stream/src/main/scala/akka/stream/impl/fusing/Ops.scala

@@ -129,11 +129,7 @@ final case class TakeWhile[T](p: T ⇒ Boolean, inclusive: Boolean = false) exte
 /**
  * INTERNAL API
  */
-final case class DropWhile[T](p: T ⇒ Boolean) extends GraphStage[FlowShape[T, T]] {
+final case class DropWhile[T](p: T ⇒ Boolean) extends SimpleLinearGraphStage[T] {
-  val in = Inlet[T]("DropWhile.in")
-  val out = Outlet[T]("DropWhile.out")
-  override val shape = FlowShape(in, out)
-
   override def initialAttributes: Attributes = DefaultAttributes.dropWhile
 
   def createLogic(inheritedAttributes: Attributes) = new SupervisedGraphStageLogic(inheritedAttributes, shape) with InHandler with OutHandler {
@@ -232,12 +228,8 @@ final case class Collect[In, Out](pf: PartialFunction[In, Out]) extends GraphSta
 /**
  * INTERNAL API
  */
-final case class Recover[T](pf: PartialFunction[Throwable, T]) extends GraphStage[FlowShape[T, T]] {
+final case class Recover[T](pf: PartialFunction[Throwable, T]) extends SimpleLinearGraphStage[T] {
-  val in = Inlet[T]("Recover.in")
+  override protected def initialAttributes: Attributes = DefaultAttributes.recover
-  val out = Outlet[T]("Recover.out")
-  override val shape: FlowShape[T, T] = FlowShape(in, out)
-
-  override protected val initialAttributes: Attributes = DefaultAttributes.recover
 
   override def createLogic(inheritedAttributes: Attributes): GraphStageLogic = new GraphStageLogic(shape) with InHandler with OutHandler {
 
@@ -649,16 +641,11 @@ final class FoldAsync[In, Out](zero: Out, f: (Out, In) ⇒ Future[Out]) extends
 /**
  * INTERNAL API
  */
-final case class Intersperse[T](start: Option[T], inject: T, end: Option[T]) extends GraphStage[FlowShape[T, T]] {
+final case class Intersperse[T](start: Option[T], inject: T, end: Option[T]) extends SimpleLinearGraphStage[T] {
   ReactiveStreamsCompliance.requireNonNullElement(inject)
   if (start.isDefined) ReactiveStreamsCompliance.requireNonNullElement(start.get)
   if (end.isDefined) ReactiveStreamsCompliance.requireNonNullElement(end.get)
 
-  private val in = Inlet[T]("in")
-  private val out = Outlet[T]("out")
-
-  override val shape = FlowShape(in, out)
-
   override def createLogic(attr: Attributes): GraphStageLogic = new GraphStageLogic(shape) with OutHandler {
     val startInHandler = new InHandler {
       override def onPush(): Unit = {
@@ -747,11 +734,7 @@ final case class Grouped[T](n: Int) extends GraphStage[FlowShape[T, immutable.Se
 /**
  * INTERNAL API
  */
-final case class LimitWeighted[T](val n: Long, val costFn: T ⇒ Long) extends GraphStage[FlowShape[T, T]] {
+final case class LimitWeighted[T](val n: Long, val costFn: T ⇒ Long) extends SimpleLinearGraphStage[T] {
-  val in = Inlet[T]("LimitWeighted.in")
-  val out = Outlet[T]("LimitWeighted.out")
-  override val shape = FlowShape(in, out)
-
   override def initialAttributes: Attributes = DefaultAttributes.limitWeighted
 
   def createLogic(inheritedAttributes: Attributes) = new SupervisedGraphStageLogic(inheritedAttributes, shape) with InHandler with OutHandler {