scala - 无法在 [[scala.concurrent.Future]] 上获取 `pipeTo` 方法

Question

正如 akka 的文档所解释的，您应该能够通过这种方式获得 [[scala.concurrent.Future]] 上的 pipeTo 方法:

import akka.pattern.pipe
val future = ...
future pipeTo sender()

不幸的是，我不能这样做，我在 IDE 中收到错误“无法解析符号 pipelineTo”。

作为解决方法，我必须以这种方式使用语法

pipe(future) pipeTo sender()

但它仍然让我不明白为什么(顺便说一句，我对 scala 很陌生)。非常感谢您帮助理解这个难题。

scala 2.12.2 Akka 2.5.3

Answer 1

您需要在范围内有一个隐式 ExecutionContext，下面是一个示例:

import akka.actor.{Actor, ActorSystem, Props}
import akka.pattern.pipe

import scala.concurrent.Future

// Get the implicit ExecutionContext from this import
import scala.concurrent.ExecutionContext.Implicits.global

object Hello extends App {

  // Creating a simple actor
  class MyActor extends Actor {
    override def receive: Receive = {
      case x => println(s"Received message: ${x.toString}")
    }
  }

  // Create actor system
  val system = ActorSystem("example")
  val ref = system.actorOf(Props[MyActor], "actor")

  // Create the future to pipe
  val future: Future[Int] = Future(100)

  // Test
  future pipeTo ref
}

控制台:

sbt run
[info] <stuff here>
[info] Running example.Hello 
Received message: 100

<小时/>

您必须这样做的原因是因为 pipeTo 是 PipeableFuture 上的实例函数，并且您的常规 Future 必须是“增强”为 PipeableFuture。这是PipeableFuture的构造函数，注意隐式executionContext:ExecutionContext参数:

final class PipeableFuture[T](val future: Future[T])(implicit executionContext: ExecutionContext)

完整的类在这里，您可以在其中看到 pipeTo 函数:

final class PipeableFuture[T](val future: Future[T])(implicit executionContext: ExecutionContext) {
  def pipeTo(recipient: ActorRef)(implicit sender: ActorRef = Actor.noSender): Future[T] = {
    future andThen {
      case Success(r) ⇒ recipient ! r
      case Failure(f) ⇒ recipient ! Status.Failure(f)
    }
  }
  def pipeToSelection(recipient: ActorSelection)(implicit sender: ActorRef = Actor.noSender): Future[T] = {
    future andThen {
      case Success(r) ⇒ recipient ! r
      case Failure(f) ⇒ recipient ! Status.Failure(f)
    }
  }
  def to(recipient: ActorRef): PipeableFuture[T] = to(recipient, Actor.noSender)
  def to(recipient: ActorRef, sender: ActorRef): PipeableFuture[T] = {
    pipeTo(recipient)(sender)
    this
  }
  def to(recipient: ActorSelection): PipeableFuture[T] = to(recipient, Actor.noSender)
  def to(recipient: ActorSelection, sender: ActorRef): PipeableFuture[T] = {
    pipeToSelection(recipient)(sender)
    this
  }
}

由于 pipe(future) 不是 Future 上的实例函数，因此它可以在您的示例中工作。