价值 |@|不是 scala.concurrent.Future[String] 的成员

Question

我正在尝试使用 Scalaz 的应用构建器来简化一些并行运行多个期货的代码：

import scalaz._, Scalaz._

val fooF: Future [String] = myService.getFoo ()
val barF: Future [String] = myService.getBar ()
val resultF = for {
  foo <- fooF
  bar <- barF
}
yield { foo + bar }

我知道我应该能够像这样重写上面的代码：

val resultF = (myService.getFoo () |@| myService.getBar ()) {
  (foo, bar) => { foo + bar }
}

但是我收到以下编译错误：

value |@| is not a member of scala.concurrent.Future[String]

我做错了什么？

Answer 1

您需要在范围内具有隐式 ExecutionContext，它需要为 Future（以及 Monad 等）构建 Applicative

  import scalaz._, Scalaz._

  import scala.concurrent.{Await, Future}
  import scala.concurrent.duration._

  import scala.concurrent.ExecutionContext.Implicits.global

  val fooF: Future [String] = Future("aaa")
  val barF: Future [String] = Future("bbb")

  val result = (fooF |@| barF)((l, r) => s"$l$r")

  println(Await.result(result, 10.seconds))

更新

你可以在 scalaz.std.Future.scala 中查看

implicit def futureInstance(implicit ec: ExecutionContext): Monad[Future] with Cobind[Future] =
    new FutureInstance