Question

鉴于案例类Person定义为：

case class Person ( first: String, middle: String, last: String )

案例类Band包含许多Person s：

case class Band ( name: String, members: List[Person] )

我需要的是为乐队中的每个成员添加Person的中间首字母，同时考虑函数getMiddle实际上是Future。这是我的尝试：

case class Person ( first: String, middle: String, last: String )
case class Band ( name: String, members: List[Person] )

object TestFutures3 extends App {

  val p1 = Person ( "David", "", "Gahan" )
  val p2 = Person ( "Martin", "", "Gore" )
  val band = Band ( "Depeche Mode", List(p1,p2) )

  def getMiddle (name: String) = Future { 
    if (name == "Martin")
      "L"
    else
      "X"
  }

  val membersWithMiddle = band.members.map { 
              p => Person(p.first, getMiddle(p.first).map(_), p.last)
         }  

  println(membersWithMiddle)

  Thread.sleep(5000)
}

Answer 1

您可以使用Future.traverse：

import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

val setMiddleName: Person => Future[Person] =
  member => getMiddle(member.first).map(middle => member.copy(middle = middle))

val bandMembers: Future[List[Person]] =
  Future.traverse(band.members)(setMiddleName)

bandMembers.foreach(println)
// List(Person(David,X,Gahan), Person(Martin,L,Gore))

Future.traverse在这种情况下采用List[Person]和Person => Future[Person]函数（将针对每个Person执行 - 除非其中一个Future s失败）并返回Future[List[Person]]。

Answer 2

你可以等待未来，直接分配中间：

val middle = Await.result(getMiddle(p.first), Duration.Inf)
val x: Person = Person(p.first, middle, p.last)

或者你可以回来一个未来的人：

val x: Future[Person] = getMiddle(p.first).map(middle => Person(p.first, middle, p.last)

在循环中调用Future方法

2 个答案: