为了理解 Future[String] 和 Future[List[String]]

Question

简化代码：

val one: Future[String] = Future("1")
val many: Future[List[String]] = Future({"1","2","3"})

for { 
  a <- one
  b <- many
} yield {
  doSomething(a,b) // Type mismatch, expected String, actual: List[String]
}

我想要发生的是调用每对 one/many 并获得输出列表

 {doSomething("1","1"),doSomething("1","2"),doSomething("1","3")}

即使一个是 Future[String] 而另一个是 Future[List[String]]，我能否将其用于理解？

Answer 1

尝试

  val one: Future[String] = Future("1")
  val many: Future[List[String]] = Future(List("1","2","3"))

  def doSomething(a: String, b: String) = ???

  for {
    a <- one
    b <- many
  } yield {
    b.map(v => doSomething(a, v))
  }

或者我们可以像这样使用 scalaz 转换器

  import scalaz._
  import ListT._
  import scalaz.std.scalaFuture.futureInstance

  val one: Future[String] = Future("1")
  val many: Future[List[String]] = Future(List("1","2","3"))

  def doSomething(a: String, b: String) = ???

  for {
    a <- listT(one.map(v => List(v)))
    b <- listT(many)
  } yield {
    doSomething(a, b)
  }

为了理解 Future[String] 和 Future[List[String]]

For comprehension with Future[String] and Future[List[String]]

scala

for-comprehension