Scala Option[Future[T]] 到 Future[Option[T]]

Question

如何转换 Option[Future[T]]至 Future[Option[T]]在斯卡拉？

我想在以下方面使用它:

val customerAddresses = for {
  a <- addressDAO.insert(ca.address) // Future[Address]
  ia <- ca.invoiceAddress.map(addressDAO.insert) // Option[Future[Address]]
} yield (a, ia) // Invalid value have to be two futures

这里签名插入方法

def insert(address: Address): Future[Address]

ca是客户数据

case class CustomerData(address: Address, invoiceAddress: Option[Address])

Answer 1

import scala.concurrent.Future
import scala.concurrent.ExecutionContext

def f[A](x: Option[Future[A]])(implicit ec: ExecutionContext): Future[Option[A]] = 
  x match {
     case Some(f) => f.map(Some(_))
     case None    => Future.successful(None)
  }

例子:

scala> f[Int](Some(Future.successful(42)))
res3: scala.concurrent.Future[Option[Int]] = Success(Some(42))

scala> f[Int](None)
res4: scala.concurrent.Future[Option[Int]] = scala.concurrent.impl.Promise$KeptPromise@c88a337