相关疑难解决方法(0)

是否有任何真正的理由return在Scala 中提供声明？(除了更"对Java友好")

在下面的代码片段中,我有一个递归函数调用,用于在网络调用失败时促进重试(Amazon SimpleDB偶尔会返回503并需要重试.)

当我尝试编译时,Scala抱怨道recursive method simpledb_update needs result type.

// sends data to SimpleDB. Retries if necessary
def simpledb_update(name: String, metadata: Map[String,String], attempt: Int) = {
 try {
  db(config("simpledb_db")) += (name, metadata)
 } catch {
  case e =>
   // if it fails, try again up to 5 times
  if(attempt < 6)
  {
   Thread.sleep(500)
   simpledb_update(name, metadata, attempt + 1)
   } else
     AUlog(name + ": SimpleDB Failed")
   }
 }

为什么递归函数需要这个？我的想法是只返回一个true/false布尔值来满足编译器...以下编译很好.

// sends data to SimpleDB. Retries if necessary
 def simpledb_update(name: String, …

参考:
Scala 在scala控制器中返回关键字
处理错误

EDIT3
这是"最终"解决方案,再次感谢Dan Burton.

def save = Action { implicit request =>
  val(orderNum, ip) = (generateOrderNum, request.remoteAddress)
  val result = for {
    model   <- bindForm(form).right // error condition already json'd
    transID <- payment.process(model, orderNum) project json
    userID  <- dao.create(model, ip, orderNum, transID) project json
  } yield (userID, transID)
}

然后是pimp'd Either项目方法,放在你的应用程序的某个地方(在我的例子中,一个impbits特性,sbt root和子项目扩展了它们的基础包对象:

class EitherProvidesProjection[L1, R](e: Either[L1, R]) {
  def project[L1, L2](f: L1 => L2) = e match {
    case Left(l:L1) => Left(f(l)).right
    case Right(r)   => Right(r).right …