scala - 获取任何一个的值(value)

Question

除了使用 match , 是否有类似 Option 的方式到 getOrElse Right的实际内容或 Left值(value)？

scala> val x: Either[String,Int] = Right(5)
scala> val a: String = x match { 
                                case Right(x) => x.toString
                                case Left(x) => "left" 
                       }
a: String = 5

Answer 1

我不是特别喜欢Either因此，我对它并不十分熟悉，但我相信您正在寻找预测:either.left.getOrElse或 either.right.getOrElse .

请注意，预测也可用于理解。这是直接来自文档的示例:

def interactWithDB(x: Query): Either[Exception, Result] =
  try {
    Right(getResultFromDatabase(x))
  } catch {
    case ex => Left(ex)
  }

// this will only be executed if interactWithDB returns a Right
val report =
  for (r <- interactWithDB(someQuery).right) yield generateReport(r)
if (report.isRight)
  send(report)
else
  log("report not generated, reason was " + report.left.get)