scala - 如何正确使用 Scala Hashmaps 和 Options？

Question

我的代码片段如下

import scala.collection.mutable.HashMap

val crossingMap = new HashMap[String, Option[Long]]
val crossingData: String = ...
val time: Long = crossingMap.get(crossingData).getOrElse(0)

我收到以下编译错误

error: type mismatch;
found   : Any
required: Long
val time: Long = crossingMap.get(crossingData).getOrElse(0)

Answer 1

您可能想要 crossingMap包含 String -> Long对。然后你可以进行以下操作

val crossingMap = new HashMap[String, Long]
val crossingData: String = ""
val time: Long = crossingMap.getOrElse(crossingData, 0)

如果你真的想要 crossingMap类型为 Option[Long] 的值，那么你必须做一些类似的事情，

val crossingMap = new HashMap[String, Option[Long]]
val crossingData: String = ""
val time: Long = crossingMap.getOrElse(crossingData, None).getOrElse(0)