我试图返回一个Map[CharSequence, CharSequence]
。该函数的要点是检查另一个映射是否具有某个键/值对,然后返回特定的CharSequence映射。斯卡拉字符串的地图不编译当CharSequence预计
如果我只是返回一个空的地图(或串地图),这个编译
def returnCharSequenceMap(someOtherMap: Option[Map[String,String]]): Map[CharSequence, CharSequence] = {
Map.empty // or something like Map("A" -> "B")
}
然而,这无法编译
def returnCharSequenceMap(someOtherMap: Option[Map[String, String]]): Map[CharSequence, CharSequence] = {
someOtherMap.map { mapRecord =>
case Some("conditionA") =>
Map("a" -> "b")
case Some("conditionB") =>
Map("a" -> "b", "c" -> "d")
case _ => Map.empty
}
}.getOrElse(Map.empty)
我得到这个,我不能破译非常无厘头的错误:
[error] found : scala.collection.immutable.Map[_19,String] where type _19 >: _1 <: CharSequence
[error] required: Map[CharSequence,CharSequence]
[error] Note: _19 <: CharSequence, but trait Map is invariant in type A.
[error] You may wish to investigate a wildcard type such as `_ <: CharSequence`. (SLS 3.2.10)
[error] }.getOrElse(Map.empty)
有人可以帮助指出我做错了什么吗?我试图理解为什么我不能只返回地图。谢谢!