我試圖返回一個Map[CharSequence, CharSequence]
。該函數的要點是檢查另一個映射是否具有某個鍵/值對,然後返回特定的CharSequence映射。斯卡拉字符串的地圖不編譯當CharSequence預計
如果我只是返回一個空的地圖(或串地圖),這個編譯
def returnCharSequenceMap(someOtherMap: Option[Map[String,String]]): Map[CharSequence, CharSequence] = {
Map.empty // or something like Map("A" -> "B")
}
然而,這無法編譯
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)
我得到這個,我不能破譯非常無厘頭的錯誤:
[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)
有人可以幫助指出我做錯了什麼嗎?我試圖理解爲什麼我不能只返回地圖。謝謝!