Scala Option的收集方法不像我的PartialFunction
我想我错过了一些东西：
scala> Some(1) collect ({ case n if n > 0 => n + 1; case _ => 0})
res0: Option[Int] = Some(2)
scala> None collect ({ case n if n > 0 => n + 1; case _ => 0})
<console>:6: error: value > is not a member of Nothing
None collect ({ case n if n > 0 => n + 1; case _ => 0})
^
<console>:6: error: value + is not a member of Nothing
None collect ({ case n if n > 0 => n + 1; case _ => 0})
collect
没有找到相关结果
已邀请:
2 个回复
埃庐
的类型为。这是必要的，因为None必须是所有类型Option [_]的有效成员。如果你改写了(None:Option[Int]) collect ({ case n if n > 0 => n + 1; case _ => 0})val x:Option[Int] = None x collect ({ case n if n > 0 => n + 1; case _ => 0})闲窍
None collect ({ case n if n > 0 => n + 1; case _ => 0})有的方法？那里没有任何东西允许编译器假设这一点。所以，尝试将其更改为：None collect ({ case n: Int if n > 0 => n + 1; case _ => 0})<console>:8: error: pattern type is incompatible with expected type; found : Int required: Nothing None collect ({ case n: Int if n > 0 => n + 1; case _ => 0}) ^是不可能的，因为你只是传递。碰巧，的类型为。