scala – 如何键入匿名PartialFunction
发布时间:2020-12-16 10:04:39 所属栏目:安全 来源:网络整理
导读:这有效: scala List(1,"aa") collect { case n : Int = n+2 } res52: List[Int] = List(3) 这很好用: scala var f:PartialFunction[Any,Int] = { case n : Int = n+2 }f: PartialFunction[Any,Int] = function1scala var g:PartialFunction[Any,String] =
这有效:
scala> List(1,"aa") collect { case n : Int => n+2 } res52: List[Int] = List(3) 这很好用: scala> var f:PartialFunction[Any,Int] = { case n : Int => n+2 } f: PartialFunction[Any,Int] = <function1> scala> var g:PartialFunction[Any,String] = { case n : String => n + " plus two " } g: PartialFunction[Any,String] = <function1> scala> List(1,"aa") collect (f orElse g) res51: List[Any] = List(3,"aa plus two ") 但如果我试着将两者结合在一起,那么: scala> List(1,"aa") collect { case n : Int => n+2 } orElse { case n : String => n + " plus two " } <console>:8: error: missing parameter type for expanded function The argument types of an anonymous function must be fully known. (SLS 8.5) Expected type was: PartialFunction[?,?] List(1,"aa") collect { case n : Int => n+2 } orElse { case n : String => n + " plus two " } 我不明白为什么推理会失败,但我可以猜到.重要的问题:我该如何解决? 解决方法
您需要告诉编译器您的匿名PartialFunctions的参数类型.您可以通过注释其类型直接执行此操作:
List(1,"aa") collect ({ { case n : Int => n+2 }: PartialFunction[Any,_] } orElse { { case n : String => n + " plus two " }: PartialFunction[Any,_] }) 请注意,必须将表达式括在括号中的collect右侧. 如果你不喜欢罗嗦,并且你不介意试图理解你的代码的人感到沮丧,你可以在PartialFunctions上定义一个输入类型为Any的身份函数: def pfa[T](f: PartialFunction[Any,T]): PartialFunction[Any,T] = f List(1,"aa") collect ( pfa { case n : Int => n+2 } orElse pfa { case n : String => n + " plus two " } ) 您甚至可以提出一个非常奇怪的名称并假装它是Scala语言功能: def @:[T](f: PartialFunction[Any,T] = f scala> @:{case x: Int => x + 3} res29: PartialFunction[Any,Int] = <function1> (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |