Scala语法奇怪与::并要求小写

发布时间：2020-12-16 18:54:45 所属栏目：安全来源：网络整理

导读：这应该发生吗？ scala val myList = List(42)myList: List[Int] = List(42)scala val s2 :: Nil = myLists2: Int = 42scala val S2 :: Nil = myListconsole:8: error: not found: value S2 val S2 :: Nil = myList ^ 它似乎区分大小写.错误或“功能”？解决

这应该发生吗？

scala> val myList = List(42)
myList: List[Int] = List(42)

scala> val s2 :: Nil = myList
s2: Int = 42

scala> val S2 :: Nil = myList
<console>:8: error: not found: value S2
       val S2 :: Nil = myList
           ^

它似乎区分大小写.错误或“功能”？

解决方法

它区分大小写.在匹配模式中,以大写字母开头(或由反引号引用)的标识符被视为对定义值的引用,而不是新绑定.

这让很多人感到意外,而且阅读Scala语言规范并不是很明显.最相关的位是“variable patterns”……

A variable pattern x is a simple identifier which starts with a lower case letter. It matches any value,and binds the variable name to that value.

……和“stable identifier patterns”：

To resolve the syntactic overlap with a variable pattern,a stable identifier pattern may not be a simple name starting with a lower-case letter.