单个 arg 匿名函数的简明符号(避免下划线)未按预期工作 [英] Concise notation for single arg anonymous function (avoiding underscore) not working as expected

问题描述

在浏览了网络上的一些示例后，我意识到有一种方法可以在只有单个 arg 时编写不带下划线的匿名函数.另外，我正在尝试使用 List 上的span"方法，我从来不知道它存在.无论如何，这是我的 REPL 会话:

After going through some examples on the web I realize that there is a way to write an anonymous function without the underscore when only a single arg. Also, I'm experimenting with the "span" method on List, which I never knew existed. Anyway, here is my REPL session:

scala> val nums = List(1, 2, 3, 4, 5)
nums: List[Int] = List(1, 2, 3, 4, 5)

scala> nums span (_ != 3)
res0: (List[Int], List[Int]) = (List(1, 2),List(3, 4, 5))

scala> nums span (3 !=)
res1: (List[Int], List[Int]) = (List(1, 2),List(3, 4, 5))

到目前为止一切顺利.但是当我尝试使用小于"运算符时:

So far so good. But when I try to use the "less than" operator:

scala> nums span (_ < 3)
res2: (List[Int], List[Int]) = (List(1, 2),List(3, 4, 5))

scala> nums span (3 <)
res3: (List[Int], List[Int]) = (List(),List(1, 2, 3, 4, 5))

为什么这表现不同?

推荐答案

scala> nums span (_ < 3)
res0: (List[Int], List[Int]) = (List(1, 2),List(3, 4, 5))

scala> nums span (3 >)
res1: (List[Int], List[Int]) = (List(1, 2),List(3, 4, 5))

3 是 3 的快捷方式_，它通过方法调用创建一个部分应用的函数.

3 < is a shortcut to 3 < _, which creates a partially applied function from method call.

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