Scala 点语法(或缺少语法)

问题描述

我正在阅读精彩的书在 Scala 中编程遇到一段对我来说毫无意义的代码:

I was going through the wonderful book Programming in Scala when I came across a piece of code that just doesn't make sense to me:

def above(that: Element): Element = {
    val this1 = this widen that.width
    val that1 = that widen this.width
    elem(this1.contents ++ that1.contents)
}

注意第 2 行和第 3 行:

Note line 2 and 3:

val this1 = this widen that.width

看来我应该可以用:

val this1 = this.widen that.width

但是，当我尝试编译此更改时，会出现以下错误:

However, when I try to compile this change, it gives the following error:

错误:';'预期但'.'成立.
val this1 = this.widen that.width^

为什么这种语法不可接受?

Why is this syntax unacceptable?

推荐答案

第 2 行将方法 widen 用作操作符，而不是将其用作 Java 方式中的方法:

Line 2 uses the method widen as an operator, instead of using it as a method in the Java way:

val this1 = this.widen(that.width)

发生错误是因为您省略了括号，只有在使用运算符表示法的方法时才能这样做.您不能这样做，例如:

The error occurs because you've left out the parentheses, which you can only do when you use a method in operator notation. You can't do this for example:

"a".+ "b" // error: ';' expected but string literal found.

你应该写

"a".+ ("b")

实际上你可以用整数来做到这一点，但这超出了这个问题的范围.

Actually you can do this with integers, but that's beyond the scope of this question.

阅读更多:

• 您的书的第 5 章第 3 节是关于运算符表示法的，至少在第一版第 5 版中是这样的
• Scala 之旅:运算符

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