为什么 Swift 的三元运算符对空格如此挑剔? [英] Why is Swift's ternary operator so picky about whitespace?

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问题描述

问题很简单,但我就是找不到答案!

The question is very simple, but I just could not find the answer!

为什么不

return x == 0? "" : "Hello"

编译不过

return x == 0 ? "" : "Hello"

有吗?

这真的很奇怪,因为所有其他运算符都不需要额外的空格.例如

This is really weird because all the other operators don't need an extra white space. e.g.

let x = 1+1
let y = 1 + 1

都一样.

我认为这与选项有关.但是当你在一个变量上使用 ? 操作符时,它必须像这样使用:

I think it has something to do with optionals. But when you use a ? operator on a variable, it must be used like this:

let s: String? = nil
let x = s?.startIndex

我的意思是它必须跟随另一个操作员,对吗?

I mean it must follow another operator, right?

推荐答案

我认为这与选项有关.

I think it has something to do with optionals.

确实如此.运营商 说:

[关于运算符周围的空格] 规则有一个警告.如果 !? 预定义运算符左侧没有空格,则将其视为后缀运算符,无论其右侧是否有空格.要将 ? 用作可选链运算符,它的左侧不能有空格.要在三元条件 (? :) 运算符中使用它,它的两边必须有空格.

There is one caveat to the rules [regarding whitespace around operators]. If the ! or ? predefined operator has no whitespace on the left, it is treated as a postfix operator, regardless of whether it has whitespace on the right. To use the ? as the optional-chaining operator, it must not have whitespace on the left. To use it in the ternary conditional (? :) operator, it must have whitespace around both sides.

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