为什么三元运算符如此之快? [英] Why ternary operator in swift is so picky?

问题描述

这个问题很简单，但我只是找不到答案！

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

为什么不

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

编译但

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

是吗?

这真的很奇怪，因为所有其他运算符都不需要多余的空格.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

一样.

我认为这与可选内容有关.但是，当在变量上使用?运算符时，必须像这样使用它:

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运算符，对吗?

I mean it must follow another operator, right?

推荐答案

我认为这与可选内容有关.

I think it has something to do with optionals.

是的.

规则[关于运算符周围的空白]有一个警告.如果!或?预定义运算符在左侧没有空格，则无论其右侧是否有空格，都将其视为后缀运算符.要将?用作可选链接运算符，它的左侧不得有空格.要在三元条件运算符(? :)中使用它，它的左右两侧都必须有空格.

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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