Swift 中的 append 函数是如何工作的? [英] How does append function work in Swift?

问题描述

谁能解释一下这个说法有什么问题.

Can someone explain me what is wrong with this statement.

var someString = "Welcome"
someString.append("!")

但是，当我用以下代码替换代码时，这是可行的，

However this works when I replace the code with,

var someString = "Welcome"
let exclamationMark : Character = "!"
someString.append(exclamationMark)

提前致谢

推荐答案

在 Swift 中，没有字符字面量(例如 C 派生语言中的 'c')，只有 String 文字.

In Swift, there is no character literal (such as 'c' in C-derived languages), there are only String literals.

然后，您在 Strings 上定义了两个函数:append，用于附加单个字符，以及 extend，用于附加整个细绳.所以这是有效的:

Then, you have two functions defined on Strings: append, to append a single character, and extend, to append a whole String. So this works:

var someString = "Welcome"
someString.extend("!")

如果你真的想使用append，你可以通过调用强制将一个字符的String文字转换为CharacterCharacter 的构造函数:

If you really want to use append, you can force a one-char String literal to be turned into a Character either by calling Character's constructor:

someString.append(Character("!"))

或使用类型转换:

someString.append("!" as Character)

或者像使用额外变量一样使用类型注释:

or by using a type annotation as you did with an extra variable:

let exclamationMark: Character = "!"
someString.append(exclamationMark)

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