Swift官方文档同步的中文快速入门教程

建议: 重点理解一下字符串的底层表示, 相应部分从 Unicode 开始看起

字符串字面量 (String Literals)

let s = "hello"

多行字符串字面量 (Multiline String Literals)

🕐 多行字符串表示法, :

let s = """
hear me now and bear witness to my vow
night gathers and now my watch begins
"""

🕑 使用 \ 在代码层面换行, 实际文字不换行:

let s = """
hear me now and bear witness\
to my vow
night gathers and now my watch begins
"""

🕒 首行缩进以末尾 """ 所在行的缩进为基准:

![[Pasted image 20240107172813.png]]

特殊字符 (Special Characters in String Literals)

转义字符有:

let a = "\u{24}"        // $,  Unicode scalar U+0024
let b = "\u{2665}"      // ♥,  Unicode scalar U+2665
let c = "\u{1F496}" // 💖, Unicode scalar U+1F496

扩展的字符串界定符 (Extended String Delimiters)

通过在字符串外层使用 # (任意个数)达到在原生字符串的效果

🕐 以下是等价的:

let s1 = #"Here are : \n"#
let s2 = ##"Here are : \n"##
let s3 = ###"Here are : \n"###

🕑 在 \ 后添加界定符以恢复特殊字符的效果:

let s1 = #"Here are : \#n"#
let s2 = ##"Here are : \##n"##
let s3 = ###"Here are : \##n"###

初始化空字符串 (Initializing an Empty String)

🕐 初始化空字符串:

var s1 = ""
var s2 = String()

🕑 判断是否为空:

if s.isEmpty {
	...
}

字符串的可变性 (String Mutability)

是否可变取决于是 var 还是 let

字符串是值类型 (Strings Are Value Types)

值类型意味着是值存储和传递, 而不是指针

使用字符 (Working with Characters)

🕐 字符串是字符数组:

for c in "Dog!🐶" {
    print(c)
}

🕑 定义字符:

let c: Character = "!"

🕒 将字符数组转换为字符串:

let c: [Character] = ["C", "a", "t", "!", "🐱"]
let s = String(c)

拼接字符和字符串 (Concatenating Strings and Characters)

🕐 拼接:

let a = "hello"
let b = " world"
let s = a + b

🕑 复合拼接:

var s = "hello"
s += " world"

🕒 末尾添加字符:

var s = "hello"
s.append("!")

字符串插值 (String Interpolation)

🕐 使用 \() 在字符串中进行插值:

var a = "root"
let b = "hello \(a)"

🕑 在扩展的字符串界定符中进行插值:

print(#"6 times 7 is \#(6 * 7)."#)

Unicode

String 完全符合 Unicode 标准, 组成字符串的基本单位不再是"字符"

Unicode 标量值 (Unicode Scalar Values)

String 由 Unicode 标量值组成

扩展字素簇 (Extended Grapheme Clusters)

Character 表示一个单独的"扩展字素簇", 即可由多个 Unicode 标量值组成的序列

🕐 如二者都表示 é:

let a: Character = "\u{E9}"
let b: Character = "\u{65}\u{301}" 
print(a == b) // true

🕑 扩展字素簇可通过组合或拆解的形式表示:

let a: Character = "\u{D55C}" // 한 
let b: Character = "\u{1112}\u{1161}\u{11AB}" // ᄒ, ᅡ, ᆫ
print(a == b) // true

🕒 可以给 Unicode 标量进行字符修饰; 如给它添加某个符号:

let a: Character = "\u{E9}\u{20DD}"

但是其仍然被视为 Character

🕔 组合地区指示符:

let a: Character = "\u{1F1FA}\u{1F1F8}"
print(a) // 🇺🇸

计算字符数量 (Counting Characters)

var s = "root"
print(s.count) // 4

计算字符数量需要遍历最底层 Unicode 标量值, 因而字符串越长性能也越差

访问和修改字符串 (Accessing and Modifying a String)

字符串索引 (String Indices)

每个字符串值都有其对应的索引类型 String.Index 来标识每个字符所在的位置, 由于字符串的特殊组成, 需要遍历 Unicode 标量值来决定每个字符的位置, 因而不能直接使用数值索引

let s = "abcdefg"

🕐 获取首字符:

s[s.startIndex] // a

🕑 获取指定字符前或后的字符:

s[s.index(before: s.endIndex)] // g
s[s.index(after: s.startIndex)] // b

其中 endIndex 指向最后一个字符的下一位置

🕒 获取指定偏移位置的索引:

let index = s.index(s.startIndex, offsetBy: 3)
print(s[index]) // d

🕓 通过索引遍历字符串:

for i in s.indices {
    print(s[i])
}

这种索引类型适用于任何遵循 Collection 协议的类型, 比如 Array, Dictionary 和 Set

插入和移除 (Inserting and Removing)

var s = "abcdefg"

🕐 在指定索引处插入字符:

s.insert("h", at: s.endIndex)

🕑 移除指定索引处的字符:

s.remove(at: s.index(before: s.endIndex))

🕒 移除指定索引范围内的字符:

let range = s.index(s.endIndex, offsetBy: -2) ..< s.endIndex
s.removeSubrange(range)

上述方法适用于任何遵循 Collection 协议的类型, 比如 Array, Dictionary 和 Set

子串 (Substrings)

子串是一个类型 Substring, 相当于是字符串的视图, 当你对子串进行修改时, 其会被转换为字符串
![[Pasted image 20240221154649.png|350]]

🕐 通过索引获取子串:

var s = "abc,def,g"
let index = s.firstIndex(of: ",") ?? s.endIndex
let a = s[..<index]

🕑 将字串转换为字符串:

let b = String(a)

字符串比较 (Comparing Strings)

🕐 比较字符串的值是否相等:

let a = "I'm root"
let b = "I'm root"
if a == b {
    print("equal")
}

🕑 需要注意扩展字素簇的情况:

let a = "Voulez-vous un caf\u{E9}?"
let b = "Voulez-vous un caf\u{65}\u{301}?"
if a == b {
    print("equal")
}

因为 \\u{65}\\u{301} 为 \\u{E9} 的扩展表示

前缀与后缀 (Prefix and Suffix Equality)

let list = [
    "Act 1 Scene 1: Verona, A public place",
    "Act 1 Scene 2: Capulet's mansion",
    "Act 1 Scene 3: A room in Capulet's mansion",
    "Act 1 Scene 4: A street outside Capulet's mansion",
    "Act 1 Scene 5: The Great Hall in Capulet's mansion",
    "Act 2 Scene 1: Outside Capulet's mansion",
    "Act 2 Scene 2: Capulet's orchard",
    "Act 2 Scene 3: Outside Friar Lawrence's cell",
    "Act 2 Scene 4: A street in Verona",
    "Act 2 Scene 5: Capulet's mansion",
    "Act 2 Scene 6: Friar Lawrence's cell"
]

判断 String 是否拥有指定的前缀或后缀:

for i in list {
    if i.hasPrefix("Act 1") { // 是否拥有前缀
        print("prefix")
    }
    
    if i.hasSuffix("cell") { // 是否拥有后缀
        print("suffix")
    }
}

字符串的 Unicode 表示形式 (Unicode Representations of Strings)

获取 String 的不同表示方式

let dogString = "Dog‼🐶"

UTF-8 形式 (UTF-8 Representation)

![[Pasted image 20240226165335.png]]

for codeUnit in dogString.utf8 {
    print("\(codeUnit) ", terminator: "")
}
// 68 111 103 226 128 188 240 159 144 182

UTF-16 形式 (UTF-16 Representation)

![[Pasted image 20240226165345.png|550]]

for codeUnit in dogString.utf16 {
    print("\(codeUnit) ", terminator: "")
}
// 68 111 103 8252 55357 56374

Unicode 标量值形式 (Unicode Scalar Representation)

![[Pasted image 20240226165504.png|500]]

for scalar in dogString.unicodeScalars {
    print("\(scalar.value) ", terminator: "")
}
// 68 111 103 8252 128054

🕐 可以直接将该标量值转换为 String:

for scalar in dogString.unicodeScalars {
    print("\(scalar) ")
}
// D
// o
// g
// ‼
// 🐶
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