Swift3.0中文教程：3.字符串和字符

字符串和字符（Strings and Characters）

String

Character

String

String

Character

+

String

String

NSString

AnyObject

NSString

NSString

NSString

String

String

字符串字面量（String Literals）

""

let someString = "Some string literal value"

someString

String

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

String

var emptyString = ""               // 空字符串字面量
var anotherEmptyString = String()  // 初始化方法
// 两个字符串均为空并等价。

Bool

isEmpty

if emptyString.isEmpty {
print("Nothing to see here")
}
// 打印输出："Nothing to see here"

字符串可变性 (String Mutability)

var variableString = "Horse"
variableString += " and carriage"
// variableString 现在为 "Horse and carriage"

let constantString = "Highlander"
constantString += " and another Highlander"
// 这会报告一个编译错误 (compile-time error) - 常量字符串不可以被修改。

NSString

NSMutableString

字符串是值类型（Strings Are Value Types）

String

使用字符（Working with Characters）

for-in

characters

for character in "Dog!".characters {
print(character)
}
// D
// o
// g
// !

for-in

Character

let exclamationMark: Character = "!"

Character

let catCharacters: [Character] = ["C", "a", "t", "!"]
let catString = String(catCharacters)
print(catString)
// 打印输出："Cat!"

连接字符串和字符 (Concatenating Strings and Characters)

+

let string1 = "hello"
let string2 = " there"
var welcome = string1 + string2
// welcome 现在等于 "hello there"

+=

var instruction = "look over"
instruction += string2
// instruction 现在等于 "look over there"

append()

let exclamationMark: Character = "!"welcome.append(exclamationMark)
// welcome 现在等于 "hello there!"

字符串插值 (String Interpolation)

let multiplier = 3
let message = "\(multiplier) times 2.5 is \(Double(multiplier) * 2.5)"
// message is "3 times 2.5 is 7.5"

multiplier

\(multiplier)

multiplier

multiplier

Double(multiplier) * 2.5

7.5

\(Double(multiplier) * 2.5)

\

Unicode

String

Character

Unicode 标量（Unicode Scalars）

String

U+0061

LATIN SMALL LETTER A

a

U+1F425

FRONT-FACING
BABY CHICK

U+0000

U+D7FF

U+E000

U+10FFFF

U+D800

U+DFFF

LATIN SMALL LETTER A

FRONT-FACING BABY CHICK

字符串字面量的特殊字符 (Special Characters in String Literals)

\0

\\

\t

\n

\r

\"

\'

\u{n}

n

wiseWords

dollarSign

blackHeart

sparklingHeart

let wiseWords = "\"Imagination is more important than knowledge\" - Einstein"
// "Imageination is more important than knowledge" - Enistein
let dollarSign = "\u{24}"             // $, Unicode 标量 U+0024
let blackHeart = "\u{2665}"           // ♥, Unicode 标量 U+2665

可扩展的字形群集(Extended Grapheme Clusters)

Character

é

é

LATIN SMALL LETTER E WITH ACUTE

U+00E9

e

LATIN
SMALL LETTER E

U+0065

COMBINING ACTUE ACCENT

U+0301

é

e

é

é

Character

let eAcute: Character = "\u{E9}"                         // é
let combinedEAcute: Character = "\u{65}\u{301}"          // e 后面加上  ́
// eAcute 是 é, combinedEAcute 是 é

Character

Character

let precomposed: Character = "\u{D55C}"                  // 한
let decomposed: Character = "\u{1112}\u{1161}\u{11AB}"   // ᄒ, ᅡ, ᆫ
// precomposed 是 한, decomposed 是 한

COMBINING ENCLOSING CIRCLE

U+20DD

Character

let enclosedEAcute: Character = "\u{E9}\u{20DD}"
// enclosedEAcute 是 é⃝

Character

REGIONAL INDICATOR SYMBOL LETTER U

U+1F1FA

REGIONAL INDICATOR SYMBOL LETTER S

U+1F1F8

let regionalIndicatorForUS: Character = "\u{1F1FA}\u{1F1F8}"

计算字符数量 (Counting Characters)

Character

characters

count

let unusualMenagerie = "Koala , Snail , Penguin , Dromedary "
print("unusualMenagerie has \(unusualMenagerie.characters.count) characters")
// 打印输出 "unusualMenagerie has 36 characters"

Character

cafe

COMBINING ACTUE ACCENT

U+0301

4

é

e

var word = "cafe"
print("the number of characters in \(word) is \(word.characters.count)")
// 打印输出 "the number of characters in cafe is 4"

word += "\u{301}"    // COMBINING ACUTE ACCENT, U+0301

print("the number of characters in \(word) is \(word.characters.count)")
// 打印输出 "the number of characters in café is 4"

characters

characters

NSString

length

NSString

length

NSString

length

String

utf16Count

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

字符串索引 (String Indices)

String

String.Index

Character

Character

String

startIndex

String

Character

endIndex

Character

endIndex

String

startIndex

endIndex

String

index(before:)

index(after:)

index(_:offsetBy:)

index(before:)

index(after:)

String

Character

let greeting = "Guten Tag!"
greeting[greeting.startIndex]
// G
greeting[greeting.index(before: greeting.endIndex)]
// !
greeting[greeting.index(after: greeting.startIndex)]
// u
let index = greeting.index(greeting.startIndex, offsetBy: 7)
greeting[index]
// a

Character

greeting[greeting.endIndex] // error
greeting.index(after: endIndex) // error

characters

indices

Range

for index in greeting.characters.indices {
print("\(greeting[index]) ", terminator: "")
}
// 打印输出 "G u t e n   T a g ! "

startIndex

endIndex

index(before:)

index(after:)

index(_:offsetBy:)

Collection

String

Array

Dictionary

Set

插入和删除 (Inserting and Removing)

insert(_:atIndex:)

insert(contentsOf:at:)

var welcome = "hello"
welcome.insert("!", at: welcome.endIndex)
// welcome 变量现在等于 "hello!"

welcome.insert(contentsOf:" there".characters, at: welcome.index(before: welcome.endIndex))
// welcome 变量现在等于 "hello there!"

remove(at:)

removeSubrange(_:)

welcome.remove(at: welcome.index(before: welcome.endIndex))
// welcome 现在等于 "hello there"

let range = welcome.index(welcome.endIndex, offsetBy: -6)..<welcome.endIndex
welcome.removeSubrange(range)
// welcome 现在等于 "hello"

insert(_:at:)

insert(contentsOf:at:)

remove(at:)

removeSubrange(_:)

RangeReplaceableCollection

String

Array

Dictionary

Set

比较字符串 (Comparing Strings)

字符串/字符相等 (String and Character Equality)

==

!=

let quotation = "We're a lot alike, you and I."
let sameQuotation = "We're a lot alike, you and I."
if quotation == sameQuotation {
print("These two strings are considered equal")
}
// 打印输出 "These two strings are considered equal"

LATIN SMALL LETTER E WITH ACUTE

U+00E9

LATIN SMALL LETTER E

U+0065

COMBINING ACUTE ACCENT

U+0301

é

// "Voulez-vous un café?" 使用 LATIN SMALL LETTER E WITH ACUTE
let eAcuteQuestion = "Voulez-vous un caf\u{E9}?"

// "Voulez-vous un café?" 使用 LATIN SMALL LETTER E and COMBINING ACUTE ACCENT
let combinedEAcuteQuestion = "Voulez-vous un caf\u{65}\u{301}?"

if eAcuteQuestion == combinedEAcuteQuestion {
print("These two strings are considered equal")
}
// 打印输出 "These two strings are considered equal"

LATIN CAPITAL LETTER A

U+0041

A

CYRILLIC CAPITAL LETTER A

U+0410

A

let latinCapitalLetterA: Character = "\u{41}"

let cyrillicCapitalLetterA: Character = "\u{0410}"

if latinCapitalLetterA != cyrillicCapitalLetterA {
print("These two characters are not equivalent")
}
// 打印 "These two characters are not equivalent"

前缀/后缀相等 (Prefix and Suffix Equality)

hasPrefix(_:)

hasSuffix(_:)

String

let romeoAndJuliet = [
"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"
]

hasPrefix(_:)

var act1SceneCount = 0
for scene in romeoAndJuliet {
if scene.hasPrefix("Act 1 ") {
act1SceneCount += 1
}
}
print("There are \(act1SceneCount) scenes in Act 1")
// 打印输出 "There are 5 scenes in Act 1"

hasSuffix(_:)

var mansionCount = 0
var cellCount = 0
for scene in romeoAndJuliet {
if scene.hasSuffix("Capulet's mansion") {
mansionCount += 1
} else if scene.hasSuffix("Friar Lawrence's cell") {
cellCount += 1
}
}
print("\(mansionCount) mansion scenes; \(cellCount) cell scenes")
// 打印输出 "6 mansion scenes; 2 cell scenes"

hasPrefix(_:)

hasSuffix(_:)

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

编码格式

代码单元

for-in

Character

utf8

utf16

unicodeScalars

D

o

g

‼

DOUBLE EXCLAMATION MARK

U+203C

let dogString = "Dog‼"

UTF-8 表示

String

utf8

UTF-8

String.UTF8View

UTF8View

UInt8

UInt8

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

codeUnit

68

111

103

D

o

g

codeUnit

226

128

188

DOUBLE EXCLAMATION MARK

codeUnit

240

159

144

182

DOG FACE

UTF-16 表示

String

utf16

UTF-16

String.UTF16View

UTF16View

UInt16

UInt16

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

codeUnit

68

111

103

D

o

g

codeUnit

8252

203C

DOUBLE EXCLAMATION MARK

U+203C

codeUnit

55357

56374

DOG FACE

U+D83D

55357

U+DC36

56374

Unicode 标量表示 (Unicode Scalars Representation)

String

unicodeScalars

UnicodeScalarView

UnicodeScalarView

UnicodeScalar

UnicodeScalar

UnicodeScalar

value

UInt32

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

UnicodeScalar

68

111

103

value

D

o

g

codeUnit

8252

203C

DOUBLE
EXCLAMATION MARK

U+203C

UnicodeScalar

value

128054

1F436

DOG FACE

U+1F436

value

UnicodeScalar

String

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