Swift

基于swift5.1写的

基础语法

输出

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print("Hello World")
  • 不用编写main函数,Swift将全局范围内的首句可执行代码作为程序入口

  • 一句代码尾部可以省略分号(;),多句代码写到同一行时必须用分号(;)隔开

  • var定义变量,let定义常量,编译器能自动推断出变量\常量的类型

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    let a = 10
    let b = 20
    var c = a + b
    c += 30
  • Playground可以快速预览代码效果,是学习语法的好帮手

  • Command + Shift + Enter:运行整个Playground

  • Shift + Enter:运行截止到某一行代码

注释

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// 单行注释

/*
多行注释
*/

/*
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/* 多行注释嵌套 */
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*/

常量

  • 只能赋值1次
  • 它的值不要求在编译时期确定,但使用之前必须赋值1次
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let age1 = 10
let age2: Int
age2 = 20

func getAge() -> Int {
return 30
}
let age3 = getAge()
  • 常量、变量在初始化之前,都不能使用
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let age: Int
var height: Int
print(age)
print(height)
  • 下面代码是错误的
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let age
age = 20

标识符

  • 标识符(比如常量名、变量名、函数名)几乎可以使用任何字符
  • 标识符不能以数字开头,不能包含空白字符、制表符、箭头等特殊字符
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func 🐂🍺() {
print("666")
}
🐂🍺()

let 👽 = "ET"
var 🥛 = "milk"

常用数据类型

  • 整数类型:Int8、Int16、Int32、Int64、UInt8、UInt16、UInt32、UInt64

  • 在32bit平台,Int等价于Int32,Int等价于Int64

  • 整数的最值:UInt8.max、Int16.min

  • 一般情况下,都是直接使用Int即可

  • 浮点类型:Float,32位,精度只有6位;Double,64位,精度至少15位

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let letFloat: Float = 30.0
let letDouble = 30.0

字面量

布尔

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let bool = true // 取反是false

字符串

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let string = "飞翔"

字符(可存储ASCII字符、Unicode字符)

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let character: Character = "🐶"

整数

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let intDecimal = 15 //十进制
let intBinary = 0b10001 // 二进制
let intOctal = 0o21 // 八进制
let intHexadecimal = 0x11 // 十六进制

整数和浮点数可以添加额外的零或者添加下划线来增强可读性 p100_00001_000_000.000_000_1000123.456

浮点数

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let doubleDecimal = 15.0 //十进制, 等价于1.25e2,0.0125等价于1.25e-2
let doubleHexadecimal1 = 0xFp2 // 十六进制, 意味着25×2^2,相当于十进制的60
let doubleHexadecimal2 = 0xFp-2 // 十六进制, 意味着25×2^-2,相当于十进制的3.75

数组

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let array = [1, 3, 5, 7, 9]

字典

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let dictionary = ["age": 18, "height": 168, "weight": 120]

类型转换

整数转换

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let int1: UInt16 = 2_000
let int2: UInt8 = 1
let int3 = int1 + UInt16(int2)

整数、浮点数转换

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let int = 3
let double = 0.14
let pi = Double(int) + double
let intPi = Int(pi)

字面量相加

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// 字面量可以直接相加,欣慰数字字面量本身没有明确类型
let result = 3 + 0.14

元组

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let http404Error = (404, "Not Found")
print("The status code is \(http404Error.0)")

let (statusCode, statusMessage) = http404Error
print("The status code is \(statusCode)")

let (justTheStatusCode, _) = http404Error

let http200Error = (statusCode: 200, description: "OK")
print("The status code is \(http200Error.statusCode)")

流程控制

if-else

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let age = 4
if age >= 22 {
print("Get married")
} else if age >= 18 {
print("Being a adult")
} else if age >= 7 {
print("Go to school")
} else {
print("Just a child")
}
  • if后面的条件可以省略小括号
  • 条件后边的大括号不可以省略
  • if后边的条件智能是Bool类型
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// 错误代码
let age = 1
if age {

}

while

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var num = 5
where num > 5 {
print("num is \(num)")
num -= 1
} //打印了5次
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var num = -1
repeat {
print("num is \(num)")
num -= 1
} while num > 0 //打印了1次
  • repeat-while 相当于C语言的do-while
  • 这里不用num–,是因为从Swift3开始,去除了自增(++),自减(–)运算符

for

闭区间运算符:a…b, a <= 取值 <= b

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let names = ["Anna", "Alex", "Brian", "Jack"]
for i in 0...3 {
print(names[i])
}
// Anna, Alex, Brian, Jack
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let names = ["Anna", "Alex", "Brian", "Jack"]
let range = 1...3
for i in range {
print(names[i])
}
// Alex, Brian, Jack
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let names = ["Anna", "Alex", "Brian", "Jack"]
let a = 1
let b = 2
for i in a...b {
print(name[i])
}
// Alex, Brian
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// i默认是let, 如果有需要可以声明为var
for var i in 1...3 {
i += 5
print(i)
}
// 6 7 8
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for _ i in 1...3 {
print("for")
}
// 打印了三次

半开区间运算符:a..<b, a <= 取值 < b

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for i in 1..<5 {
print(i)
}
// 1 2 3 4

区间运算符用在数组上

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let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names[0...3] {
print(name)
}
// Anna, Alex, Brian, Jack

单侧区间
让区间朝着一个方向尽可能的远

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let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names[2...] {
print(name)
}
// Brian, Jack
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for name in names[...2] {
print(name)
}
// Anna, Alex, Brian
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for name in names[..<2] {
print(name)
}
// Anna, Alex
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let range = ...5
range.contains(7) // false
range.contains(4) // true
range.contains(7-3) // true

区间类型

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let range1: ClosedRange<Int> = 1...3
let range2: Range<Int> = 1..<3
let range3: PartialRangeThrough<Int> = ...5

字符、字符串也能使用区间运算符,但默认不能用在for-in中

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let stringRange1 = "cc"..."ff" // ClosedRange<String> 
stringRange1.contains("cb") // false
stringRange1.contains("dz") // true
stringRange1.contains("fg") // false
let stringRange2 = "a"..."f"
stringRange2.contains("d") // true
stringRange2.contains("h") // false
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// \0到~囊括了所有可能要用到的ASCII字符
let characterRange: ClosedRange<Character> = "\0"..."~" characterRange.contains("G") // true

带间隔的区间值

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let hours = 11
let hourInterval = 2
// tickMark的取值:从4开始,累加2,不超过11
for tickMark in stride(from: 4, through: hours, by: hourInterval) {
print(tickMark)
} // 4 6 8 10

switch

  • case、default后面不能写大括号{}
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var number = 1
switch number {
case 1:
print("number is 1")
break case 2:
print("number is 2")
break
default:
print("number is other")
break
} // number is 1
  • 默认可以不写break,并不会贯穿到后面的条件
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var number = 1
switch number {
case 1:
print("number is 1")
case 2:
print("number is 2")
default:
print("number is other")
} // number is 1
  • 使用fallthrough可以实现贯穿效果
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var number = 1
switch number {
case 1:
print("number is 1")
fallthrough
case 2:
print("number is 2")
default:
print("number is other")
}
// number is 1
// number is 2
  • switch必须要保证能处理所有情况
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// 错误示范,编译器会报错;应该加上default
var number = 1
switch number {
case 1:
print("number is 1")
case 2:
print("number is 2")
}
  • case、default后面至少要有一条语句
  • 如果不想做任何事,加个break即可
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var number = 1
switch number {
case 1:
print("number is 1")
case 2:
print("number is 2")
default:
break
}
  • 如果能保证已处理所有情况,也可以不必使用default
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enum Answer { case right, wrong } 
let answer = Answer.right
switch answer {
case Answer.right:
print("right")
case Answer.wrong:
print("wrong")
}
// 由于已确定answer是Ansewer类型,因此可以省略Answer
switch answer {
case .right:
print("right")
case .wrong:
print("wrong")
}
  • switch也支持Character、String类型
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let string = "Jack"
switch string {
case "Jack":
fallthrough
case "Rose":
print("Right person")
default:
break
}
// Right person
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let character: Character = "a"
switch character {
case "a", "A":
print("The letter A")
default:
print("Not the letter A")
}
// The letter A
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switch string {
case "Jack", "Rose":
print("Right person")
default:
break
}
// Right person
  • 区间匹配、元组匹配
  • 可以使用下划线 _ 忽略某个值
  • 关于case匹配问题,属于模式匹配(Pattern Matching)的范畴,以后会再次详细展开讲解
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let count = 62
switch count {
case 0:
print("none")
case 1..<5:
print("a few")
case 5..<12:
print("several")
case 12..<100:
print("dozens of")
case 100..<1000:
print("hundreds of")
default:
print("many")
}
// dozens of
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let point = (1, 1)
switch point {
case (0, 0):
print("the origin")
case (_, 0):
print("on the x-axis")
case (0, _):
print("on the y-axis")
case (-2...2, -2...2):
print("inside the box")
default:
print("outside of the box") }
// inside the box
  • 值绑定 必要时 let也可以改为var
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let point = (2, 0)
switch point {
case (let x, 0):
print("on the x-axis with an x value of \(x)")
case (0, let y):
print("on the y-axis with a y value of \(y)")
case let (x, y):
print("somewhere else at (\(x), \(y))")
}
// on the x-axis with an x value of 2
  • where
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let point = (1, -1)
switch point {
case let (x, y) where x == y:
print("on the line x == y")
case let (x, y) where x == -y:
print("on the line x == -y")
case let (x, y):
print("(\(x), \(y)) is just some arbitrary point") }

// on the line x == -y
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// 将所有正数加起来
var numbers = [10, 20, -10, -20, 30, -30]
var sum = 0
for num in numbers where num > 0 { // 使用where来过滤num
sum += num
}
print(sum) // 60
  • 标签语句;指定跳出的循环层级
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outer: for i in 1...4 { 
for k in 1...4 {
if k == 3 {
continue outer
}
if i == 3 {
break outer
}
print("i == \(i), k == \(k)")
}
}

函数

函数的定义

  • 形参默认是let,也只能是let
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func pi() -> Double { 
return 3.14
}
func sum(v1: Int, v2: Int) -> Int {
return v1 + v2
}
sum(v1: 10, v2: 20)
  • 无返回值
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func sayHello() -> Void {
print("Hello")
}
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func sayHello() -> () { 
print("Hello")
}
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func sayHello() {
print("Hello")
}

隐式返回(Implicit Return)

  • 如果整个函数体是一个单一表达式,那么函数会隐式返回这个表达式
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func sum(v1: Int, v2: Int) -> Int { 
v1 + v2
}
sum(v1: 10, v2: 20) // 30

返回元组:实现多返回值

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func calculate(v1: Int, v2: Int) -> (sum: Int, difference: Int, average: Int) { 
let sum = v1 + v2
return (sum, v1 - v2, sum >> 1)
}
let result = calculate(v1: 20, v2: 10)
result.sum // 30
result.difference // 10
result.average // 15

函数的文档注释

参考官方文档

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/// 求和【概述】 
///
/// 将2个整数相加【更详细的描述】
///
/// - Parameter v1: 第1个整数
/// - Parameter v2: 第2个整数
/// - Returns: 2个整数的和
///
/// - Note:传入2个整数即可【批注】
///
func sum(v1: Int, v2: Int) -> Int {
v1 + v2
}

参数标签(Argument Label)

可以修改参数标签

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func goToWork(at time: String) {
print("this time is \(time)")
}
goToWork(at: "08:00")
// this time is 08:00

可以使用下划线_ 省略参数标签

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func sum(_ v1: Int, _ v2: Int) -> Int { 
v1 + v2
}
sum(10, 20)

默认参数值(Default Parameter Value)

参数可以有默认值

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func check(name: String = "nobody", age: Int, job: String = "none") {
print("name=\(name), age=\(age), job=\(job)")
}
check(name: "Jack", age: 20, job: "Doctor") // name=Jack, age=20, job=Doctor
check(name: "Rose", age: 18) // name=Rose, age=18, job=none
check(age: 10, job: "Batman") // name=nobody, age=10, job=Batman
check(age: 15) // name=nobody, age=15, job=none

C++的默认参数值有个限制:必须从右往左设置。由于Swift拥有参数标签,因此并没有此类限制
但是在省略参数标签时,需要特别注意,避免出错

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// 这里的middle不可以省略参数标签
func test(_ first: Int = 10, middle: Int, _ last: Int = 30) { } test(middle: 20)

可变参数(Variadic Parameter)

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func sum(_ numbers: Int...) -> Int { 
var total = 0
for number in numbers {
total += number
}
return total
}
sum(10, 20, 30, 40) // 100

一个函数最多只能有1个可变参数
紧跟在可变参数后面的参数不能省略参数标签

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// 参数string不能省略标签
func test(_ numbers: Int..., string: String, _ other: String) { }
test(10, 20, 30, string: "Jack", "Rose")

Swift自带的print函数

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/// - Parameters:
/// - items: Zero or more items to print.
/// - separator: A string to print between each item. The default is a single space (`" "`).
/// - terminator: The string to print after all items have been printed. The
/// default is a newline (`"\n"`).
public func print(_ items: Any..., separator: String = " ", terminator: String = "\n")
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print(1, 2, 3, 4, 5) // 1 2 3 4 5
print(1, 2, 3, 4, 5, separator: "_") // 1_2_3_4_5
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print("My name is Jake.", terminator: "") 
print("My age is 18.")
// My name is Jake.My age is 18.

输入输出参数(In-Out Parameter)

可以用inout定义一个输入输出参数:可以在函数内部修改外部实参的值

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func swapValues(_ v1: inout Int, _ v2: inout Int) { 
let tmp = v1
v1 = v2
v2 = tmp
}
var num1 = 10
var num2 = 20
swapValues(&num1, &num2)
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func swapValues(_ v1: inout Int, _ v2: inout Int) { 
(v1, v2) = (v2, v1)
}

可变参数不能标记为inout
inout参数不能有默认值
inout参数只能传入可以被多次赋值的
inout参数的本质是地址传递(引用传递)

函数重载(Function Overload)

  • 规则
    • 函数名相同
    • 参数个数不同 || 参数类型不同 || 参数标签不同
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func sum(v1: Int, v2: Int) -> Int { 
v1 + v2
}
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func sum(v1: Int, v2: Int, v3: Int) -> Int { 
v1 + v2 + v3
} // 参数个数不同
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func sum(v1: Double, v2: Int) -> Double {
v1 + Double(v2) } // 参数类型不同
} // 参数类型不同
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func sum(_ v1: Int, _ v2: Int) -> Int { 
v1 + v2
} //https://cdn.renchengqi.com/blog
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func sum(a: Int, b: Int) -> Int {
a+b
} // 参数标签不同
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sum(v1: 10, v2: 20) // 30 
sum(v1: 10, v2: 20, v3: 30) // 60
sum(v1: 10, v2: 20.0) // 30.0
sum(v1: 10.0, v2: 20) // 30.0
sum(10, 20) // 30
sum(a: 10, b: 20) // 30

返回值类型与函数重载无关

默认参数值和函数重载一起使用产生二义性时,编译器并不会报错(在C++中会报错)

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func sum(v1: Int, v2: Int) -> Int { 
v1 + v2
}
func sum(v1: Int, v2: Int, v3: Int = 10) -> Int {
v1 + v2 + v3
}
// 会调用sum(v1: Int, v2: Int)
sum(v1: 10, v2: 20)

可变参数、省略参数标签、函数重载一起使用产生二义性时,编译器有可能会报错

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func sum(v1: Int, v2: Int) -> Int { 
v1 + v2
}
https://cdn.renchengqi.com/blog
func sum(_ v1: Int, _ v2: Int) -> Int {
v1 + v2
}

func sum(_ numbers: Int...) -> Int { var total = 0
for number in numbers {
total += number
}
return total
}
// error: ambiguous use of 'sum'
sum(10, 20)

内联函数

  • 如果开启了编译器优化(Release模式默认会开启优化),编译器会自动将某些函数变成内联函数 p将函数调用展开成函数体

  • 哪些函数不会被自动内联?

    • 函数体比较长
    • 包含递归调用
    • 包含动态派发

@inline

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// 永远不会被内联(即使开启了编译器优化) 
@inline(never) func test() {
print("test")
}
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// 开启编译器优化后,即使代码很长,也会被内联(递归调用函数、动态派发的函数除外) 
@inline(__always) func test() {
print("test")
}

在Release模式下,编译器已经开启优化,会自动决定哪些函数需要内联,因此没必要使用@inline

函数类型(Function Type)

每一个函数都是有类型的,函数类型由形式参数类型、返回值类型组成

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func test() { } // () -> Void 或者 () -> ()
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func sum(a: Int, b: Int) -> Int { 
a+b
} // (Int, Int) -> Int
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// 定义变量
var fn: (Int, Int) -> Int = sum
fn(2, 3) // 5,调用时不需要参数标签

函数类型作为函数参数

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func sum(v1: Int, v2: Int) -> Int { 
v1 + v2
}
func difference(v1: Int, v2: Int) -> Int {
v1 - v2
}
func printResult(_ mathFn: (Int, Int) -> Int, _ a: Int, _ b: Int) {
print("Result: \(mathFn(a, b))")
}
printResult(sum, 5, 2) // Result: 7
printResult(difference, 5, 2) // Result: 3

函数类型作为函数返回值

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func next(_ input: Int) -> Int { 
input + 1
}
func previous(_ input: Int) -> Int {
input - 1
}
func forward(_ forward: Bool) -> (Int) -> Int {
forward ? next : previous
}
forward(true)(3) // 4
forward(false)(3) // 2

返回值是函数类型的函数,叫做高阶函数(Higher-Order Function)

函数别名(typealias)

typealias用来给类型起别名

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typealias Byte = Int8
typealias Short = Int16
typealias Long = Int64
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typealias Date = (year: Int, month: Int, day: Int) func test(_ date: Date) {
print(date.0)
print(date.year)
}
test((2011, 9, 10))

按照Swift标准库的定义,Void就是空元组()

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public typealias Void = ()

typealias IntFn = (Int, Int) -> Int
func difference(v1: Int, v2: Int) -> Int {
v1 - v2
}
let fn: IntFn = difference
fn(20, 10) // 10
func setFn(_ fn: IntFn) { } setFn(difference)
func getFn() -> IntFn {
difference
}