• 设为首页
  • 点击收藏
  • 手机版
    手机扫一扫访问
    迪恩网络手机版
  • 关注官方公众号
    微信扫一扫关注
    公众号

[转]Swift简介-苹果最新的编程语言

原作者: [db:作者] 来自: [db:来源] 收藏 邀请
首先感谢原作者,主要内容是借鉴他的,参考链接
http://zh.lucida.me/blog/an-introduction-to-swift/

关于

这篇文章简要介绍了苹果于WWDC 2014发布的编程语言——Swift。

前言

在这里我认为有必要提一下Bret VictorInventing on Principle,Swift编程环境的大部分概念都源自于Bret这个演讲。

接下来进入正题。

Swift是什么?

Swift是苹果于WWDC 2014发布的编程语言,这里引用The Swift Programming Language的原话:

Swift is a new programming language for iOS and OS X apps that builds on the best of C and Objective-C, without the constraints of C compatibility.

Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible and more fun.

Swift’s clean slate, backed by the mature and much-loved Cocoa and Cocoa Touch frameworks, is an opportunity to imagine how software development works.

Swift is the first industrial-quality systems programming language that is as expressive and enjoyable as a scripting language.

简单的说:

  1. Swift用来写iOS和OS X程序。(估计也不会支持其它屌丝系统)
  2. Swift吸取了C和Objective-C的优点,且更加强大易用。
  3. Swift可以使用现有的Cocoa和Cocoa Touch框架。
  4. Swift兼具编译语言的高性能(Performance)和脚本语言的交互性(Interactive)。

Swift语言概览

基本概念

注:这一节的代码源自The Swift Programming Language中的A Swift Tour

Hello, world

类似于脚本语言,下面的代码即是一个完整的Swift程序。

1
println("Hello, world")

变量与常量

Swift使用var声明变量,let声明常量。

1
2
3
var myVariable = 42
myVariable = 50
let myConstant = 42

类型推导

Swift支持类型推导(Type Inference),所以上面的代码不需指定类型,如果需要指定类型:

1
let explicitDouble : Double = 70

Swift不支持隐式类型转换(Implicitly casting),所以下面的代码需要显式类型转换(Explicitly casting):

1
2
3
let label = "The width is "
let width = 94
let labelWidth = label + String(width)

字符串格式化

Swift使用\(item)的形式进行字符串格式化:

1
2
3
4
let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."

数组和字典

Swift使用[]操作符声明数组(array)和字典(dictionary):

1
2
3
4
5
6
7
8
var shoppingList = ["catfish", "water", "tulips", "blue paint"]
shoppingList[1] = "bottle of water"
var occupations = [
    "Malcolm": "Captain",
    "Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"

一般使用初始化器(initializer)语法创建空数组和空字典:

1
2
let emptyArray = String[]()
let emptyDictionary = Dictionary<String, Float>()

如果类型信息已知,则可以使用[]声明空数组,使用[:]声明空字典。

控制流

概览

Swift的条件语句包含ifswitch,循环语句包含for-inforwhiledo-while,循环/判断条件不需要括号,但循环/判断体(body)必需括号:

1
2
3
4
5
6
7
8
9
let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
    if score > 50 {
        teamScore += 3
    } else {
        teamScore += 1
    }
}

可空类型

结合iflet,可以方便的处理可空变量(nullable variable)。对于空值,需要在类型声明后添加?显式标明该类型可空。

1
2
3
4
5
6
7
8
var optionalString: String? = "Hello"
optionalString == nil
var optionalName: String? = "John Appleseed"
var gretting = "Hello!"
if let name = optionalName {
    gretting = "Hello, \(name)"
}

灵活的switch

Swift中的switch支持各种各样的比较操作:

1
2
3
4
5
6
7
8
9
10
11
let vegetable = "red pepper"
switch vegetable {
case "celery":
    let vegetableComment = "Add some raisins and make ants on a log."
case "cucumber", "watercress":
    let vegetableComment = "That would make a good tea sandwich."
case let x where x.hasSuffix("pepper"):
    let vegetableComment = "Is it a spicy \(x)?"
default:
    let vegetableComment = "Everything tastes good in soup."
}

其它循环

for-in除了遍历数组也可以用来遍历字典:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]
var largest = 0
for (kind, numbers) in interestingNumbers {
    for number in numbers {
        if number > largest {
            largest = number
        }
    }
}
largest

while循环和do-while循环:

1
2
3
4
5
6
7
8
9
10
11
var n = 2
while n < 100 {
    n = n * 2
}
n
var m = 2
do {
    m = m * 2
} while m < 100
m

Swift支持传统的for循环,此外也可以通过结合..(生成一个区间)和for-in实现同样的逻辑。

1
2
3
4
5
6
7
8
9
10
11
var firstForLoop = 0
for i in 0..3 {
    firstForLoop += i
}
firstForLoop
var secondForLoop = 0
for var i = 0; i < 3; ++i {
    secondForLoop += 1
}
secondForLoop

注意:Swift除了..还有.....生成前闭后开的区间,而...生成前闭后闭的区间。

函数和闭包

函数

Swift使用func关键字声明函数:

1
2
3
4
func greet(name: String, day: String) -> String {
    return "Hello \(name), today is \(day)."
}
greet("Bob", "Tuesday")

通过元组(Tuple)返回多个值:

1
2
3
4
func getGasPrices() -> (Double, Double, Double) {
    return (3.59, 3.69, 3.79)
}
getGasPrices()

支持带有变长参数的函数:

1
2
3
4
5
6
7
8
9
func sumOf(numbers: Int...) -> Int {
    var sum = 0
    for number in numbers {
        sum += number
    }
    return sum
}
sumOf()
sumOf(42, 597, 12)

函数也可以嵌套函数:

1
2
3
4
5
6
7
8
9
func returnFifteen() -> Int {
    var y = 10
    func add() {
        y += 5
    }
    add()
    return y
}
returnFifteen()

作为头等对象,函数既可以作为返回值,也可以作为参数传递:

1
2
3
4
5
6
7
8
func makeIncrementer() -> (Int -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
increment(7)
1
2
3
4
5
6
7
8
9
10
11
12
13
func hasAnyMatches(list: Int[], condition: Int -> Bool) -> Bool {
    for item in list {
        if condition(item) {
            return true
        }
    }
    return false
}
func lessThanTen(number: Int) -> Bool {
    return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches(numbers, lessThanTen)

闭包

本质来说,函数是特殊的闭包,Swift中可以利用{}声明匿名闭包:

1
2
3
4
5
numbers.map({
    (number: Int) -> Int in
    let result = 3 * number
    return result
    })

当闭包的类型已知时,可以使用下面的简化写法:

1
numbers.map({ number in 3 * number })

此外还可以通过参数的位置来使用参数,当函数最后一个参数是闭包时,可以使用下面的语法:

1
sort([1, 5, 3, 12, 2]) { $0 > $1 }

类和对象

创建和使用类

Swift使用class创建一个类,类可以包含字段和方法:

1
2
3
4
5
6
class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

创建Shape类的实例,并调用其字段和方法。

1
2
3
var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

通过init构建对象,既可以使用self显式引用成员字段(name),也可以隐式引用(numberOfSides)。

1
2
3
4
5
6
7
8
9
10
11
12
class NamedShape {
    var numberOfSides: Int = 0
    var name: String
    init(name: String) {
        self.name = name
    }
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

使用deinit进行清理工作。

继承和多态

Swift支持继承和多态(override父类方法):

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class Square: NamedShape {
    var sideLength: Double
    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSides = 4
    }
    func area() -> Double {
        return sideLength * sideLength
    }
    override func simpleDescription() -> String {
        return "A square with sides of length \(sideLength)."
    }
}
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()

注意:如果这里的simpleDescription方法没有被标识为override,则会引发编译错误。

属性

为了简化代码,Swift引入了属性(property),见下面的perimeter字段:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
class EquilateralTriangle: NamedShape {
    var sideLength: Double = 0.0
    init(sideLength: Double, name: String) {
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSides = 3
    }
    var perimeter: Double {
    get {
        return 3.0 * sideLength
    }
    set {
        sideLength = newValue / 3.0
    }
    }
    override func simpleDescription() -> String {
        return "An equilateral triagle with sides of length \(sideLength)."
    }
}
var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
triangle.perimeter
triangle.perimeter = 9.9
triangle.sideLength

注意:赋值器(setter)中,接收的值被自动命名为newValue

willSet和didSet

EquilateralTriangle的构造器进行了如下操作:

  1. 为子类型的属性赋值。
  2. 调用父类型的构造器。
  3. 修改父类型的属性。

如果不需要计算属性的值,但需要在赋值前后进行一些操作的话,使用willSetdidSet

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class TriangleAndSquare {
    var triangle: EquilateralTriangle {
    willSet {
        square.sideLength = newValue.sideLength
    }
    }
    var square: Square {
    willSet {
        triangle.sideLength = newValue.sideLength
    }
    }
    init(size: Double, name: String) {
        square = Square(sideLength: size, name: name)
        triangle = EquilateralTriangle(sideLength: size, name: name)
    }
}
var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
triangleAndSquare.square.sideLength
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
triangleAndSquare.triangle.sideLength

从而保证trianglesquare拥有相等的sideLength

调用方法

Swift中,函数的参数名称只能在函数内部使用,但方法的参数名称除了在内部使用外还可以在外部使用(第一个参数除外),例如:

1
2
3
4
5
6
7
8
class Counter {
    var count: Int = 0
    func incrementBy(amount: Int, numberOfTimes times: Int) {
        count += amount * times
    }
}
var counter = Counter()
counter.incrementBy(2, numberOfTimes: 7)

注意Swift支持为方法参数取别名:在上面的代码里,numberOfTimes面向外部,times面向内部。

?的另一种用途

使用可空值时,?可以出现在方法、属性或下标前面。如果?前的值为nil,那么?后面的表达式会被忽略,而原表达式直接返回nil,例如:

1
2
3
let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional 
square")
let sideLength = optionalSquare?.sideLength

optionalSquarenil时,sideLength属性调用会被忽略。

枚举和结构

枚举

使用enum创建枚举——注意Swift的枚举可以关联方法:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
enum Rank: Int {
    case Ace = 1
    case Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten
    case Jack, Queen, King
        func simpleDescription() -> String {
        switch self {
            case .Ace:
                return "ace"
            case .Jack:
                return "jack"
            case .Queen:

                      

鲜花

握手

雷人

路过

鸡蛋
该文章已有0人参与评论

请发表评论

全部评论

专题导读
热门推荐
热门话题
阅读排行榜

扫描微信二维码

查看手机版网站

随时了解更新最新资讯

139-2527-9053

在线客服(服务时间 9:00~18:00)

在线QQ客服
地址:深圳市南山区西丽大学城创智工业园
电邮:jeky_zhao#qq.com
移动电话:139-2527-9053

Powered by 互联科技 X3.4© 2001-2213 极客世界.|Sitemap