标签：swift ios objective-c swift简介 the swift programmin
2014年06月03日凌晨，Apple刚刚发布了Swift编程语言，本文从其发布的书籍《The Swift Programming Language》中摘录和提取而成。希望对各位的iOS&OSX开发有所帮助。Swift使用var声明变量，let声明常量。
var myVariable = 42 myVariable = 50 let myConstant = 42
let explicitDouble : Double = 70
let label = "The width is " let width = 94 let width = label + String(width)
let apples = 3 let oranges = 5 let appleSummary = "I have \(apples) apples." let appleSummary = "I have \(apples + oranges) pieces of fruit."
var shoppingList = ["catfish", "water", "tulips", "blue paint"] shoppingList[1] = "bottle of water" var occupations = [ "Malcolm": "Captain", "Kaylee": "Mechanic", ] occupations["Jayne"] = "Public Relations"
let emptyArray = String[]() let emptyDictionary = Dictionary<String, Float>()
概览
Swift的条件语句包含if和switch，循环语句包含for-in、for、while和do-while，循环/判断条件不需要括号，但循环/判断体（body）必需括号：
let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
if score > 50 {
teamScore += 3
} else {
teamScore += 1
}
}var optionalString: String? = "Hello"
optionalString == nil
var optionalName: String? = "John Appleseed"
var gretting = "Hello!"
if let name = optionalName {
gretting = "Hello, \(name)"
}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."
}
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
}
}
}
largestvar n = 2
while n < 100 {
n = n * 2
}
n
var m = 2
do {
m = m * 2
} while m < 100
mvar firstForLoop = 0
for i in 0..3 {
firstForLoop += i
}
firstForLoop
var secondForLoop = 0
for var i = 0; i < 3; ++i {
secondForLoop += 1
}
secondForLoop函数
Swift使用func关键字声明函数：
func greet(name: String, day: String) -> String {
return "Hello \(name), today is \(day)."
}
greet("Bob", "Tuesday")func getGasPrices() -> (Double, Double, Double) {
return (3.59, 3.69, 3.79)
}
getGasPrices()func sumOf(numbers: Int...) -> Int {
var sum = 0
for number in numbers {
sum += number
}
return sum
}
sumOf()
sumOf(42, 597, 12)func returnFifteen() -> Int {
var y = 10
func add() {
y += 5
}
add()
return y
}
returnFifteen()func makeIncrementer() -> (Int -> Int) {
func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
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)numbers.map({
(number: Int) -> Int in
let result = 3 * number
return result
})numbers.map({ number in 3 * number })sort([1, 5, 3, 12, 2]) { $0 > $1 }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：
class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}var shape = Shape() shape.numberOfSides = 7 var shapeDescription = shape.simpleDescription()
class NamedShape {
var numberOfSides: Int = 0
var name: String
init(name: String) {
self.name = name
}
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}Swift支持继承和多态（override父类方法）：
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()为了简化代码，Swift引入了属性（property），见下面的perimeter字段：
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.sideLengthclass 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.sideLengthSwift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：
class Counter {
var count: Int = 0
func incrementBy(amount: Int, numberOfTimes times: Int) {
count += amount * times
}
}
var counter = Counter()
counter.incrementBy(2, numberOfTimes: 7)let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square") let sideLength = optionalSquare?.sideLength
枚举
使用enum创建枚举——注意Swift的枚举可以关联方法：
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:
return "queen"
case .King:
return "king"
default:
return String(self.toRaw())
}
}
}
let ace = Rank.Ace
let aceRawValue = ace.toRaw()if let convertedRank = Rank.fromRaw(3) {
let threeDescription = convertedRank.simpleDescription()
}enum Suit {
case Spades, Hearts, Diamonds, Clubs
func simpleDescription() -> String {
switch self {
case .Spades:
return "spades"
case .Hearts:
return "hearts"
case .Diamonds:
return "diamonds"
case .Clubs:
return "clubs"
}
}
}
let hearts = Suit.Hearts
let heartsDescription = hearts.simpleDescription()enum ServerResponse {
case Result(String, String)
case Error(String)
}
let success = ServerResponse.Result("6:00 am", "8:09 pm")
let failure = ServerResponse.Error("Out of cheese.")
switch success {
case let .Result(sunrise, sunset):
let serverResponse = "Sunrise is at \(sunrise) and sunset is at \(sunset)."
case let .Error(error):
let serverResponse = "Failure... \(error)"
}struct Card {
var rank: Rank
var suit: Suit
func simpleDescription() -> String {
return "The \(rank.simpleDescription()) of \(suit.simpleDescription())"
}
}
let threeOfSpades = Card(rank: .Three, suit: .Spades)
let threeOfSpadesDescription = threeOfSpades.simpleDescription()协议
Swift使用protocol定义协议：
protocol ExampleProtocol {
var simpleDescription: String { get }
mutating func adjust()
}class SimpleClass: ExampleProtocol {
var simpleDescription: String = "A very simple class."
var anotherProperty: Int = 69105
func adjust() {
simpleDescription += " Now 100% adjusted."
}
}
var a = SimpleClass()
a.adjust()
let aDescription = a.simpleDescription
struct SimpleStructure: ExampleProtocol {
var simpleDescription: String = "A simple structure"
mutating func adjust() {
simpleDescription += " (adjusted)"
}
}
var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescriptionextension Int: ExampleProtocol {
var simpleDescription: String {
return "The number \(self)"
}
mutating func adjust() {
self += 42
}
}
7.simpleDescriptionfunc repeat<ItemType>(item: ItemType, times: Int) -> ItemType[] {
var result = ItemType[]()
for i in 0..times {
result += item
}
return result
}
repeat("knock", 4)// Reimplement the Swift standard library's optional type
enum OptionalValue<T> {
case None
case Some(T)
}
var possibleInteger: OptionalValue<Int> = .None
possibleInteger = .Some(100)func anyCommonElements <T, U where T: Sequence, U: Sequence, T.GeneratorType.Element: Equatable, T.GeneratorType.Element == U.GeneratorType.Element> (lhs: T, rhs: U) -> Bool {
for lhsItem in lhs {
for rhsItem in rhs {
if lhsItem == rhsItem {
return true
}
}
}
return false
}
anyCommonElements([1, 2, 3], [3])
注意：下面的感受纯属个人意见，仅供参考。
大杂烩
尽管我接触Swift不足两小时，但很容易看出Swift吸收了大量其它编程语言中的元素，这些元素包括但不限于：
属性（Property）、可空值（Nullable type）语法和泛型（Generic Type）语法源自C#。
格式风格与Go相仿（没有句末的分号，判断条件不需要括号）。
Python风格的当前实例引用语法（使用self）和列表字典声明语法。
Haskell风格的区间声明语法（比如1..3，1...3）。
协议和扩展源自Objective-C（自家产品随便用）。
枚举类型很像Java（可以拥有成员或方法）。
class和struct的概念和C#极其相似。
注意这里不是说Swift是抄袭——实际上编程语言能玩的花样基本就这些，况且Swift选的都是在我看来相当不错的特性。
而且，这个大杂烩有一个好处——就是任何其它编程语言的开发者都不会觉得Swift很陌生——这一点很重要。
拒绝隐式（Refuse implicity）
Swift去除了一些隐式操作，比如隐式类型转换和隐式方法重载这两个坑，干的漂亮。
Swift的应用方向
我认为Swift主要有下面这两个应用方向：
教育
我指的是编程教育。现有编程语言最大的问题就是交互性奇差，从而导致学习曲线陡峭。相信Swift及其交互性极强的编程环境能够打破这个局面，让更多的人——尤其是青少年，学会编程。
这里有必要再次提到Brec Victor的Inventing on Principle，看了这个视频你就会明白一个交互性强的编程环境能够带来什么。
应用开发
现有的iOS和OS X应用开发均使用Objective-C，而Objective-C是一门及其繁琐（verbose）且学习曲线比较陡峭的语言，如果Swift能够提供一个同现有Obj-C框架的简易互操作接口，我相信会有大量的程序员转投Swift；与此同时，Swift简易的语法也会带来相当数量的其它平台开发者。
总之，上一次某家大公司大张旗鼓的推出一门编程语言及其编程平台还是在2000年（微软推出C#），将近15年之后，苹果推出Swift——作为开发者，我很高兴能够见证一门编程语言的诞生。
参照地址：http://zh.lucida.me/blog/an-introduction-to-swift/
来自苹果的编程语言——Swift简介【整理】,布布扣,bubuko.com
标签：swift ios objective-c swift简介 the swift programmin
原文地址：http://blog.csdn.net/u011439689/article/details/28402803
