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：
Swift用来写iOS和OS X程序。（估计也不会支持其它屌丝系统）
Swift吸取了C和Objective-C的优点，且更加强大易用。
Swift可以使用现有的Cocoa和Cocoa Touch框架。
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。
- println("Hello, world")
变量与常量
Swift使用var声明变量，let声明常量。
- 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：
- 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）：
- let label = "The width is "
- let width = 94
- let widthLabel = label + String(width)
字符串格式化
Swift使用\(item)的形式进行字符串格式化：
- let apples = 3
- let oranges = 5
- let appleSummary = "I have \(apples) apples."
- let appleSummary = "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）：
- 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：
- 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
- }
- }
可空类型
结合if和let，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。
- 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：
- 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：
- 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：
- var n = 2
- while
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