Question

苹果的编程语言 Swift 是用什么开发的

Answer 1

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 width = 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." }