苹果编程语言Swift中文教程:Swift简介

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这篇文章简要介绍了iPhoneiPhoneiPhoneiPhone于WWDC 2014发布的编程语言——Swift。

Swift是那些?

Swift是iPhoneiPhoneiPhoneiPhone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线程池池池。(估计但会 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可不还可以 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:相似于于 节的代码源自The Swift Programming Language中的A Swift Tour。

Hello, world

相似于于脚本语言,下面的代码即是三个 多多 删剪的Swift线程池池池。

  • 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 = 1000
  • let myConstant = 42

类型推导

Swift支持类型推导(Type Inference),很多很多顶端的代码不需指定类型,由于还要指定类型:

  • let explicitDouble : Double = 70

Swift不支持隐式类型转换(Implicitly casting),很多很多下面的代码还要显式类型转换(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>()

由于类型信息已知,则可不还可以 使用[]声明空数组,使用[:]声明空字典。

控制流

概览

Swift的条件句子含高if和switch,循环句子含高for-in、for、while和do-while,循环/判断条件不还要括号,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 > 1000 {

            teamScore += 3

        } else {

            teamScore += 1

        }

    }

可空类型

结合if和let,可不还可以 方便的外理可空变量(nullable variable)。对于空值,还要在类型声明后上加?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除了遍历数组也可不还可以 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 n < 1000 {
  •     n = n * 2
  • }
  • n
  • var m = 2
  • do {
  •     m = m * 2
  • } while m < 1000
  • m

Swift支持传统的for循环,此外也可不还可以 通过结合..(生成三个 多多 区间)和for-in实现同样的逻辑。

  • var firstForLoop = 0
  • for i in 0..3 {
  •     firstForLoop += i
  • }
  • firstForLoop
  • var secondForLoop = 0
  • for var i = 0; i < 3; ++i {
  •     secondForLoop += 1
  • }

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。

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