Swift语言概览-自己在Xcode6动手写1

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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

// Playground - noun: a place where people can play

import Cocoa

var str = "Hello, playground"
var str1 = "Hello Wrold!!!"
var str2 = "O(∩_∩)O哈哈~"

// Hello, world
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
let explicitDouble : Double = 70

// Swift 不支持隐式 类型转换 （所以需要显式类型转换）
let label = "The width is"
let width = 94
let width1 = label + String(width)

// 使用 \(item) 的形式进行 字符串格式化
let apples = 3
let orages = 5
let sum = "I have \(apples) apples."
let sum1 = "I have \(apples + orages) pieces of fruit."

// 数组和字典
// Swift 使用[] 操作符声明 数组（array）和字典 （dictionary）
var listArr = ["fish","water","apple","rice"]
listArr[1] = "bottle of water"

var dict = [
    "name": "melody",
    "age" : "26",

]
dict["sex"] = "female"

// 一般使用初始化器（initializer）语法创建空数组和空字典

let emptyArray = String[]()
let emptyDict = Dictionary<String, Float>()