println ("hello,world ")

使用 let 来声明常量,使用 var 来声明变量 。一个常量的值在编译时并不需要获取,但是你
只能为它赋值一次。也就是说你可以用常量来表示这样一个值:你只需要决定一次,但是需 要使用很多次。

var myV ariab le = 42
myVariable = 50
let myC onsta nt = 42

let implictiInteger = 70
let inlicitDouble = 70.0
let explicitDouble : Double = 70

let label = "The width is"
let width = 94
let widthLabel = label + String(width)

let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) appl es."
let fruitSummary = "I have \(apples + oranges) piec es of frui t."

var shoppingList = [" catfi sh","wate r"," tulip s"," blue paint "]
var occupations = ["Malcolm": "Captain","Kaylee": "Mechanic"]
occupations[ "Jayne"] = "Pu blic Relat ions"

要创建一个空数组或者字典,使用初始化语法。

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

如果类型信息可以被推断出来,你可以用[]和[:]来创建空数组和空字典——就像你声明变 量
或者给函数传参数的时候一样。

shoppingList = [] // 去逛街并买点东西

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