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Swift基本概念

admin

11月 28, 2021

Hello, world

  类似于脚本语言,下面的代码即是一个完整的 Swift 程序。

1 println ("Hello, world")

变量与常量

  Swift 使用var声明变量,let声明常量。

1 var myVariable = 42
2 myVariable = 50
3 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:

1 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):

1 let label = "The width is "
2 let width = 94
3 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:

1 let apples = 3
2 let oranges = 5
3 let appleSummary = "I have (apples) apples."
4 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):

1 var shoppingList = ["catfish", "water", "tulips", "blue paint"]
2 shoppingList[1] = "bottle of water" var occupations = [
3     "Malcolm": "Captain",
4     "Kaylee": "Mechanic",
5 ]
6 occupations["Jayne"] = "Public Relations"

一般使用初始化器(initializer)语法创建空数组和空字典:

1 let emptyArray = String[]()
2 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。

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