<Swift 巩固笔记> 第9篇 结构体和类

类型定义的语法

通过struct定义结构体

struct SomeStruct {   
}

通过class定义类

class SomeClass {

}

定义一个结构体, 用于描述分辨率

width: 横向分辨率

height: 纵向分辨率

struct Resolution {

  var width = 0

  var height = 0

}

定义一个类, 用于描述显示器的某个特定视频模式

class VideoModel {

  var resolution = Resolution()

  var interlaced = false

  var frameRate = 0.0

  var name: String?
}

创建一个结构体的实例和一个类的实例

var someResolution = Resolution()

let someVideoModel = VideoModel()

结构体属性的访问

someResolution.width = 1280

someResolution.height = 960

print("the width is \(someResolution.width)")

print("the height is \(someResolution.height)")

类中的属性的访问

someVideoModel.resolution.width = 2560

someVideoModel.resolution.height = 1080

print("the width is \(someVideoModel.resolution.width)")

print("the height is \(someVideoModel.resolution.height)")

结构体类型的成员逐一构造器, 类实例没有默认的成员逐一构造器

let vga = Resolution(width: 640, height: 680)

结构体和枚举是值类型

值类型: 当它被赋值给一个变量, 常量或者传递给一个函数的时候, 其值会被拷贝

值类型有: 整型, 浮点型, 布尔型, 字符串, 数组, 字典

let hd = Resolution(width: 1920, height: 1080)
var cinema = hd

// 通过查看地址来证明结构体的赋值是值拷贝\
print("hd地址为: \(Unmanaged<AnyObject>.passUnretained(hd **as** AnyObject).toOpaque())")
print("cinema地址为: \(Unmanaged<AnyObject>.passUnretained(cinema **as** AnyObject).toOpaque())")

// 更改其中一个实例的值
cinema.width = 2048
print("the width of cinema is \(cinema.width)")
print("the width of hd is \(hd.width)")

枚举是值类型

enum CompassPoint {
  case north, south, east, west
  mutating func tunrNorth() {
		self = .north
  }
}

var currentDirection = CompassPoint.west

let rememberDirection = currentDirection

currentDirection.tunrNorth()

print("the current direction is \(currentDirection)")

print("the remember direction is \(rememberDirection)")

类是引用类型

引用类型在被赋值给一个变量, 常量或者传递给一个函数时, 其值不会被拷贝

let tenEighty = VideoModel()

tenEighty.resolution = hd

tenEighty.interlaced = true

tenEighty.name = "1080i"

tenEighty.frameRate = 25.0

相当于同一实例的两种叫法

let alsoTenEighty = tenEighty

alsoTenEighty.frameRate = 30

print("the frame rate is \(tenEighty.frameRate)")

恒等运算符 === !===

if tenEighty === alsoTenEighty {

  print("tenEighty and alsoTenEight are same")

} else {

  print("tenEighty and alsoTenEighty are different")

}