Swift 类和结构体

结构体和类的声明以及实例化

import UIKit

// 结构体和类的声明
struct Resolution {
    var width = 0
    var height = 0
}

class VideoMode {
    var resolution = Resolution()
    var interlaced = false
    var frameRate = 0.0
    var name: String?
}


// 结构体和类的实例化
let someResolution = Resolution()
let someVideoMode = VideoMode()

属性的访问

// 访问属性
print("The width of someResolution is \(someResolution.width)")

print("The width of someVideMode is \(someVideoMode.resolution.width)")

someVideoMode.resolution.width = 1280
print("The width of someVideMode is now \(someVideoMode.resolution.width)")

console log 如下

类和结构体属性访问.png

结构体是值拷贝

// 结构体是值拷贝
let vga = Resolution(width: 640, height: 480)
var cinema = vga
cinema.height = 960

print("cinema is now \(cinema.height) pixels height")
print("vga is still \(vga.height) pixels height")

console log 如下

结构体是值拷贝.png

枚举也是值拷贝

// 枚举也是值拷贝
enum CompassPoint {
    case notth, south, east, west
}

var currentDirection = CompassPoint.west
let rememberedDirection = currentDirection
currentDirection = .east
if rememberedDirection == .west {
    print("The remembered direction is still .west")
}

console log 如下

枚举也是值拷贝.png

类是引用类型

// 类是引用类型
let tenEighty = VideoMode()
tenEighty.resolution = vga
tenEighty.interlaced = true
tenEighty.name = "1080i"
tenEighty.frameRate = 25.0

let alsoTenEighty = tenEighty
alsoTenEighty.frameRate = 30.0

print("The frameRate property of tenEighty is now \(tenEighty.frameRate)")

console log 如下

类是引用类型.png

=== 或者 !== 运算符

// === 运算符 或者 !==
if tenEighty === alsoTenEighty {
    print("tenEighty and alsoTenEighty refre to the same VideoMode instance")
}

console log 如下

类同一个引用的运算符.png

注意：在Swift 中String,Array,Dictionary 都是作为结构体实现的，也就是在赋值时以及作为函数参数时都是进行的值拷贝

Swift 类和结构体

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