Swift5.x入门07--枚举

枚举的基本使用

import UIKit

enum Direction {
    case north
    case south
    case west
    case east
}

enum Direction1 {
    case north,south,west,east
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        var dir = Direction.north
        dir = Direction.west
        //枚举类型可以省略
        dir = .south
        print(dir)
        
        switch dir {
        case .north:
            print("north")
        case .south:
            print("south")
        case .west:
            print("west")
        default:
            print("east")
        }
    }
}

关联值

  • 关联值:将枚举的成员值其他类型的数值关联存储在一起的值,称之为枚举的关联值
import UIKit

enum Score{
    case points(Int)
    case grade(Character)
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        var score = Score.points(100)
        score = Score.grade("A")
        print("score = \(score)")
        
        switch score {
        case let .points(i):
            print("point = \(i)")
        case let .grade(i):
            print("grade = \(i)")
        }
    }
}
  • Score枚举有两种类型,一种是分值表示,另一种是字符表示;
  • case let .points(i):表示当枚举变量scorecase points(Int)枚举类型时,取出此时枚举变量的关联值,赋值给常量i,注意let是用来修饰接收 枚举关联值 的常量i的;
enum Date {
    case digit(year: Int,month: Int,day: Int)
    case string(String)
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        var date = Date.digit(year: 2021, month: 7, day: 29)
        date = Date.string("2020-09-24")
        
        switch date {
        case .digit(let year, let month, let day):
            print("\(year) - \(month) - \(day)")
        case let .string(value):
            print("\(value)")
        }
    }
}
  • 日期的表示有两种类型的枚举;
enum Password {
    case number(Int,Int,Int,Int)
    case gersure(String)
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        var password = Password.number(1, 2, 3, 4)
        password = Password.gersure("123456789")
        
        switch password {
        case let .number(n1, n2, n3, n4):
            print("number is",n1,n2,n3,n4)
        case let .gersure(value):
            print(value)
        }
    }
}
  • 密码的表示有两种类型;

原始值

  • 枚举成员可以使用相同类型的默认值预先关联,这个默认值叫做原始值;
enum Grade : String{
    case perfect = "A"
    case great = "B"
    case good = "C"
    case bad = "D"
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        print(Grade.perfect.rawValue) //A
        print(Grade.great.rawValue) //B
        print(Grade.good.rawValue) //C
        print(Grade.bad.rawValue) //D
    }
}
  • rawValue可获取枚举成员预先设置的原始值;

隐式原始值

enum Direction2 : String {
    case north,south,west,east
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        print(Direction2.north.rawValue) //north
        print(Direction2.south.rawValue) //south
        print(Direction2.west.rawValue) //west
        print(Direction2.east.rawValue) //east
    }
}
  • 上面这种写法,会默认给对应的枚举类型设置原始值,原始值与枚举类型的名称相同;
enum Season : Int {
    case spring,summer,autum,winter
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        print(Season.spring.rawValue) //0
        print(Season.summer.rawValue) //1
        print(Season.autum.rawValue)  //2
        print(Season.winter.rawValue) //3
    }
}
  • Int类型的枚举原始值,默认从0开始递增;

递归枚举

indirect enum MathOpeartion {
    case number(Int)
    case sum(MathOpeartion,MathOpeartion)
    case diff(MathOpeartion,MathOpeartion)
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let n1 = MathOpeartion.number(10)
        let n2 = MathOpeartion.number(20)
        let sum = MathOpeartion.sum(n1, n2)
        
        let result = calculate(sum)
        print(result)
    }
    
    func calculate(_ mathExpr: MathOpeartion) -> Int {
        switch mathExpr {
        case let .number(value):
            return value
        case let .sum(n1, n2):
            return calculate(n1) + calculate(n2)
        case let .diff(n1, n2):
            return calculate(n1) - calculate(n2)
        }
    }
}
  • indirect关键字表示当前枚举为递归枚举;

MemoryLayout

  • 获取数据类型占用的内存大小;
enum Season : Int {
    case spring,summer,autum,winter
}

enum Password {
    case number(Int,Int,Int,Int)
    case gersure(String)
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let a = 10
        print(MemoryLayout.size(ofValue: a)) //8
        print(MemoryLayout.stride(ofValue: a))//8
        print(MemoryLayout.alignment(ofValue: a))//8
        
        print(MemoryLayout.size)//1
        print(MemoryLayout.stride)//1
        print(MemoryLayout.alignment)//1

        print(MemoryLayout.size) //33
        print(MemoryLayout.stride) //40
        print(MemoryLayout.alignment) //8
    }
}
  • MemoryLayout.size():获取目标实际的内存大小;
  • MemoryLayout.stride():获取目标分配的内存大小,会使用内存对其算法;
  • MemoryLayout.alignment():获取内存对其参数;
  • Password枚举类型变量所占用的内存大小与其关联值相关,number类型有4个Int类型,占用32个字节点,额外的一个字节是用来区分gesure类型的,总共实际占33个字节,gesure是字符串类型,33个字节完全能存储字符串,此枚举感觉跟C语言中的共用体很相似;
  • Season枚举类型变量只占用一个字节,与原始值Int类型没什么关系,内存用一个字节就完全能区分Season枚举类型的所有枚举;

枚举变量的内存布局

最普通的情况:
  • 新建命令行项目,代码如下:
enum Season {
    case spring,summer,autum,winter
}

import Foundation

var a: Int = 10
a = 20

var season = Season.spring
season = Season.summer
season = Season.autum
print(season)
  • 当断点停在season = Season. summer所在行时,查看内存布局如下所示:
Snip20210730_50.png
  • Int类型变量a占用8个字节,枚举变量season占用一个字节;
  • 当断点停在season = Season.autum所在行时,内存布局如下:
Snip20210730_51.png
枚举使用原始值的情况,代码如下:
enum Season : Int{
    case spring = 2,summer,autum,winter
}

import Foundation

var a: Int = 10
a = 20

var season = Season.spring
season = Season.summer
season = Season.autum
print(season)
  • 当断点停在season = Season.summer所在行时,查看内存布局如下所示:
Snip20210730_52.png
  • 当断点停在season = Season.autum所在行时,内存布局如下:
    Snip20210730_53.png
  • 可以看出原始值是不会存储到枚举变量中的,不会影响枚举变量的内存布局;
枚举使用关联值的情况
enum TestEnum{
    case test1(Int,Int,Int)
    case test2(Int,Int)
    case test3(Int)
    case test4(Bool)
    case test5
}

import Foundation

var a: Int = 10
a = 20

print(MemoryLayout.size) //25
print(MemoryLayout.stride) //32
print(MemoryLayout.alignment) //8

var test = TestEnum.test1(1, 2, 3)
test = TestEnum.test2(4, 5)
test = TestEnum.test3(6)
test = TestEnum.test4(true)
test = TestEnum.test5
  • 当断点停在test = TestEnum.test2(4, 5)所在行,内存布局如下所示:
Snip20210730_55.png
  • 前面8个字节存储的是整型变量a的值;
  • 紧接着24个字节存储的是枚举变量test的三个关联值1,2,3,最后一个字节存储的是枚举类型的成员值,即枚举变量在枚举类型中的类型,值为0;
  • 当断点停在test = TestEnum.test3(6)所在行,内存布局如下所示:
Snip20210730_57.png
  • 前面8个字节存储的是整型变量a的值;
  • 紧接着24个字节存储的是枚举变量test的三个关联值4,5,0,最后一个字节存储的是枚举类型的成员值,即枚举变量在枚举类型中的类型,值为1;
  • 以此类推,就很容易推断出后面枚举变量在内存的中布局情况了;
  • 总结:
    • 当枚举变量中存在多个枚举类型时,枚举变量会单独占用一个字节,用来存储枚举变量在枚举中的成员值;如果只有一个枚举时,就不需要单独占用一个字节了;
    • N个字节存储关联值(N取占用内存最大的关联值),枚举中任何一个case的关联值都共用这N个字节,与C语言中的共用体类似;

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