枚举

• 关联值: 枚举的成员值和其他类型的值关联储存,存储在枚举变量中

enum Date {
    
    case digit(year: Int, month: Int, day: Int)
    case string(String)
}


var date = Date.digit(year: 2019, month: 12, day: 31)
date = .string("2019-12-12")

switch date {
case .digit(let year, let month, var day):
    day = 10
    print(year, month, day)
case let .string(value):
    print(value)
}

• 原始值: 枚举成员使用相同的默认值预先对应，这个默认值是原始值。原始值没有存储在枚举变量中

enum Grade: String {
    case perfect = "A"
    case great = "B"
    case good = "C"
}

var grade = Grade.good

print(grade)
print(grade.rawValue)
print(Grade.perfect.rawValue)

//隐式原始值: 如果枚举的原始值类型是Int、String，Swift 会自动分配原始值。(Int: 从0开始按顺序给枚举成员原始值。String: 与枚举成员同名的原始值)

• 递归枚举

indirect enum ArithExper {
    case num(Int)
    case sum(ArithExper, ArithExper)
    case dif(ArithExper, ArithExper)
}

enum ArithExper1 {
    case num(Int)
    indirect case sum(ArithExper, ArithExper)
    indirect case dif(ArithExper, ArithExper)
}

let zore = ArithExper.num(0)
let two = ArithExper.num(2)
let sum = ArithExper.sum(zore, two)

func calculate(_ expr: ArithExper) -> Int {
    
    switch expr {
    case let .num(value):
        return value
    case let .sum(left, right):
        return calculate(left) + calculate(right)
    case let .dif(left, right):
        return calculate(left) - calculate(right)
    }
    
}

print(calculate(sum))

枚举变量内存布局

https://github.com/CoderMJLee/Mems 查看内存地址工具

小端:高高低低 内存地址高的放到高字节，内存地址低的放到低字节

1. 1个字节存储成员值
2. N个字节存储关联值（N取占用内存最大的关联值），任何一个case的关联值都共用这N个字节，默认值不占用枚举变量内存

enum TestEnum {
    case test1(Int, Int, Int)
    case test2(Int, Int)
    case test3(Int)
    case test4(Bool)
    case test5
}
 var e = TestEnum.test1(1, 2, 3)
// 01 00 00 00 00 00 00 00
// 02 00 00 00 00 00 00 00
// 03 00 00 00 00 00 00 00
// 00
// 00 00 00 00 00 00 00

e = .test4(true)
// 01 00 00 00 00 00 00 00
// 00 00 00 00 00 00 00 00
// 00 00 00 00 00 00 00 00
// 03
// 00 00 00 00 00 00 00