Swift开发基础04-枚举

基本用法

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

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

var dir = Direction.west
dir = Direction.east
dir = .north
print(dir) // north

switch dir {
case .north:
    print("north")
case .south:
    print("south")
case .east:
    print("east")
case .west:
    print("west")
}

关联值(Associated Values)

有时会将枚举的成员值跟其他类型的关联存储在一起,会非常有用

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

var score = Score.points(96)
score = .grade("A")

switch score {
case let .points(i):
    print(i, "points")
case let .grade(i):
    print("grade", i)
} // grade A

enum Date {
    case digit(year: Int, month: Int, day: Int)
    case string(String)
}
var date = Date.digit(year: 2011, month: 9, day: 10)
date = .string("2011-09-10")
switch date {
case .digit(let year, let month, let day):
    print(year, month, day)
case let .string(value):
    print(value)
}
//  必要时let也可以改为var

原始值(Raw Values)

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 PokerSuit : Character {
     case spade = ""
     case heart = ""
     case diamond = ""
     case club = ""
}

var suit = PokerSuit.spade
print(suit) // spade
print(suit.rawValue) //
print(PokerSuit.club.rawValue) //

enum Grade : String {
    case perfect = "A"
    case great = "B"
    case good = "C"
    case bad = "D"
}
print(Grade.perfect.rawValue) // A
print(Grade.great.rawValue) // B
print(Grade.good.rawValue) // C
print(Grade.bad.rawValue) // D

隐式原始值(Implicitly Assigned Raw Values)

如果枚举的原始值类型是Int、String，Swift会自动分配原始值

enum Direction : String {
    case north = "north"
    case south = "south"
    case east = "east"
    case west = "west"
}
// 等价于
enum Direction : String {
    case north, south, east, west
}
print(Direction.north) // north
print(Direction.north.rawValue) // north

enum Season : Int {
    case spring, summer, autumn, winter
}
print(Season.spring.rawValue) // 0
print(Season.summer.rawValue) // 1
print(Season.autumn.rawValue) // 2
print(Season.winter.rawValue) // 3
enum Season : Int {
    case spring = 1, summer, autumn = 4, winter
}
print(Season.spring.rawValue) // 1
print(Season.summer.rawValue) // 2
print(Season.autumn.rawValue) // 4
print(Season.winter.rawValue) // 5

递归枚举 (indirect)

indirect enum ArithExpr {
    case number(Int)
    case sum(ArithExpr, ArithExpr)
    case difference(ArithExpr, ArithExpr)
}

enum ArithExpr {
    case number(Int)
    indirect case sum(ArithExpr, ArithExpr) 
　　 indirect case difference(ArithExpr, ArithExpr)
}
let five = ArithExpr.number(5)
let four = ArithExpr.number(4)
let two = ArithExpr.number(2)
let sum = ArithExpr.sum(five, four)
let difference = ArithExpr.difference(sum, two)

func calculate(_ expr: ArithExpr) -> Int { switch expr {
case let .number(value):
    return value
case let .sum(left, right):
    return calculate(left) + calculate(right)
case let .difference(left, right):
    return calculate(left) - calculate(right)
    } }
calculate(difference)

MemoryLayout

可以使用MemoryLayout获取数据类型占用的内存大小

enum Password {
    case number(Int, Int, Int, Int)
    case other
}
MemoryLayout<Password>.stride // 40, 分配占用的空间大小
MemoryLayout<Password>.size // 33, 实际用到的空间大小
MemoryLayout<Password>.alignment // 8, 对齐参数

var pwd = Password.number(9, 8, 6, 4)
pwd = .other
MemoryLayout.stride(ofValue: pwd) // 40
MemoryLayout.size(ofValue: pwd) // 33
MemoryLayout.alignment(ofValue: pwd) // 8

窥探枚举的内存

1、枚举有2个case及以上的情况

enum TestEnum {
        case test1(Int, Int, Int)
        case test2(Int, Int)
        case test3(Int)
        case test4(Bool)
        case test5
    }

MemoryLayout<TestEnum>.stride       // 32, 分配占用的空间大小

MemoryLayout<TestEnum>.size         // 25, 实际用到的空间大小

MemoryLayout<TestEnum>.alignment // 8, 对齐参数

通过观察枚举变量e的内存布局：

test1

    // 1个字节存储成员值
    // 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
    // 共用体

    // 小端：高高低低
    // 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
    var e = TestEnum.test1(1, 2, 3)

test2

    // 04 00 00 00 00 00 00 00
    // 05 00 00 00 00 00 00 00
    // 00 00 00 00 00 00 00 00
    // 01
    // 00 00 00 00 00 00 00
    e = .test2(4, 5)

test3

    // 06 00 00 00 00 00 00 00
    // 00 00 00 00 00 00 00 00
    // 00 00 00 00 00 00 00 00
    // 02
    // 00 00 00 00 00 00 00
    e = .test3(6)

test4

    // 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
    e = .test4(true)

test5

    // 00 00 00 00 00 00 00 00
    // 00 00 00 00 00 00 00 00
    // 00 00 00 00 00 00 00 00
    // 04
    // 00 00 00 00 00 00 00
    e = .test5

2、枚举只有1个case的情况（其实一个case也多大意义了）

enum TestEnum {
    case test1(Int, Int, Int)
}

var e = TestEnum.test1(10, 20, 30)

MemoryLayout.stride(ofValue: e) // 24, 分配占用的空间大小
MemoryLayout.size(ofValue: e) // 24, 实际用到的空间大小
MemoryLayout.alignment(ofValue: e) // 8, 对齐参数

test1

// 0A 00 00 00 00 00 00 00
// 14 00 00 00 00 00 00 00
// 1E 00 00 00 00 00 00 00
var e = TestEnum.test1(10, 20, 30)

这种情况就不需要存储成员值了，直接开辟24个字节存关联值