枚举的基本用法

• 定义：枚举简单的说也是一种数据类型，只不过是这种数据类型只包含自定义的特定数据，它是一组有共同特性的数据的集合。

enum Direction {case northcase southcase eastcase west
}enum Direction {case north,south,east,west
}var dir = Direction.west
dir = Direction.east
dir = .north
print(dir) // northswitch dir {
case .north:print("north")
case .south:print("south")
case.east:print("east")
case .west:print("west")
}

关联值（Associated Values）

• 有时将枚举的成员值跟其他类型的值关联存储在一起，会非常有用

enum Score {case points(Int)case grade(Character)
}var score = Score.points(96)
score = 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: 2022, month: 10, day: 14)
date = .string("2022-10-14")
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

enum Password {case number(Int, Int, Int, Int)case gesture(String)
}var pwd = Password.number(3, 5, 7, 8)
pwd = .gesture("123456")switch pwd {
case let .number(n1, n2, n3, n4):print("number is", n1, n2, n3, n4)
case let .gesture(str):print("gesture is", str)
}

原始值（Raw Values）

• 枚举成员可以使用相同类型的默认值预先对应，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)
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

注意：原始值不占用枚举变量的内存

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 = "ease"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) //3enum 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（Recursive Enumeration）

递归枚举必须前面添加 indirect

indirect enum ArithExpr {case number(Int)case sum(ArithExpr, ArithExpr)case difference(ArithExpr, ArithExpr)
}
//或者
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 valuecase 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.stride // 40, 分配占用的空间大小
MemoryLayout.size // 33, 时机用到的空间大小
MemoryLayout.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