protocol Drawable {
    func draw()
    var x: Int { get set }
    var y: Int { get }
    subscript(index: Int) -> Int { get set }
}

class Person: Drawable {
    var x: Int = 0
    let y: Int = 0
    func draw() {
        print("Person draw")
    }
    subscript(index: Int) -> Int {
        set {}
        get { index }
    }
}

class Person: Drawable {
    var x: Int {
        get { 0 }
        set {}
    }
    var y: Int {
        get { 0 }
    }
    func draw() {
        print("Person draw")
    }
    subscript(index: Int) -> Int {
        set {}
        get { index }
    }
}

protocol Drawable {
    static func draw()
}
class Person1: Drawable {
    class func draw() {
        print("Person1 draw")
    }
}
class Person2: Drawable {
    static func draw() {
        print("Person2 draw")
    }
}

protocol Drawable {
    mutating func draw()
}
class Size: Drawable {
    var width: Int = 0
    func draw() {
        width = 10
    }
}
static Point: Drawable {
    var x: Int = 0
    mutating func draw() {
        x = 10
    }
}

protocol Drawable {
    init(x: Int, y: Int)
}
class Point: Drawable {
    required init(x: Int, y: Int) {
        
    }
}
final class Size: Drawable {
    init(x: Int, y: Int) {
        
    }
}

protocol Liveable {
    init(age: Int)
}
class Person {
    init(age: Int) {}
}
class Student: Person, Liveable {
    required override init(age: Int) {
        super.init(age: age)
    }
}

protocol Liveable {
    init()
    init?(age: Int)
    init!(no: Int)
}
class Person: Liveable {
    required init() {}
//    required init!() {}
    required init?(age: Int) {}
//    required init!(age: Int) {}
//    required init(age: Int) {}
    required init!(no: Int) {}
//    required init?(no: Int) {}
//    required init(no: Int) {}
}

protocol Livable {}
protocol Runnable {}
class Person {}
//接收Person或者其子類的實(shí)例
func fn0(obj: Person) {}
//接收遵守Livable協(xié)議的實(shí)例
func fn1(obj: Livable) {}
//接收同時(shí)遵守Livable和Runnable協(xié)議的實(shí)例
func fn2(obj: Livable & Runnable) {}
//接收同時(shí)遵守Livable、Runnable協(xié)議，并且是Person或者其子類的實(shí)例
func fn3(obj: Person & Livable & Runnable) {}

typealias RealPerson = Person & Livable & Runnable
func fn4(obj: RealPerson) {}

enum Season: CaseIterable {
    case spring, summer, autumn, winter
}
let seasons = Season.allCases
print(seasons.count) // 4
for season in seasons {
    print(season)
}

class Person: CustomStringConvertible {
    var age: Int
    var name: String
    init(age: Int, name: String) {
        self.age = age
        self.name = name
    }
    var description: String {
        "age = \(age), name = \(name)"
    }
}
var p = Person(age: 10, name: "Jack")
print(p) // age = 10, name = Jack