• 枚举 结构体 类都可以定义实例方法,类型方法
• 实例方法(Instance Method):通过实例对象调用
• 类型方法 (Type Method):通过类型调用,用static或者class关键字定义

self

• 在实例方法中代表实例对象
• 在类型方法中代表类型
• 在类型方法static func getCount中,count等价于self.count Car.self.count Car.count

class Car {
    static var count = 0
    init() {
        Car.count += 1
    }
    static func getCount() -> Int { count }//省略return
}
let c0 = Car()
let c1 = Car()
let c2 = Car()

print(Car.getCount())//3
print(Car.self.getCount())

mutating

• 结构体和枚举是值类型,默认情况下,值类型的属性不能被自身的实例方法修改
• 在func关键字前加mutating可以允许这种修改行为

struct Point {
    var x = 0.0 , y = 0.0
    mutating func moveBy(deltaX:  Double, deltaY: Double) {
        x += deltaX
        y += deltaY
        //self = Point(x: x + deltaX, y: y + deltaY)
    }
}

enum StateSwitch {
    case low, middle ,high
    mutating func next() {
        switch self {
        case .low:
            self = .middle
        case .middle:
            self = .high
        case .high:
            self = .low
        }
    }
}

@discardableResult

• 在func前面加个@discardableResult,可以消除:函数调用后返回值未被使用的警告

struct Point {
    var x = 0.0 , y = 0.0
    
    mutating func moveX(deltaX:  Double) -> Double {
        x += deltaX
        return x
        //self = Point(x: x + deltaX, y: y + deltaY)
    }
}
var p = Point()
//警告:Result of call to 'moveX(deltaX:)' is unused
p.moveX(deltaX: 10)


struct Point {
    var x = 0.0 , y = 0.0
    @discardableResult mutating
     func moveX(deltaX:  Double) -> Double {
        x += deltaX
        return x
        //self = Point(x: x + deltaX, y: y + deltaY)
    }
}
var p = Point()
//使用@discardableResult修饰方法后课消除警告
p.moveX(deltaX: 10)

func get() -> Int {
    return 10
}
//Result of call to 'get()' is unused
get()

@discardableResult
func get() -> Int {
    return 10
}
//无警告
get()