7. Closures, Extensions, Protocols, Delegation, and ScrollView - 笔记

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[weak self] 比[unowned self]更安全。

拓展：分割代码快，更简洁，不要滥用

协议：是一个更简洁表达API的方式。是一种类型： 协议用在属性/方法的参数或返回值中。

下面是协议的一个例子：

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protocol Moveable {
    mutating func moveTo(p: CGPoint)
}

class Car: Moveable {
    func moveTo(p: CGPoint) {
        print("Car move to \(p)")
    }

    func changeOil() {
        print("changeOil")
    }

    var name: String

    init() {
        self.name = ""
    }

    init(name: String) {
        self.name = name
    }

}

struct Shape: Moveable {
    mutating func moveTo(p: CGPoint) {
        print("Shape move to \(p)")
    }

    func draw() {

        print("draw")
    }
}

let prius: Car = Car(name: "A")
let square: Shape = Shape()

var thingToMove: Moveable = prius
thingToMove.moveTo(CGPoint(x: 100, y: 100))
var find: Car = prius
find.name

// 协议可以作为一个类型，来存储实现该协议的变量，但是不能直接调用后者的非协议的方法和属性
//thingToMove.changeOil()
thingToMove = square

let thingsToMove: [Moveable] = [prius, square]

func slide(var slider: Moveable) {
    let positionToSlideTo = CGPoint(x: 88, y: 88)
    slider.moveTo(positionToSlideTo)
}

slide(prius)
slide(square)

protocol Slippery {
    var speed: Double { get }
}

extension Car: Slippery {
    var speed: Double {
        return 1
    }
}

func slipAndSlide(x: protocol<Slippery, Moveable>) {
    print("slipAndSlide")
}
slipAndSlide(prius)