原文

https://www.raywenderlich.com/148448/introducing-protocol-oriented-programming

Playground 笔记

protocol Bird: CustomStringConvertible{
    var name: String { get }
}

protocol Flyable{
    var airspeedVelocity: Double { get }
}

extension CustomStringConvertible where Self: Bird {
    var description: String {
        return canFly ? "I can fly" : "Guess I’ll just sit here :["
    }
}

extension Bird{
    var canFly: Bool {
        return self is Flyable
    }
}

struct FlappyBird: Bird, Flyable{
    var airspeedVelocity: Double{
        return 3 * flappyAmplitude * flappyFrequency
    }

    let flappyAmplitude: Double
    let flappyFrequency: Double

    let name: String
}

struct Penguin: Bird{
    let name: String
}

struct SwiftBird: Bird, Flyable{
    var name: String { return "Swfit \(version)" }
    let version: Double
    
    var airspeedVelocity: Double{
        return version * 1000
    }
}

enum UnladenSwallow: Bird, Flyable{
    case african
    case european
    case unknown
    
    var name: String{
        switch self {
        case .african:
            return "African"
        case .european:
            return "European"
        default:
            return "Unknown"
        }
    }
    
    var airspeedVelocity: Double{
        switch self {
        case .african:
            return 10
        case .european:
            return 9
        default:
            return 0
        }
    }
}

extension UnladenSwallow{
    var canFly: Bool{
        return self != .unknown
    }
}

UnladenSwallow.african

let numbers = [10, 20, 30, 40, 50]
let slice = numbers[1...3]
let reversedSlice = slice.reversed()

let answer = reversedSlice.map { $0 * 10 }


class Motorcycle{
    var name: String
    var speed: Double
    
    init(name: String) {
        self.name = name
        speed = 200
    }
}

protocol Racer{
    var speed: Double { get }
}

extension FlappyBird: Racer{
    var speed: Double{
        return airspeedVelocity
    }
}

extension SwiftBird: Racer{
    var speed: Double{
        return airspeedVelocity
    }
}

extension Penguin: Racer{
    var speed: Double{
        return 42
    }
}

extension UnladenSwallow: Racer{
    var speed: Double{
        return canFly ? airspeedVelocity : 0 
    }
}

extension Motorcycle: Racer {}

let racers: [Racer] = [
    UnladenSwallow.african,
    UnladenSwallow.european,
    UnladenSwallow.unknown,
    FlappyBird(flappyAmplitude: 3, flappyFrequency: 20, name: "Flappy Bird"),
    SwiftBird(version: 3.0),
    Penguin(name: "King Penguin"),
    Motorcycle(name: "BMW Motorcycle")
]



extension Sequence where Iterator.Element == Racer{
    func topSpeed() -> Double{
        return self.max(by: { $0.speed < $1.speed })?.speed ?? 0
    }
}

racers[1...3].topSpeed()


protocol Score: Equatable, Comparable{
    var value: Int { get }
}

struct RacingScore: Score{
    let value: Int
    
    static func ==(lhs: RacingScore, rhs: RacingScore) -> Bool{
        return lhs.value == rhs.value
    }
    
    static func <(lhs: RacingScore, rhs: RacingScore) -> Bool{
        return lhs.value < rhs.value
    }
}

RacingScore(value: 120) > RacingScore(value: 100)