protocol SomeEngine {
    func start()
}

// 전기차
class Electronic: SomeEngine {
    func start() {
        print("찌릿찌릿")
    }
}

// 모터차
class Gasoline: SomeEngine {
    func start() {
        print("부릉부릉")
    }
}

class Car {
    
    private let engine: SomeEngine
    
    init(engine: SomeEngine) {
        self.engine = engine
    }
    
    func start() {
        engine.start()
    }
    
}

let electronic = Electronic()
let gasoline = Gasoline()

let carA = Car(engine: electronic)
let carB = Car(engine: gasoline)

carA.start()
carB.start()