example1

final class Car {

    enum Direction: CustomStringConvertible {
        case straight
        case right
        var description: String {
            switch self {
            case .right:
                return "right"
            case .straight:
                return "straight"
            }
        }
    }

    func go(direction: Direction) {
        print(direction.description)
    }
}

protocol Drivable: class {
    func drive()
}

final class A: Drivable {

    private let car = Car.init()

    func drive() {
        car.go(direction: .straight)
    }
}

final class B: Drivable {

    private let car = Car.init()

    func drive() {
        car.go(direction: .right)
    }
}
let ad = A.init()
ad.drive()
let bd = B.init()
bd.drive()