protocol PrintName{
    func PrintName()
}

class iPhone: PrintName {
    func PrintName() {
        print("it`s iPone")
    }
}

class iPad: PrintName {
    func PrintName() {
        print("it`s iPad") //所有子类的共同特性，要执行的方法
    }
}

enum DeviceType{
    case iPhone, iPad;
}

class MyDevice {
    static func printDeviceType(device: DeviceType) -> PrintName {
        switch device {
        case .iPhone:
            return iPhone()
        default:
            return iPad()
        }
    }
}

let myDevice = MyDevice.printDeviceType(device: .iPhone)
myDevice.PrintName() ///it`s iPone