无法访问伴随对象案例对象

Question

我正在使用scala 2.12，我尝试了一段在2.11版本中编码的代码，它不再编译了：

object MusicController {
    sealed trait ControllerMsg
    case object Play extends ControllerMsg
    case object Stop extends ControllerMsg
}

// Music Controller
class MusicController extends Actor {
    def receive = {
        case Play =>
            println("Music Started ...")
        case Stop =>
            println("Music Stopped ...")
    }
}

我有以下编译错误：

not found: value Play
[error]         case Play =>
not found: value Stop
[error]         case Stop =>

Answer 1

您需要导入MusicController的案例对象

object MusicController {
    sealed trait ControllerMsg
    case object Play extends ControllerMsg
    case object Stop extends ControllerMsg
}

// Music Controller
class MusicController extends Actor {
    import MusicController._ // <-- IMPORT THIS
    def receive = {
        case Play =>
            println("Music Started ...")
        case Stop =>
            println("Music Stopped ...")
    }
}