伴侶對象的情況下對象

Question

我使用Scala的2.12，我試了一段代碼，在2.11版本編碼的，它不會再編譯：

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 ...") 
    } 
} 

我有以下的編譯器錯誤：

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

Answer 1

您需要導入MusicController的對象來說

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 ...") 
    } 
}