用隱式參數重載case類構造函數？

我想用一些具有默認值的參數來定義一個case類，但默認值需要一個隱式參數。我已經試過這樣的事情：用隱式參數重載case類構造函數？

case class ChannelLatches(started: TestLatch, stopped: TestLatch)(implicit system: ActorSystem) { 
    def this()(implicit system: ActorSystem) = this(new TestLatch(), new TestLatch())(system) 
}

這：

case class ChannelLatches(started: TestLatch, stopped: TestLatch)(implicit system: ActorSystem) { 
    def this()(implicit system: ActorSystem) = this(new TestLatch(), new TestLatch())(system) 
}

但在這兩種情況下，編譯器無法識別我的新的構造。任何指針？

來源

2012-03-04 jxstanford

案例類ChannelLatches（開始：TestLatch =新TestLatch，停止：TestLatch =新TestLatch）（隱含的系統：ActorSystem）{ } – Eastsun 2012-03-04 05:21:35

這是我試過的，可是編譯器會產生這樣的錯誤：找不到參數系統的隱式值：akka.actor.ActorSystem。我假設因爲系統是在後續的參數列表中定義的。 – jxstanford 2012-03-04 06:20:47

問題不在案例類或其構造函數中。當你得到像

scala> val channelLatches = new ChannelLatches 
<console>:11: error: could not find implicit value for parameter system: ActorSystem 
     val channelLatches = new ChannelLatches 
          ^

編譯錯誤，這意味着你不必型ActorSystem的可作爲範圍單一的標識符的隱含變量。

無論你的代碼示例（它們是完全相同的代碼，對吧？），並@東日的例子是完全合法的代碼：

scala> class ActorSystem 
defined class ActorSystem 

scala> class TestLatch 
defined class TestLatch 

scala> case class ChannelLatches(started: TestLatch = new TestLatch, stopped: TestLatch = new TestLatch)(implicit system: ActorSystem) 
defined class ChannelLatches 

scala> implicit val actor = new ActorSystem 
actor: ActorSystem = [email protected] 

scala> val channelLatches = new ChannelLatches 
channelLatches: ChannelLatches = ChannelLatches([email protected],[email protected])

注意隱含的VAL演員這使得編譯器供應隱含地缺少參數。

約隱含參數的介紹請參見A Tour of Scala: Implicit Parameters。

---編輯2012-03-05：新增的替代例子ChannelLatches是內部類的東西

如果你想ChannelLatches是一個內部類的東西，你真的不需要通過ActorSystem實例添加到內部類實例中，因爲內部類可以訪問外部對象的值。 A Tour of Scala: Inner Classes

scala> class ActorSystem 
defined class ActorSystem 

scala> class TestLatch 
defined class TestLatch 

scala> class Something(implicit val as: ActorSystem) { 
    | case class ChannelLatches(started: TestLatch, stopped: TestLatch) { 
    |  def this() = this(new TestLatch(), new TestLatch()) 
    | 
    |  def actorSystem = as 
    | } 
    | } 
defined class Something 

scala> implicit val as = new ActorSystem 
as: ActorSystem = [email protected] 

scala> val s = new Something 
s: Something = [email protected] 

scala> val cl = new s.ChannelLatches 
cl: s.ChannelLatches = ChannelLatches([email protected],[email protected]) 

scala> cl.actorSystem == as 
res0: Boolean = true

來源

2012-03-04 07:11:49 Lauri

我試圖找到一種方法來讓ChannelLatches不是某個隱式系統的內部類。這就是爲什麼我要定義case類的隱式參數（當然，這在這種情況下不起作用）。 ActorSystem需要由調用者提供。 – jxstanford 2012-03-04 23:14:07

用隱式參數重載case類構造函數？

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