在Scala中重载泛型事件处理程序

如果我定义以下通用事件处理程序

trait Handles[E <: Event] {
  def handle(event: E)
}

然后，如何创建一个类来实现这些事件的事件处理程序？。我试过：

class InventoryListView extends Handles[InventoryItemCreated] with Handles[InventoryItemDeactivated] {
    def handle(event: InventoryItemCreated) = {

    }

    def handle(event: InventoryItemDeactivated) = {

    }
  }

但Scala抱怨说，一个特征不能被遗传两次

---

我发现这暗示了一个解决方案，但它需要多个类（每个处理程序一个）。这真的是唯一的方法吗？或者是否有其他Scala构造可以用来使单个类实现多个通用事件处理程序（即使用case类、清单或其他奇特的构造）

我不知道如何在一个类中实现这一点（除了将

事件

设置为ADT并定义句柄以接受

事件

类型的参数。但这将消除您似乎正在寻找的类型安全性）

我建议改用类型类模式

trait Handles[-A, -E <: Event] {
  def handle(a: A, event: E)
}

trait Event {
  ...
}
class InventoryItemDeactivation(val id: UUID) extends Event
class InventoryItemCreation(val id: UUID, val name: String) extends Event

class InventoryListView {
  ...
}

implicit object InventoryListViewHandlesItemCreation extends 
    Handles[InventoryListView, InventoryItemCreation] = {
  def handle(v: InventoryListView, e: InventoryItemCreation) = {
    ...
  }
}

implicit object InventoryListViewHandlesItemDeactivation extends 
    Handles[InventoryListView, InventoryItemDeactivation] = {
  def handle(v: InventoryListView, e: InventoryItemDeactivation) = {
    ...
  }
}

def someMethod[A, E <: Event](a: A, e: E)
              (implicit ev: InventoryListView Handles InventoryItemCreation) = {
  ev.handle(a, e)
  ...
}

---

trait Handles[-A，-E两种独立的
handle
方法的优点是什么

def handle(rawEvent: Event) = rawEvent match {
  case e: InventoryItemCreated => ...
  case e: InventoryItemDeactivated => ...
}

def handle(rawEvent: Event) = rawEvent match {
  case e: InventoryItemCreated => ...
  case e: InventoryItemDeactivated => ...
}