Scala ObservableSet Trait示例用法

Question

有没有人可以帮忙告诉我如何使用Scala的ObservableSet特征（trait）？

非常感谢您的帮助。

- barroco

Answer 1

ObservableSet是一个扩展自Publisher特质的集合类型，它提供了基本的发布-订阅行为。一个简单的使用示例如下：

scala> class Counter(var count: Int) extends Publisher[String] {
          def inc(): Unit = {
              count += 1
              super.publish("updated count to: " + count)
          }
     }

scala> class S[Evt, Pub] extends Subscriber[Evt, Pub] {
         def notify(pub: Pub, event: Evt): Unit = println("got event: " + event)
      }
defined class S

scala> val s = new S[String, Counter#Pub]     
s: S[String,Counter#Pub] = S@7c27a30c

scala> val c = new Counter(1)
c: Counter = Counter@44ba70c

scala> c.subscribe(s)

scala> c.inc
got event: updated count to: 2

ObservableSet做的事情类似，当使用+=或+-方法添加或删除元素时，它会调用publish方法，参见以下示例（其中类S定义如上）：

scala> class MySet extends HashSet[Int] with ObservableSet[Int] {       
     override def +=(elem: Int): this.type = super.+=(elem);
     override def -=(elem: Int): this.type = super.-=(elem);
     override def clear: Unit = super.clear;      
}

defined class MySet

scala> val set = new MySet
set: MySet = Set()

scala> val subS = new S[Any, Any]
subCol: S[Any,Any] = S@3e898802

scala> set.subscribe(subS)

scala> set += 1
got event: Include(NoLo,1)
res: set.type = Set(1)

我一直懒得用任何类型定义S，但我无法立即正确地进行类型设置，并且没有花费太长时间来解决它。

- Arjan Blokzijl

---

不错的例子。不过第一个缺少“val c = Counter(0)”这一行代码。 - Brian

Answer 2

这些打字信息有点让人不舒服，但这是我使它工作的方法。欢迎提出简化打字的建议。包括类型别名在内的各种编辑：

import collection.mutable._
import collection.script._

val set = new HashSet[String] with ObservableSet[String] { }

type Msg = Message[String] with Undoable
type Sub = Subscriber[Msg, ObservableSet[String]]

val sub = new Sub() {
  def notify(pub: ObservableSet[String], event: Msg): Unit = {
    println("%s sent %s".format(pub, event))
    event match {
      case r:Remove[_] => println("undo!"); event.undo()
      case _ => 
    }
  }
}

set.subscribe(sub)

set += "foo"
set += "bar"
set -= "bar"

这将打印：

Set(foo) sent Include(NoLo,foo)
Set(bar, foo) sent Include(NoLo,bar)
Set(foo) sent Remove(NoLo,bar)
undo!
Set(bar, foo) sent Include(NoLo,bar)

有趣的是，撤销操作导致另一条消息被发布...

- huynhjl