Minor code restructuring for SubchannelClassification

akka-actor/src/main/scala/akka/event/EventBus.scala

@@ -137,25 +137,18 @@ trait SubchannelClassification { this: EventBus ⇒
 
   def subscribe(subscriber: Subscriber, to: Classifier): Boolean = subscriptions.synchronized {
     val diff = subscriptions.addValue(to, subscriber)
-    if (diff.isEmpty) false
-    else {
-      addToCache(diff)
-      true
-    }
+    addToCache(diff)
+    diff.nonEmpty
   }
 
   def unsubscribe(subscriber: Subscriber, from: Classifier): Boolean = subscriptions.synchronized {
     val diff = subscriptions.removeValue(from, subscriber)
-    if (diff.isEmpty) false
-    else {
-      cache ++= diff
-      true
-    }
+    cache ++= diff // FIXME What is the reason this isn't calling removeFromCache?
+    diff.nonEmpty
   }
 
   def unsubscribe(subscriber: Subscriber): Unit = subscriptions.synchronized {
-    val diff = subscriptions.removeValue(subscriber)
-    if (diff.nonEmpty) removeFromCache(diff)
+    removeFromCache(subscriptions.removeValue(subscriber))
   }
 
   def publish(event: Event): Unit = {
@@ -174,12 +167,8 @@ trait SubchannelClassification { this: EventBus ⇒
 
   // we can only let keys that already exist in the cache get updated
   private def removeFromCache(changes: Seq[(Classifier, Set[Subscriber])]): Unit =
-    cache ++= (List.empty[(Classifier, Set[Subscriber])] /: changes) {
-      case (cl, (c, cs)) ⇒
-        cache.get(c) match {
-          case None     ⇒ cl
-          case Some(ss) ⇒ (c, ss -- cs) :: cl
-        }
+    cache = (cache /: changes) {
+      case (m, (c, cs)) ⇒ m.updated(c, m.getOrElse(c, Set.empty[Subscriber]) -- cs)
     }
 
   private def addToCache(changes: Seq[(Classifier, Set[Subscriber])]): Unit =