From 1de61b2b1cb28ea09add8b8b935b5fb85035ae89 Mon Sep 17 00:00:00 2001
From: Nikita Gazarov <nikita@raquo.com>
Date: Wed, 17 Nov 2021 15:13:46 -0800
Subject: [PATCH] Misc: Make base onAddedExternalObserver method abstract

---
 src/main/scala/com/raquo/airstream/core/BaseObservable.scala | 2 +-
 src/main/scala/com/raquo/airstream/core/EventStream.scala    | 5 ++++-
 src/main/scala/com/raquo/airstream/core/Signal.scala         | 1 -
 3 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/main/scala/com/raquo/airstream/core/BaseObservable.scala b/src/main/scala/com/raquo/airstream/core/BaseObservable.scala
index e7126f14..0ffffd18 100644
--- a/src/main/scala/com/raquo/airstream/core/BaseObservable.scala
+++ b/src/main/scala/com/raquo/airstream/core/BaseObservable.scala
@@ -151,7 +151,7 @@ trait BaseObservable[+Self[+_] <: Observable[_], +A] extends Source[A] with Name
 
   protected[this] def addExternalObserver(observer: Observer[A], owner: Owner): Subscription
 
-  protected[this] def onAddedExternalObserver(@unused observer: Observer[A]): Unit = ()
+  protected[this] def onAddedExternalObserver(@unused observer: Observer[A]): Unit
 
   /** Child observable should call this method on its parents when it is started.
     * This observable calls [[onStart]] if this action has given it its first observer (internal or external).
diff --git a/src/main/scala/com/raquo/airstream/core/EventStream.scala b/src/main/scala/com/raquo/airstream/core/EventStream.scala
index 82a0f642..1e6c73db 100644
--- a/src/main/scala/com/raquo/airstream/core/EventStream.scala
+++ b/src/main/scala/com/raquo/airstream/core/EventStream.scala
@@ -9,7 +9,7 @@ import com.raquo.airstream.debug.{DebuggableEventStream, Debugger, DebuggerEvent
 import com.raquo.airstream.distinct.DistinctEventStream
 import com.raquo.airstream.eventbus.EventBus
 import com.raquo.airstream.misc.generated._
-import com.raquo.airstream.misc.{CollectEventStream, DropEventStream, FilterEventStream, FoldLeftSignal, MapEventStream, SignalFromEventStream}
+import com.raquo.airstream.misc.{CollectEventStream, FilterEventStream, FoldLeftSignal, MapEventStream, SignalFromEventStream}
 import com.raquo.airstream.split.{SplittableEventStream, SplittableOneEventStream}
 import com.raquo.airstream.timing.{FutureEventStream, _}
 
@@ -130,6 +130,9 @@ trait EventStream[+A] extends Observable[A] with BaseObservable[EventStream, A]
     new DebuggerEventStream[A](this, debugger)
   }
 
+  /** This is used in Signal-s. It's a no-op for Streams. */
+  override protected def onAddedExternalObserver(observer: Observer[A]): Unit = ()
+
   override def toObservable: EventStream[A] = this
 
 }
diff --git a/src/main/scala/com/raquo/airstream/core/Signal.scala b/src/main/scala/com/raquo/airstream/core/Signal.scala
index fba98414..b0cc37c3 100644
--- a/src/main/scala/com/raquo/airstream/core/Signal.scala
+++ b/src/main/scala/com/raquo/airstream/core/Signal.scala
@@ -134,7 +134,6 @@ trait Signal[+A] extends Observable[A] with BaseObservable[Signal, A] with Signa
 
   // @TODO[API] Use pattern match instead when isInstanceOf performance is fixed: https://github.com/scala-js/scala-js/issues/3815
   override protected def onAddedExternalObserver(observer: Observer[A]): Unit = {
-    super.onAddedExternalObserver(observer)
     observer.onTry(tryNow()) // send current value immediately
   }