1 files changed, 40 insertions, 0 deletions
diff --git a/lib/observer.rb b/lib/observer.rb
new file mode 100644
index 0000000000..9a753939a2
--- /dev/null
+++ b/lib/observer.rb
@@ -0,0 +1,40 @@
+# Observable Mixin
+# 
+# Observers must respond to update
+
+module Observable
+  def add_observer(observer)
+    @observer_peers = [] unless @observer_peers
+    unless defined? observer.update
+      raise NameError, "observer needs to respond to `update'" 
+    end
+    @observer_peers.push observer
+  end
+  def delete_observer(observer)
+    @observer_peers.delete observer if @observer_peers
+  end
+  def delete_observers
+    @observer_peers.clear if @observer_peers
+  end
+  def count_observers
+    if @observer_peers
+      @observer_peers.size
+    else
+      0
+    end
+  end
+  def changed(state=TRUE)
+    @observer_state = state
+  end
+  def changed?
+    @observer_state
+  end
+  def notify_observers(*arg)
+    if @observer_state
+      for i in @observer_peers
+	i.update(*arg)
+      end
+      @observer_state = FALSE
+    end
+  end
+end