1 files changed, 14 insertions, 8 deletions
diff --git a/activemodel/lib/active_model/observing.rb b/activemodel/lib/active_model/observing.rb
index 32f2aa46bd..35b1a1f0c7 100644
--- a/activemodel/lib/active_model/observing.rb
+++ b/activemodel/lib/active_model/observing.rb
@@ -4,6 +4,8 @@ require 'active_support/core_ext/module/aliasing'
 require 'active_support/core_ext/module/remove_method'
 require 'active_support/core_ext/string/inflections'
 require 'active_support/core_ext/enumerable'
+require 'active_support/deprecation'
+require 'active_support/core_ext/object/try'
 require 'active_support/descendants_tracker'
 
 module ActiveModel
@@ -69,15 +71,21 @@ module ActiveModel
       end
 
       # Notify list of observers of a change.
-      def notify_observers(*arg)
-        observer_instances.each { |observer| observer.update(*arg) }
+      def notify_observers(*args)
+        observer_instances.each { |observer| observer.update(*args) }
       end
 
       # Total number of observers.
-      def count_observers
+      def observers_count
         observer_instances.size
       end
 
+      def count_observers
+        msg = "count_observers is deprecated in favor of observers_count"
+        ActiveSupport::Deprecation.warn(msg)
+        observers_count
+      end
+
       protected
         def instantiate_observer(observer) #:nodoc:
           # string/symbol
@@ -205,15 +213,12 @@ module ActiveModel
       # The class observed by default is inferred from the observer's class name:
       #   assert_equal Person, PersonObserver.observed_class
       def observed_class
-        if observed_class_name = name[/(.*)Observer/, 1]
-          observed_class_name.constantize
-        else
-          nil
-        end
+        name[/(.*)Observer/, 1].try :constantize
       end
     end
 
     # Start observing the declared classes and their subclasses.
+    # Called automatically by the instance method.
     def initialize
       observed_classes.each { |klass| add_observer!(klass) }
     end
@@ -242,6 +247,7 @@ module ActiveModel
         klass.add_observer(self)
       end
 
+      # Returns true if notifications are disabled for this object.
       def disabled_for?(object)
         klass = object.class
         return false unless klass.respond_to?(:observers)