1 files changed, 19 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/module/inclusion.rb b/activesupport/lib/active_support/core_ext/module/inclusion.rb
index efc00d6f28..4f23841645 100644
--- a/activesupport/lib/active_support/core_ext/module/inclusion.rb
+++ b/activesupport/lib/active_support/core_ext/module/inclusion.rb
@@ -1,4 +1,23 @@
 class Module
+  # Returns the classes in the current ObjectSpace where this module has been
+  # mixed in according to Module#included_modules.
+  #
+  #   module M
+  #   end
+  #   
+  #   module N
+  #     include M
+  #   end
+  #   
+  #   class C
+  #     include M
+  #   end
+  #   
+  #   class D < C
+  #   end
+  #
+  #   p M.included_in_classes # => [C, D]
+  #
   def included_in_classes
     classes = []
     ObjectSpace.each_object(Class) { |k| classes << k if k.included_modules.include?(self) }