1 files changed, 37 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/support/class_inheritable_attributes.rb b/activerecord/lib/active_record/support/class_inheritable_attributes.rb
new file mode 100644
index 0000000000..ee69646da0
--- /dev/null
+++ b/activerecord/lib/active_record/support/class_inheritable_attributes.rb
@@ -0,0 +1,37 @@
+# Allows attributes to be shared within an inheritance hierarchy, but where each descentent gets a copy of
+# their parents' attributes, instead of just a pointer to the same. This means that the child can add elements
+# to, for example, an array without those additions being shared with either their parent, siblings, or
+# children, which is unlike the regular class-level attributes that are shared across the entire hierarchy.
+module ClassInheritableAttributes # :nodoc:
+  def self.append_features(base)
+    super
+    base.extend(ClassMethods)
+  end
+  
+  module ClassMethods # :nodoc:
+    @@classes ||= {}
+    
+    def inheritable_attributes
+      @@classes[self] ||= {}
+    end
+    
+    def write_inheritable_attribute(key, value)
+      inheritable_attributes[key] = value
+    end
+    
+    def write_inheritable_array(key, elements)
+      write_inheritable_attribute(key, []) if read_inheritable_attribute(key).nil?
+      write_inheritable_attribute(key, read_inheritable_attribute(key) + elements)
+    end
+
+    def read_inheritable_attribute(key)
+      inheritable_attributes[key]
+    end
+    
+    private 
+      def inherited(child)
+        @@classes[child] = inheritable_attributes.dup
+      end
+      
+  end
+end