1 files changed, 115 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/core_ext/class/inheritable_attributes.rb b/activesupport/lib/active_support/core_ext/class/inheritable_attributes.rb
new file mode 100644
index 0000000000..2e70a64436
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/class/inheritable_attributes.rb
@@ -0,0 +1,115 @@
+# Retain for backward compatibility.  Methods are now included in Class.
+module ClassInheritableAttributes # :nodoc:
+end
+
+# Allows attributes to be shared within an inheritance hierarchy, but where each descendant 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.
+class Class # :nodoc:
+  def class_inheritable_reader(*syms)
+    syms.each do |sym|
+      class_eval <<-EOS
+        def self.#{sym}
+          read_inheritable_attribute(:#{sym})
+        end
+
+        def #{sym}
+          self.class.#{sym}
+        end
+      EOS
+    end
+  end
+
+  def class_inheritable_writer(*syms)
+    syms.each do |sym|
+      class_eval <<-EOS
+        def self.#{sym}=(obj)
+          write_inheritable_attribute(:#{sym}, obj)
+        end
+
+        def #{sym}=(obj)
+          self.class.#{sym} = obj
+        end
+      EOS
+    end
+  end
+
+  def class_inheritable_array_writer(*syms)
+    syms.each do |sym|
+      class_eval <<-EOS
+        def self.#{sym}=(obj)
+          write_inheritable_array(:#{sym}, obj)
+        end
+
+        def #{sym}=(obj)
+          self.class.#{sym} = obj
+        end
+      EOS
+    end
+  end
+
+  def class_inheritable_hash_writer(*syms)
+    syms.each do |sym|
+      class_eval <<-EOS
+        def self.#{sym}=(obj)
+          write_inheritable_hash(:#{sym}, obj)
+        end
+
+        def #{sym}=(obj)
+          self.class.#{sym} = obj
+        end
+      EOS
+    end
+  end
+
+  def class_inheritable_accessor(*syms)
+    class_inheritable_reader(*syms)
+    class_inheritable_writer(*syms)
+  end
+
+  def class_inheritable_array(*syms)
+    class_inheritable_reader(*syms)
+    class_inheritable_array_writer(*syms)
+  end
+
+  def class_inheritable_hash(*syms)
+    class_inheritable_reader(*syms)
+    class_inheritable_hash_writer(*syms)
+  end
+
+  def inheritable_attributes
+    @inheritable_attributes ||= {}
+  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 write_inheritable_hash(key, hash)
+    write_inheritable_attribute(key, {}) if read_inheritable_attribute(key).nil?
+    write_inheritable_attribute(key, read_inheritable_attribute(key).merge(hash))
+  end
+
+  def read_inheritable_attribute(key)
+    inheritable_attributes[key]
+  end
+  
+  def reset_inheritable_attributes
+    inheritable_attributes.clear
+  end
+
+  private 
+    def inherited_with_inheritable_attributes(child)
+      inherited_without_inheritable_attributes(child) if respond_to?(:inherited_without_inheritable_attributes)
+      child.instance_variable_set('@inheritable_attributes', inheritable_attributes.dup)
+    end
+
+    alias inherited_without_inheritable_attributes inherited
+    alias inherited inherited_with_inheritable_attributes
+end