Add new superclass_delegating_accessors. Similar to class inheritable attributes but with subtly different semantics. [Koz, tarmo]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8056 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

2 files changed, 41 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/class.rb b/activesupport/lib/active_support/core_ext/class.rb
index 83eb8135f4..44ad6c8c08 100644
--- a/activesupport/lib/active_support/core_ext/class.rb
+++ b/activesupport/lib/active_support/core_ext/class.rb
@@ -1,3 +1,4 @@
 require 'active_support/core_ext/class/attribute_accessors'
 require 'active_support/core_ext/class/inheritable_attributes'
 require 'active_support/core_ext/class/removal'
+require 'active_support/core_ext/class/delegating_attributes'
diff --git a/activesupport/lib/active_support/core_ext/class/delegating_attributes.rb b/activesupport/lib/active_support/core_ext/class/delegating_attributes.rb
new file mode 100644
index 0000000000..f5f0ef8779
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/class/delegating_attributes.rb
@@ -0,0 +1,40 @@
+# These class attributes behave something like the class
+# inheritable accessors.  But instead of copying the hash over at
+# the time the subclass is first defined,  the accessors simply
+# delegate to their superclass unless they have been given a 
+# specific value.  This stops the strange situation where values 
+# set after class definition don't get applied to subclasses.
+class Class
+  def superclass_delegating_reader(*names)
+    class_name_to_stop_searching_on = self.superclass.name.blank? ? "Object" : self.superclass.name
+    names.each do |name|
+      class_eval <<-EOS
+      def self.#{name}
+        if defined?(@#{name})
+          @#{name}
+        elsif superclass < #{class_name_to_stop_searching_on} && superclass.respond_to?(:#{name})
+          superclass.#{name}
+        end
+      end
+      def #{name}
+        self.class.#{name}
+      end
+      EOS
+    end
+  end
+
+  def superclass_delegating_writer(*names)
+    names.each do |name|
+      class_eval <<-EOS
+        def self.#{name}=(value)
+          @#{name} = value
+        end
+      EOS
+    end
+  end
+
+  def superclass_delegating_accessor(*names)
+    superclass_delegating_reader(*names)
+    superclass_delegating_writer(*names)
+  end
+end
\ No newline at end of file