path: root/activesupport/lib/active_support/core_ext/class/delegating_attributes.rb

require 'active_support/core_ext/object/blank'

class Class
  def superclass_delegating_reader(*names)
    class_name_to_stop_searching_on = superclass.name.blank? ? "Object" : superclass.name
    names.each do |name|
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def self.#{name}                                            # def self.only_reader
          if defined?(@#{name})                                     #   if defined?(@only_reader)
            @#{name}                                                #     @only_reader
          elsif superclass < #{class_name_to_stop_searching_on} &&  #   elsif superclass < Object &&
                superclass.respond_to?(:#{name})                    #         superclass.respond_to?(:only_reader)
            superclass.#{name}                                      #     superclass.only_reader
          end                                                       #   end
        end                                                         # end
        def #{name}                                                 # def only_reader
          self.class.#{name}                                        #   self.class.only_reader
        end                                                         # end
        def self.#{name}?                                           # def self.only_reader?
          !!#{name}                                                 #   !!only_reader
        end                                                         # end
        def #{name}?                                                # def only_reader?
          !!#{name}                                                 #   !!only_reader
        end                                                         # end
      EOS
    end
  end

  def superclass_delegating_writer(*names)
    names.each do |name|
      class_eval(<<-EOS, __FILE__, __LINE__ + 1)
        def self.#{name}=(value)     # def self.property=(value)
          @#{name} = value           #   @property = value
        end                          # end
      EOS
    end
  end

  # 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.
  def superclass_delegating_accessor(*names)
    superclass_delegating_reader(*names)
    superclass_delegating_writer(*names)
  end
end