vendor/rails/activesupport/lib/active_support/core_ext/class/delegating_attributes.rb

   1 # These class attributes behave something like the class
   2 # inheritable accessors.  But instead of copying the hash over at
   3 # the time the subclass is first defined,  the accessors simply
   4 # delegate to their superclass unless they have been given a
   5 # specific value.  This stops the strange situation where values
   6 # set after class definition don't get applied to subclasses.
   7 class Class
   8   def superclass_delegating_reader(*names)
   9     class_name_to_stop_searching_on = self.superclass.name.blank? ? "Object" : self.superclass.name
  10     names.each do |name|
  11       class_eval <<-EOS
  12       def self.#{name}                                            # def self.only_reader
  13         if defined?(@#{name})                                     #   if defined?(@only_reader)
  14           @#{name}                                                #     @only_reader
  15         elsif superclass < #{class_name_to_stop_searching_on} &&  #   elsif superclass < Object &&
  16               superclass.respond_to?(:#{name})                    #         superclass.respond_to?(:only_reader)
  17           superclass.#{name}                                      #     superclass.only_reader
  18         end                                                       #   end
  19       end                                                         # end
  20       def #{name}                                                 # def only_reader
  21         self.class.#{name}                                        #   self.class.only_reader
  22       end                                                         # end
  23       def self.#{name}?                                           # def self.only_reader?
  24         !!#{name}                                                 #   !!only_reader
  25       end                                                         # end
  26       def #{name}?                                                # def only_reader?
  27         !!#{name}                                                 #   !!only_reader
  28       end                                                         # end
  29       EOS
  30     end
  31   end
  32
  33   def superclass_delegating_writer(*names)
  34     names.each do |name|
  35       class_eval <<-EOS
  36         def self.#{name}=(value)  # def self.only_writer=(value)
  37           @#{name} = value        #   @only_writer = value
  38         end                       # end
  39       EOS
  40     end
  41   end
  42
  43   def superclass_delegating_accessor(*names)
  44     superclass_delegating_reader(*names)
  45     superclass_delegating_writer(*names)
  46   end
  47 end