rails--rails/activesupport/lib/active_support/configurable.rb

require 'active_support/concern'
require 'active_support/ordered_options'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/module/delegation'

module ActiveSupport
  module Configurable
    extend ActiveSupport::Concern

    module ClassMethods
      def config
        @config ||= ActiveSupport::InheritableOptions.new(superclass.respond_to?(:config) ? superclass.config : {})
      end

      def configure
        yield config
      end

      def config_accessor(*names)
        names.each do |name|
          code, line = <<-RUBY, __LINE__ + 1
            def #{name}; config.#{name}; end
            def #{name}=(value); config.#{name} = value; end
          RUBY

          singleton_class.class_eval code, __FILE__, line
          class_eval code, __FILE__, line
        end
      end
    end

    def config
      @config ||= ActiveSupport::InheritableOptions.new(self.class.config)
    end
  end
end