Rails AppConfig inplementation for application configuration

app_config.rb

class AppConfig
  instance_methods.each { |m| undef_method m unless m =~ /^__|is_a\?|empty?/ }
  
  def initialize
    @hash = Hash.new do |hash, key|
      hash[key] = AppConfig.new unless @finalized
    end
  end
  
  def method_missing(message, value = nil)
    if message.to_s !~ /=$/
      @hash[message]
    else
      raise ArgumentError, 'Configuration has been finalized' if @finalized
      @hash.store(message.to_s.gsub(/=$/, '').to_sym, value)
    end
  end
  
  def finalize
    @finalized = true
    @hash.each do |key, value|
      if value.is_a?(AppConfig)
        if value.empty?
          @hash.delete(key)
        else
          value.finalize
        end
      end 
    end
  end
  
  def empty?
    @hash.empty?
  end
  
  def inspect
    @hash.inspect
  end
  
  module Shortcut
    def app_config
      Rails.configuration.app
    end
  end
end

class Rails::Configuration
  def app
    @app ||= begin
      after_initialize do
        @app.finalize
        ['::ActiveRecord::Base', '::ActionController::Base', '::ActionView::Base', 
         '::ActionMailer::Base', '::ActionController::TestCase'].each do |klass_name|
          klass = klass_name.constantize
          klass.__send__(:include, AppConfig::Shortcut)
          klass.extend(AppConfig::Shortcut)
        end
      end
      AppConfig.new
    end
  end
end