config.rb

module MyApp
  def config
    Config.instance
  end

  class Config
    include Singleton

    attr_reader :env

    def initialize
      yml = YAML.load_file("config.yml")
      @env = ENV.fetch('MY_APP_ENV', :development)
      @config = Hashie::Mash.new(yml[@env])
    end

    def method_missing(name, *args, &block)
      # if there is no method delegate to @config Mash.
    end
  end
end