neopoly/nested_config

class NestedConfig
  # Evaluates a config value once replacing the original value
  # if the value responds to method +call+.
  #
  # == Example
  #
  #   class MyConfig < NestedConfig
  #     include NestedConfig::EvaluateOnce
  #   end
  #
  #   config = MyConfig.new
  #   config.startup_time = proc { Time.now }
  #   config.env = proc { |env| env.to_s.upcase }
  #
  #   config.startup_time # => 2012-06-05 15:57:36 +0200
  #   config.startup_time # => 2012-06-05 15:57:36 +0200
  #
  #   config.env(:development) # => DEVELOPMENT
  #   config.env               # => DEVELOPMENT
  module EvaluateOnce
    def [](key, *args)
      value = super
      if value.respond_to?(:call)
        self[key] = value.call(*args)
      else
        value
      end
    end
  end
end