Question

I am trying to understand how the following code is able to do this:

attr_accessor *Configuration::VALID_CONFIG_KEYS

Without requiring the Configuration file. Here is part of the code:

require 'openamplify/analysis/context'
require 'openamplify/connection'
require 'openamplify/request'

module OpenAmplify
  # Provides access to the OpenAmplify API http://portaltnx20.openamplify.com/AmplifyWeb_v20/
  #
  # Basic usage of the library is to call supported methods via the Client class.
  #
  #   text = "After getting the MX1000 laser mouse and the Z-5500 speakers i fell in love with logitech"
  #   OpenAmplify::Client.new.amplify(text)

  class Client
    include OpenAmplify::Connection
    include OpenAmplify::Request

    attr_accessor *Configuration::VALID_CONFIG_KEYS

    def initialize(options={})
      merged_options = OpenAmplify.options.merge(options)
      Configuration::VALID_CONFIG_KEYS.each do |key|
        send("#{key}=", merged_options[key])
      end
    end
  ....
  end

And this is the Configuration module:

require 'openamplify/version'

# TODO: output_format, analysis, scoring can be specied in the client and becomes the default unless overriden

module OpenAmplify
  # Defines constants and methods for configuring a client
  module Configuration
    VALID_CONNECTION_KEYS = [:endpoint, :user_agent, :method, :adapter].freeze
    VALID_OPTIONS_KEYS    = [:api_key, :analysis, :output_format, :scoring].freeze

    VALID_CONFIG_KEYS     = VALID_CONNECTION_KEYS + VALID_OPTIONS_KEYS

    DEFAULT_ENDPOINT      = 'http://portaltnx20.openamplify.com/AmplifyWeb_v21/AmplifyThis'
    DEFAULT_HTTP_METHOD   = :get
    DEFAULT_HTTP_ADAPTER  = :net_http
    DEFAULT_USER_AGENT    = "OpenAmplify Ruby Gem #{OpenAmplify::VERSION}".freeze

    DEFAULT_API_KEY       = nil
    DEFAULT_ANALYSIS      = :all
    DEFAULT_OUTPUT_FORMAT = :xml
    DEFAULT_SCORING       = :standard
    DEFAULT_SOURCE_URL    = nil
    DEFAULT_INPUT_TEXT    = nil

    attr_accessor *VALID_CONFIG_KEYS
  ....
 end

This is from this repository: OpenAmplify

Answer 1

First of all, in both configuration.rb and client.rb, they’re using the same naming space, which is module OpenAmplify.

Even though configuration.rb is not required in client.rb, the convention of Ruby project usually requires all necessary files in one file (normally the same name as the name space, and placed in {ProjectName}/lib/, in this case the file is openamplify/lib/openamplify.rb).

So if you go to openamplify/lib/openamplify.rb, you’ll notice it actually requires all those two files:

require 'openamplify/configuration'
require 'openamplify/client'

And since constants are already defined in configuration.rb:

module OpenAmplify
  module Configuration
    VALID_CONFIG_KEYS = ...
  end
end

Then obviously constant VALID_CONFIG_KEYS is visible in the same module (re-opened by client.rb) by Configuration::VALID_CONFIG_KEYS (and the * in front just means exploding array, because VALID_CONFIG_KEYS is an array of symbols)

module OpenAmplify
  class Client
    attr_accessor *Configuration::VALID_CONFIG_KEYS
  end
end