figgy

Provides convenient access to configuration files in various formats, with support for overriding the values based on environment, hostname, locale, or any other arbitrary thing you happen to come up with.

yardocs

Just like everything else these days. In your Gemfile:

gem 'figgy'

Set it up (say, in a Rails initializer):

AppConfig = Figgy.build do |config|
  config.root = Rails.root.join('etc')

  # config.foo is read from etc/foo.yml
  config.define_overlay :default, nil

  # config.foo is then updated with values from etc/production/foo.yml
  config.define_overlay(:environment) { Rails.env }

  # Maybe you need to load XML files?
  config.define_handler 'xml' do |contents|
    Hash.from_xml(contents)
  end
end

Access it as a dottable, indifferent-access hash:

AppConfig.foo.some_key
AppConfig["foo"]["some_key"]
AppConfig[:foo].some_key

Multiple root directories may be specified, so that configuration files live in more than one place (say, in gems):

AppConfig = Figgy.build do |config|
  config.root = Rails.root.join('etc')
  config.add_root Rails.root.join('vendor/etc')
end

Precedence of root directories is in reverse order of definition, such that the root directory added first (typically the one immediately within the application) has highest precedence. In this way, defaults can be inherited from libraries, but then overridden when necessary within the application.

Because the objects exposed by figgy are often hashes, all of the instance methods of Hash (and, of course, Enumerable) are available along the chain. But note that this means you can not use key names such as size or each with the dottable access style:

AppConfig.price.bulk   #=> 100.00
AppConfig.price.each   #=> attempts to invoke Hash#each
AppConfig.price[:each] #=> 50.00

This was written on Enova's dime/time.