A demo of YAML anchors, references and nested values

stooge_loader.rb

require 'rubygems'
require 'yaml'

# A demonstration of YAML anchors, references and handling of nested values
# For more info, see: 
#   http://atechie.net/2009/07/merging-hashes-in-yaml-conf-files/

stooges = YAML::load( File.read('stooges.yml') )
# =>  {
#             "default" => {
#                     "URL" => "stooges.com",
#             "throw_pies?" => true,
#                 "stooges" => {
#                 "larry" => "first_stooge",
#                   "moe" => "second_stooge",
#                 "curly" => "third_stooge"
#             }
#         },
#         "development" => {
#                     "URL" => "stooges.local",
#             "throw_pies?" => true,
#                 "stooges" => {              # where are the other 3 stooges?
#                 "shemp" => "fourth_stooge"
#             }
#         },
#                "test" => {
#                     "URL" => "test.stooges.qa",
#             "throw_pies?" => true,
#                 "stooges" => {
#                 "larry" => "first_stooge",  # all stooges are here because...
#                   "moe" => "second_stooge", # ...we used `stooges: <<: *stooge_list` in stooges.yml
#                 "curly" => "third_stooge",
#                 "shemp" => "fourth_stooge"
#             }
#         }
#     }

stooges.yml

default: &DEFAULT
  URL:          stooges.com
  throw_pies?:  true  
  stooges:  &stooge_list
    larry:  first_stooge
    moe:    second_stooge
    curly:  third_stooge
  
development:
  <<: *DEFAULT
  URL:      stooges.local
  stooges: 
    shemp: fourth_stooge
    
test:
  <<: *DEFAULT
  URL:    test.stooges.qa
  stooges: 
    <<: *stooge_list
    shemp: fourth_stooge

very_simple_app_conf.rb

# Set custom config options in config/app_cong.yml
# @examples: 
#   AppConf.use_ssl?                  # => false
#   AppConf.site_color                # => "purple"
class AppConf
  SETTINGS_HASH = YAML.load_file( Rails.root.join('config', 'app_conf.yml') )[Rails.env]  
  
  class << self
    def method_missing(method, *args)
      SETTINGS_HASH[method.to_s]  # could use ClassyStruct here for more features and better performance
    end
  end
end

Thanks for your nice clean example of this.

a lot of thanks

Yeah, thanks so so much! I wasn't sure how to get round the lack of deep mergingin yaml, but your strategy totally solved it for me :)

Good example, much appreciated.

Is there a <<: *DEFAULT operator that works with arrays?

@fulldecent: not, it shouldn't work with array. See YAML refcard for spec 1.1.

<< : Merge keys from another mapping.

Thanks for this @bowsersenior.
@fulldecent I've managed to do with final arrays via:

default_array: &DEFAULT_ARRAY
  - item_1
  - item_2

my_array: *DEFAULT_ARRAY
my_other_array:
  - item_3
  - item_4