gistfile1.txt

directory structure
app/
  lib/
    core_ext/
      hash.rb
    core_ext.rb

In config/application.rb:
config.autoload_paths += %W(#{config.root.join}/lib)

In lib/core_ext.rb
raise 'LOADED'                                                                                                                            
require 'core_ext/hash'

In lib/core_ext/hash.rb
class Hash                                                                                                                                         
  # allow to pass multiple keys, useful for nested hashes.                                                                                         
  # Ex: h = { :a => { :b => { :c => 42 } } }                                                                                                       
  # h.r(:a, :b, :c) => 42                                                                                                                          
  def r(*args)                                                                                                                                     
    v = self[args.shift]                                                                                                                           
    if args.empty?                                                                                                                                 
      v                                                                                                                                            
    elsif v.is_a?(Hash)                                                                                                                            
      v.r(*args)                                                                                                                                   
    else                                                                                                                                           
      nil                                                                                                                                          
    end                                                                                                                                            
  end                                                                                                                                              
end