if not String.method_defined? :to_underscore
  class String
     # ruby mutation methods have the expectation to return self if a mutation
     # occurred, nil otherwise.
     # (see http://www.ruby-doc.org/core-1.9.3/String.html#method-i-gsub-21)
     def to_underscore!
       gsub!(/(.)([A-Z])/,'\1_\2') && downcase!
     end

     def to_underscore
       dup.tap { |s| s.to_underscore! }
     end
  end
end