rails/activesupport/lib/active_support/ordered_options.rb

# OrderedHash is namespaced to prevent conflicts with other implementations
module ActiveSupport
  class OrderedHash < Array #:nodoc:
    def []=(key, value)
      if pair = assoc(key)
        pair.pop
        pair << value
      else
        self << [key, value]
      end
    end

    def [](key)
      pair = assoc(key)
      pair ? pair.last : nil
    end

    def keys
      collect { |key, value| key }
    end

    def values
      collect { |key, value| value }
    end
  end
end

class OrderedOptions < ActiveSupport::OrderedHash #:nodoc:
  def []=(key, value)
    super(key.to_sym, value)
  end

  def [](key)
    super(key.to_sym)
  end

  def method_missing(name, *args)
    if name.to_s =~ /(.*)=$/
      self[$1.to_sym] = args.first
    else
      self[name]
    end
  end
end