Enumerations in ruby

Enumeration.rb

# credit goes to http://stackoverflow.com/questions/265725/what-is-the-best-way-to-handle-constants-in-ruby-when-using-rails
class Enumeration
  def self.def_enum(key,value)
    @hash ||= Hash.new { |hash, key| raise NameError, "#{self.name}::#{key} is not defined" }
    @hash[key] = value
  end

  def self.const_missing(key)
    @hash[key]
  end

  def self.each
    @hash.each {|key,value| yield(key,value)}
  end

  def self.hash
    @hash
  end

  def self.values
    @hash.values || []
  end

  def self.keys
    @hash.keys || []
  end

  def self.[](key)
    @hash[key]
  end
end

example.rb

class Color < Enumeration
  self.def_enum(:RED, '#f00')
  self.def_enum(:GREEN, '#0f0')
  self.def_enum(:BLUE, '#00f')
end

Color::RED    => '#f00'
Color::GREEN  => '#0f0'
Color::BLUE   => '#00f'

Color.keys    => [:RED, :GREEN, :BLUE]
Color.values  => ['#f00', '#0f0', '#00f']