has_statuses.rb

module HasStatuses

  def has_statuses(*statuses)
    self.const_set "Statuses", Module.new
    statuses.each { |status| self::Statuses.const_set status.to_s.upcase, status }
    self.const_set "ALL_STATUSES", self::Statuses.constants.collect { |constant| self::Statuses.const_get(constant) }
  end

  Object.send :extend, self

end

class Task

  has_statuses :new, :in_dev, :done

end

puts Task::Statuses.constants.inspect   # => [:NEW, :IN_DEV, :DONE]
puts Task::Statuses::NEW                # => :new
puts Task::Statuses::IN_DEV             # => :in_dev
puts Task::Statuses::DONE               # => :done
puts Task::ALL_STATUSES.inspect         # => ["new", "in_dev", "done"]