A gem I plan to write

enum.rb

module Enum
  def self.included(base)
    #TODO: learn difference between extend and include (send :include, )
    base.extend ClassMethods
    super
  end

  module ClassMethods
    def enum(args)
      # Constants
      args.each do |name, array|
        fields = array.collect do |key, value|
          "['#{key.to_s}', #{key.to_s.upcase} = '#{value}']"
        end.join(', ')
        _module.module_eval "#{name.to_s.upcase} = [#{fields}]"
      end
      # Etc...
    end

    #TODO: better understand this
    def _module
      @_module ||= begin
        mod = Module.new do
          @_class_methods = Module.new
          class << self
            attr_reader :_class_methods
          end
        end
        include mod
        extend mod._class_methods
        mod
      end
    end
  end
end

class Test
  include Enum

  enum numbers: {one: 'Uno', two: 'Dos', three: 'Tres'}
  # defines NUMBERS = [['one', ONE = 'Uno'], ['two', TWO = 'Dos'], ['three', THREE = 'Tres']]

  def initialize
    puts ONE
    puts TWO
    puts THREE
  end
end

Test.new
# Uno
# Dos
# Tres