enum.rb

# for use by collection_select and friends, to link a human-readable label with a db-friendly symbolic value
# todo: ActiveRecord macros for setters (for allowing multiple values or just one)
# Usage:
# Table name: snacks
#  id                         :integer
#  ice_cream                  :string
# class Snack < ActiveRecord::Base
#   FLAVORS = Enum.new [
#       [:vanilla, "Vanilla"],
#       [:chocolate, "Chocolate"],
#       [:rocky_road, "Rocky Road"]
#       ])
#   ]
# end
# ...
# <%= simple_form_for @snack do |f| %>
# <%= f.collection_select :ice_cream, Snack::FLAVORS, :value, :label %>
# <% end %>

class Enum

  class Item
    attr_reader :value, :label

    def initialize value, label
      @value, @label = value, label
    end

    def ==(other)
      other.is_a?(Enum::Item) and
        other.value == value and
        other.label == label
    end
  end

  include Enumerable

  attr_reader :items

  def initialize item_tuples
    @items = item_tuples.map do |item_tuple|
      Item.new(item_tuple[0], item_tuple[1])
    end
  end

  def each &block
    @items.each &block
  end
end

enum_spec.rb

require 'rails_helper'

describe Enum do

  describe Enum::Item do
    subject { Enum::Item.new(:rocky_road, "Rocky Road") }

    it 'has a human-readable label' do
      expect(subject.label).to eq("Rocky Road")
    end

    it 'has a symbolic value' do
      expect(subject.value).to eq(:rocky_road)
    end
  end

  describe "can be initialized with a list of item tuples" do
    subject { Enum.new([
                         [:vanilla, "Vanilla"],
                         [:chocolate, "Chocolate"],
                         [:rocky_road, "Rocky Road"]
                       ]) }

    it "contains the items" do
      expect(subject.items[0]).to eq(Enum::Item.new(:vanilla, "Vanilla"))
      expect(subject.items[1]).to eq(Enum::Item.new(:chocolate, "Chocolate"))
      expect(subject.items[2]).to eq(Enum::Item.new(:rocky_road, "Rocky Road"))
    end

    it "implements enumerable (with each)" do
      array = subject.items.dup
      subject.each do |x|
        expect(x).to eq(array.shift)
      end
    end
  end

end

Hi, txs for the advise.
Question: where do i put the Enum.rb within rails directory tree ?

@geekjimbo the best place would be /lib folder. If you're running older version of Rails also make sure the lib folder is in the autoload paths.