README.md

!!! I HAVEN'T RUN THIS CODE !!!

Refactor of Caleb Wood's module approach to static lists in Rails to extract StaticList from Greeting.

snippets.rb

# lib/static_value.rb
class StaticValue < Stuct.new(:id, :name)
  alias :to_s :name
end

# lib/static_list.rb
module StaticList
  extended do |list|
    def list.all
      constants.map do |constant_name|
        const_get(constant_name)
      end
    end

    def list.form_options
      all.map do |static_value|
        [ static_value.name, static_value.id ]
      end
    end

    def selected(static_value_id)
      all.detect do |static_value|
        static_value.id == static_value_id
      end
    end

    def list.valid_ids
      all.map(&:id)
    end
  end
end

# app/models/concerns/greeting.rb
module GreetingList
  extend ActiveSupport::Concern
  extend StaticList

  HI    = StaticValue.new(1, 'Hi')
  HELLO = StaticValue.new(2, 'Hello')
  DEAR  = StaticValue.new(3, 'Dear')
  OTHER = StaticValue.new(4, 'Other')

  included do
    validates :greeting_id, presence: true,
                            inclusion: { in: Greeting.valid_ids }
  end

  def greeting
    GreetingList.selected(greeting_id)
  end
end

# app/models/person.rb
class Person < ActiveRecord::Base
  include GreetingList
end

Refactor opportunities:

• Instead of assigning StaticValues to constants, add a hook method to StaticList that collects the values: add_value StaticValue.new(1, 'Hi'). The refactor the generated methods to read from the hook instead of constants. I probably wouldn't do this if even on value needed to be special (GreetingList::OTHER).
• Get fancy with method_missing to emulate more features from Rails' enum.
• Memoize generated methods with instance variables.