lookups.rb

module Lookups

  # Allows the definition of lookup values in a class.
  def define_lookup(klass_name, lookup_codes)

    # Ensure the classname conforms to convention
    klass_name = klass_name.to_s.classify

    # Add class methods
    klass = Class.new do

      cattr_accessor :codes

      # Allow access using LookupName.code(:the_code)
      def self.code(code)
        send(code.to_s)
      end

      # Get the translation for the code
      def self.human_name(code)
        class_names = name.gsub('::','.').underscore
        I18n.t("lookups.#{class_names}.#{code}")
      end

      # All of the types for use in a form select list
      def self.select_list
        codes.map { |code| [human_name(code), code] }
      end
      
      # Check that the given type exists
      def self.valid_type?(code)
        codes.include?(code.to_s)
      end

      # Allow the use of LookupName.lookup_code (for example)
      def self.method_missing(method, *args, &block)
        return method.to_s if valid_type?(method)
        super
      end

      # Always have a respond_to with a method missing!
      def self.respond_to?(method)
        return true if valid_type?(method)
        super
      end

    end

    # Assign the class to its name
    self.const_set(klass_name, c)

    # Set the codes
    klass.codes = lookup_codes

  end
end

# Usage example

class FooBlah
  extend Lookups
  
  # To define a lookup
  define_lookup "RecurrenceType", %w(minutely hourly daily weekly monthly yearly)
  define_lookup "RepeatUntilType", %w(forever to_date occurrence_count)
  
  def something
    puts RecurrenceType.weekly
    # Or
    puts RecurrenceType.code(:weekly)
    # Or referencing from outside the class
    puts FooBlah::RecurrenceType.weekly
  end

  ...
end

# To use in all AR classes, put in an initializer:

ActiveRecord::Base.extend Lookups

# In forms it can be used in select lists like this:

<%= f.select :recurrence_type, FooBlah::RecurrenceType.select_list %>

Thanks Tom. I've reviewed mine and changed to a module now. The original was a mess!