instance class variables

gistfile1.rb

module Validator
  def self.included(klass)
    klass.extend ClassMethods
  end

  module ClassMethods
    def inherited(child_class)
      child_class.instance_variable_set :@required_fields, self.required_fields
    end

    def add_required_fields(*fields)
      @required_fields = required_fields + fields
    end

    def required_fields
      @required_fields || []
    end
  end
end

# so I can do something like

class MyBase
  add_required_fields *%i(a b c)
end

class MyChild < MyBase
  add_required_fields *%i(d e f)
end
# for MyChald result would be a b c d e f


class TheOtherChild < MyBase
  add_required_fields *%i(g h i)
end
# for MyChald result would be a b c g h i