model_extensions_loader.rb

class ModelExtensionLoader
  def self.activate!
    class << ActiveRecord::Base
      alias_method :old_inherited, :inherited

      def inherited(model)
        puts "Trying to load extensions #{model} extensions"
        if extension = ModelExtensionLoader.safe_constantize("Extensions::#{model}")

          model.send(:include, extension)
          puts "Included instance methods"

          if class_methods = ModelExtensionLoader.safe_constantize("Extensions::#{model}::ClassMethods")
            model.send(:extend, class_methods)
            puts "Extended class methods"
          end
        end

        old_inherited(model)
      end
    end
  end
  
  def self.safe_constantize(name)
    begin
      return name.constantize
    rescue NameError => name_error
      raise name_error unless name_error.message == "uninitialized constant #{name}"
    end
  end
end

ModelExtensionLoader.activate!