has_behavior.rb

has_behavior :supports_groups_and_categories

def has_behavior(behavior)
  mod = behavior.to_s.camelize.constantize
  class << mod
    def class_methods
      mod::ClassMethods
    end
    def instance_methods
      mod::InstanceMethods
    end
  end

  include mod.instance_methods
  extend mod.class_methods
end