It's a very common practice in Ruby to use Module mixins to enhance the functionality of a class. In fact, one of the most powerful and useful features of the Ruby language is that it is so easy to do so. Great stuff all around.

Another common pattern, however, is to want to provide some include-time configuration when the module is mixed in. Let's imagine I'm writing an extension for ActiveRecord that creates a slug based on some field. What I want in the end might be something that looks like this: