Introduction to capability objects. Also a discussion of how to use these to improve the effective purity of functions. All with the aim to improve modularity in your programs. http://insights.workshop14.io/2016/05/01/purify-your-programs-with-capability-objects.html

All examples are in JS but the discussion is valuable to all languages with easy global access to many capabilities. Ruby is definitely one of those and I personally use this technique frequently in my ruby code.