One day, Sandi Metz was pressed by a team she was working with to produce a simple set of rules that would lead to better code quality. After consideration, she came up with the following surprisingly numerical guidelines: classes can’t grow beyond one hundred lines of code, methods can’t grow beyond five lines of code, methods can only take four parameters (hash options count), and controllers can only send one message to one object.
What emerges from these rules is a pretty pragmatic lens on how to practice object oriented design with Ruby and Rails without falling into the tarpit of more radical approaches. You don’t end up needing to worry about fast tests, decoupling from the framework, presenter, conductors, mediators, adapters, ad nauseum.
More critically, you aren’t beset with decision fatigue. You don’t have to survey the landscape of helper gems and bolt-on approaches to writing Rails applications. You can start with the way Rails wants you to write applications: logic and data encapsulated in models, behavior encapsulated in controller actions, easy sharing of data between actions and views with instance variables, etc.
You start with what Rails wants; when you find yourself violating one of Sandi’s rules, then you apply design and refactoring techniques. If a model does too much, extract common behaviors into an encapsulated object. If a controller action knows about too many things, move that into an object and call it from the action. You can go a really long way using only the Replace Method with Method Object refactoring until you get to Kent Beck’s notion of a Composed Method.
That bears repeating. In big letters.
Most Rails applications can be made better by relentless application of Method Object and Composed Method.
Thoughtbot has written about what this looks like as it emerges. It doesn’t have to involve a lot of pattern names, new frameworks, framework asceticism or half-baked conventions. You write classes and methods when needed. When they get too big, you refactor, rinse, and repeat.
Sandi’s book, Practical Object Oriented Design with Ruby, is great not because it covers new territory or casts a new light on the subjects of object oriented programming and Ruby. It’s great because it shows how you work with the tools provided by OO and Ruby. It’s great because it shows how you go from less-good code to more-good code.
It’s really great because its short and easy to read. This is the book that enthusiastic, “enlightened” programmers can hand to the less energetic to help them understand how to write better code. They can do so without worrying that the book is hard to understand or a beast to read. It’s as close to a magic pill for clue enhancement as anyone has yet come.