YAGNI stands for “You Aren’t Gonna Need It”. This is an acronym I’ve only taken to heart recently, despite reading about design principles on and off over the past few years. I have learned enough from my mistakes in the early days of programming to know that planning pays off, and what could be better planning than adding code now to help yourself add things in the future? Two words: clean code.
This summer, I was tasked with designing and implementing a desktop application from scratch, as the only developer. The specification was vague (essentially, “these are the user inputs, this is the output, and leave room to add more inputs and outputs later”) and it required research into topics that have nothing to do with software, that I had never seen before. This caused me to create unnecessary abstractions and extra features in many places, just in case. In the end, I refactored quite a bit once I understood more about what was required and realized what wasn’t needed. The extensibility that I actually needed worked out great. Everything else got in the way.
A blog post on YAGNI by Martin Fowler does a great job of describing what I did wrong, and I chose it in order to learn how I could have improved what I did. His summary of YAGNI is that features you expect to need should not be built. Features should be built only when you actually need them, because it’s very likely that “you aren’t gonna need it”.
Fowler goes on the describe the main argument YAGNI makes, which is that you might be wrong about presumed features. When you’re wrong about features, you accrue four costs: the cost of building a presumptive feature, the cost of delaying other features, the cost of carrying the presumptive feature (making it harder to modify other code), and the cost of repairing the presumptive feature (because even unused features must be maintained).
One major point that Fowler stresses is that this does not apply to efforts to make code extensible, unless it adds unneeded complexity. There is a difference between adding code that is easy to refactor in the future, and adding unused code. The former follows other design principles. The latter adds clutter and creates confusion. And who needs more of that?
Could I have done better with the aforementioned project? I think so. There were a couple major overhauls that would have been a nightmare without some extensibility baked in, but most of that code didn’t add unnecessary complexity and is therefore in line with YAGNI. I also have to consider that it was a single-person project done in 3 months, so it is likely that the negative side-effects were kept at a minimum. It’s also impossible to determine how much time I spent searching through unnecessary code, so a little more YAGNI could have sped things up. In the future, I’ll be considering this important design principle.