Simon Willison’s Weblog
YAGNI—You Ain’t Gonna Need It—is a rule that says you shouldn’t add a feature just because it might be useful in the future—only write code when it solves a direct problem.
When should you over-ride YAGNI? When the cost of adding something later is so dramatically expensive compared with the cost of adding it early on that it’s worth taking the risk. On when you know from experience that an initial investment will pay off many times over.
Lukes’s exceptions to YAGNI are well chosen: things like logging, versioning, created_at timestamps and a bias towards “store multiple X for a user” (a many-to-many relationship) if there’s any inkling that the system may need to support more than one.
If you’re building a mobile app that talks to your API, make sure to ship a kill-switch: a mechanism by which you can cause older versions of the application to show a “you must upgrade to continue using this application” screen when the app starts up.
In an ideal world, you’ll never use this ability: you’ll continue to build new features to the app and make backwards-compatible changes to the API forever, such that ancient app versions keep working and new app versions get to do new things.
