Regenerative Software

Chapter 2. Replaceability as the Defining Property

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We set out to replace what looked like the simplest important thing in Wunderlist.

I’ll call it group memberships. That isn’t quite what it was, and the real name doesn’t matter. What matters is that it was two things at once: central to how the product worked, and small enough that replacing it felt like a chore rather than a project. A few of us could read the whole thing in an afternoon. We had read it. We gave the replacement an afternoon.

The trouble was never in group memberships. It was in how the rest of the system found things. We had built our own unique-ID system, the kind of decision that makes sense at 3 a.m. in year one and then follows you for the life of the company. Every entity in Wunderlist drew its ID from it, and every part of the system that needed to point at another part’s data resolved those IDs through machinery that, by the time we went to touch group memberships, almost nobody fully understood. It had accumulated assumptions about uniqueness, ordering, and how references resolved ...