Non-Atomic Refactoring and Software Sustainability

Sustainability is the ability of a project / codebase / organization to react to necessary changes over its expected lifespan. At a large enough scale, or with enough disconnect between dependencies, sustainability comes from application of both technical and non-technical approaches. On the technical side, I advocate for restraint among API providers on making arbitrary changes, and use of non-atomic refactoring techniques when more invasive changes are required; such techniques are employed in many Google projects, and in programming languages like Go and C++, to allow more flexible changes to language standards over time. On the non-technical side, I argue for a clear separation of responsibilities (providers need to do the bulk of the work for the update), as well as a growing need to document acceptable usage of an API, be it a library or programming language. In many languages, there are very few changes to an API that are provably safe without this idea: just because a user's code currently works does not mean that it is supported and can be expected to continue to work indefinitely under maintenance. Taken together, these two approaches form what I believe to be a minimum set of requirements when approaching software sustainability.