Distinctions With A Difference

At first, programming is just programming. You think of a thing. You make the computer do it. 🎉

After a while, you notice that not all programming is the same. Deja vu sets in. “I’ve done this before.” (Also the basis for patterns.)

Empirical Software Design book series presents a series of these distinctions. (I think of them as “two hats”. Merch opportunity💰.)

• Reversible versus irreversible. Some changes are easily reversed. Make these quickly & with confidence. Other changes have consequences for the larger system. Make these only after double checking. Converting irreversible changes (even partly) into reversible changes creates value.

• Structure versus behavior. Structure changes are mostly reversible. Behavior changes are likely irreversible (e.g. reporting different answers to tax authorities) & require multiple feedback loops. Separating behavior changes from structure changes creates value.

• Safe versus unsafe. Some changes have little to no risk of accidentally changing behavior elsewhere in the system. Converting unsafe changes into a succession of safe changes creates value.

• Personal versus team. Some changes, like tidying first, mostly affect folks making those changes. Others, like an API change, affect other programmers. Learning to slice, stage, & socialize externalities creates value.

• Changer versus waiter. At a larger scale, some structure changes don’t affect delivery of value to those waiting for features. Others affect non-programmers—”We’re going slow down for a bit while we tidy this mess up.” Converting interruptive changes into a sequence of flow-maintaining changes creates value.

• Interface versus implementation. Changes to an interface ripple to all invokers. Changes to an implementation are contained (ideally—see safe versus unsafe above). Only changing one at a time reduces risk, improves flow, and creates more value.

• Tidy first versus tidy after (or later, or never). Timing of design changes is as important as the resulting structure. Pay attention to the time value of money & the (often opposing) optionality of the system.