Say it, don't build it: the patterns you leave out

transcript

You are twenty minutes into a coupon round. The design is working. Should you add State and Command, just to be complete?

Saying it takes ten seconds, and shows you saw the pattern. Building it takes ten minutes, and gives the interviewer a class to question.

State stayed out. A coupon is on or off in the catalog. That's one flag. If it grew to draft, live, paused, and expired, a table would come first.

Command stayed out. Nobody asked to take a coupon back. If cancelling an order must give the coupon back, now it comes in.

Factory stayed out too. The catalog is written in code, so the constructors are the registry. Facade stayed out. The engine is already the one door. Each has a trigger.

For each pattern you leave out, name the requirement that would bring it in. That shows judgement, without adding a line of code.

Full breakdown in the lecture.