Add one chat line, edit three working files

transcript

Priya adds one chat line to a group order screen. It should say, Ben joined. She has to edit three classes that already work. A slip in any one breaks the others.

Four widgets. Each one holds the others it needs. Count the arrows. Nine. Four classes could hold twelve. Six could hold thirty.

The chat needs a call from three classes. The roster, the cart, the pay desk. Nine references become twelve. Through a room, it's one line in one class. The other three never change.

Give the parts one room. Each part tells the room what happened. No part knows another part exists. The rules live in the room, written once.

Nine references between widgets before. None after. And one class to read when a rule breaks.

The room doesn't make the rules simpler. It makes them easy to find. That's the trade.

Full breakdown in the lecture.