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Have you ever been in an old house? Not old, like, on the Historic Register, well-preserved, rich bastard "old house". Just a house that has been around awhile. A place that has seen a lot of living.
You'll find light switches that don't connect to anything; artwork hiding holes in the walls; sometimes walls have been added or removed and the floors no longer match.
Any construction that gets used, must change as needs change. Be it a house or a city or a program, these evolutions of need inevitably introduce complexity and flaws that are large enough to annoy, but small enough to ignore. Over time those issues accumulate until they reach a crisis point. Houses get remodeled or torn down, cities build or remove highways, and programs get refactored or replaced.
You can and should design for change, within reason, because all successful programs will need to change in ways you cannot predict. But the fact that a system eventually becomes complex and flawed is not due to engineering failures - it is inherent in the nature of changing systems.
My 100 year old house has marks on the floor that look like it was worn from a door swinging. Very distinctive arc pattern. Like it was there for many years and was under frequent use.
The problem is that there's no door there, just a wall, which is also the edge of a dormer...so if there were a door there it would just open out onto a sloping roof.
Every time I register it I contemplate why it's there and wtf happened.
There was most likely a closet or other crawl space storage area there. My house has closets like that but luckily full height entries to them so we can actually step in. I’ve seen other houses with 1/2 or 1/3 height doors leading to under-roof crawl spaces for storage.
the fact that a system eventually becomes complex and flawed is not due to engineering failures - it is inherent in the nature of changing systems
it is not. It's just that there will be some point, where you need significant effort to keep the systems structure up to the new demands {1}. I find the debt-metaphor is quite apt [2]: In your scenario the debt accumulates until it's easier to start fresh. But you can also manage your debt and keep going indefinitily. But in contrast to financial debt, paying of technical debt is much less obvious. First of all it is pretty much impossible to put any kind of exact number on it. On the other hand, it's very hard to tell what you actually should do to pay it off. (tangent: This is why experienced engineers are worth so much: (among other things) they have seen how debt evolves over time, and may see the early signs).
[1] https://tidyfirst.substack.com/p/the-openclosedopen-principle
You’ll find light switches that don’t connect to anything
My house was built in the 1960s and had a switch like this. I was always curious what the switch was actually doing. One day, I was replacing all the light switches with smart switches, and discovered that the switch didn't even had a load connected to it! It was literally doing nothing.
I was perplexed by this until I saw some old photos of the house, from the early 2010s when the previous owners bought it. It turned out that there were originally ceiling lights in the room (George Nelson bubble lamps, fitting the mid-century modern design of the house) that were removed at some point, and the switch was left behind. I had an electrician install recessed lights in most rooms, and they found old wires for the old lights. It wasn't actually proper power cabling though... They had used speaker cables to power the lights!
I used to work summers as an apprentice electrician. The amount of crazy wiring I saw in old houses was (heh) shocking. Sometimes it was just that it was old. Real old houses sometimes just had bare wire wrapped in silk. ... And a few decades later that silk was frayed and crumbling in the walls and needed replacing.
My current house was wired at a time when copper was more precious, so it was wired up and down through the house, with circuits arranged by proximity, not necessarily logic. When a certain circuit in my house blows the breaker, my TV, PC and one wall of the master bedroom all lose power. The TV and PC are not in the same room either.
in the 80s I helped gut a house that had aluminum wire with paper thin cloth wrapping. anywhere you touched it it would just disintegrate. blew my mind that the place hadn't burned to the ground, especially all the dead rodents that had nested in the piles of fragmented cloth wrap.
You can and should design for change, within reason, because all successful programs will need to change in ways you cannot predict
You've yourself here. You can not predict how it wull change. Which means that whichever design for change you've made, may just as well completely miss the future utilization
Which doesn't mean that we shouldn't design for change at all... Just saying.
You can build your systems with as few assumptions as possible. The fewer assumptions you make, the less probable it is that any of your future assumptions will conflict with your previous assumptions. Your code will be built for change.
If your API call to some external system assumes the existence of a particular button in the UI, then your system isn’t built for change. Maybe you want to change this button? Then you need to go through all places in the code that relies on this particular button to see if it doesn’t conflict with any of their assumptions.
As long as loose coupling, and separation of concerns are well tinkered into your application you minimise risks of breaking everything on a restructuring.
If you have for example shared state leaking everywhere into the program, your most probably doomed on the slitest changes.
I am not saying you're wrong, but there are ways to mitigate the risks even without knowing what will happen in the future.
Just saying.
.... Saying what, exactly?
I said that we should
- design for change
- "within reason"
- because we can't know what exact changes are needed.
And you argued... The same thing? Just in the reverse order?
Seems like he's worried you'll Java everything up, which can be valid.
I think a good, easy example is whether your application should allow a selection of databases or be tied to one database.
You can make arguments for either, often (but not always) regardless of your use case.
You can design it to be changeable at all, though.
In the simplest case that's just proper abstractions. You can't change details in the rest controller, if the persistence layer absolutely needs to call methods from the rest controller for no reason.
Finding the right balance between YOLO and YAGNI is almost impossible to get right. But you can at least try not to land on the extremes.