The cost YAGNI was never about

https://newsletter.kentbeck.com/p/the-cost-yagni-was-never-about

by kiyanwang • 24 days ago

131 142 24 days ago

newsletter.kentbeck.com

phamilton6• 24 days ago

The cost of restructuring has also gone down.

The cost of shoring up behavior with tests ahead of a restructure has gone down because of AI.

The cost of implementing a zero downtime migration has gone down because of AI.

A big part of the rust hype has been the low cost of restructuring within an application, even before AI. And now even more so.

The opportunity cost of not being able to safely restructure has gone up substantially.

This is the number one thing I optimize for now: the ability to quickly and safely change significant parts of the code and product.

cassianoleal3• 24 days ago

This is the number one thing I optimize for now: the ability to quickly and safely change significant parts of the code and product.

This was always a good thing. Its value has nothing to do with the advent of AI coding.

The opportunity cost of not being able to safely restructure has gone up substantially.

This bit is contradictory with everything else you said. Prior to AI coding it would take a lot longer to perform restructures. If anything, the thing you're now optimising for has gone down in value. It's still valuable, but perhaps a little less.

phamilton6• 24 days ago

I'm not talking about time. I'm talking about safety. The amount of times I've seen "I refactored it, but I'm not confident enough to take it to prod" is significant. Being able to go faster but still not ship it is the huge opportunity cost.

mohamedkoubaa• 24 days ago

Ironically, AI assisted/generated code is not trending in the direction of the ability to safely and quickly change. Especially when piloted poorly

xboxnolifes• 24 days ago

> This is the number one thing I optimize for now: the ability to quickly and safely change significant parts of the code and product.
This was always a good thing. Its value has nothing to do with the advent of AI coding.

The value of type safe code did not go up, the cost of development speed has gone down.

samrus• 24 days ago

Your increasing thrash betting that AI will fix it for you. The only thing your getting in return is not having to think that hard.

It doesnt cost that much time or effort to think hard, so you will be outcompeted by people levergaing AI as much as you, but thinking enough to not have it be thrashing around

6510• 22 days ago

It doesnt cost that much time or effort to think hard

If you manage to avoid effort and thinking long enough it will get harder.

rednb• 24 days ago

the ability to quickly and safely change significant parts of the code and product.

Hum, this reminds me something... "O: open to extension, closed to modifications". Old things are new again.

From context efficiency with approaches such ad DDD and clean architectures, all the way to items such as this one, AI is not creating new tradeoff, it just acts as a multiplier, multiplying productivity for teams doing things right, and multiplying debt for teams having a low quality bar as far as design and architecture are concerned.

rzmmm• 24 days ago

Over the last couple months I've seen the debt multiplication in some OSS projects. It's like premature aging of a codebase.

phamilton6• 24 days ago

Old things are new again.

This is exactly how I've felt. I've read some many old papers and books and found great techniques that are even more applicable than ever.

lmm• 24 days ago

The cost of restructuring has also gone down.
The cost of shoring up behavior with tests ahead of a restructure has gone down because of AI.

Disagree. The growth in brittle AI-generated tests means restructuring is more costly than it was before. Pruning your test suite so that it tests the essence of the problem and not the incidental design decisions is something AIs aren't yet capable of.

chowells• 24 days ago

Oh, it's worse than that. I've seen a rise in mutation testing, intended to ensure any change in implementation is caught by tests. Think about that for a moment. It's giving a fancy name to creating brittle tests than fail if any line of code is changed.

And this is seen as a good thing, because LLMs are really bad at confining their changes appropriately. Testing is really in a dark place right now.

majormajor2• 24 days ago

The cost of shoring up behavior with tests ahead of a restructure has gone down because of AI.

Yes.

But the ease of not doing that and instead just getting a brittle set of three-quarters-baked tests is extremely high! And many people seem happy to go from "a few human-written mediocre brittle tests" to "a bunch of AI-written mediocre brittle tests" because it is an objective improvement and the people who weren't avoiding speculative structure and looking for the write boundaries before are happy to also not do so no.

So completely agree with the "take advantage of the tools this way" but I also wouldn't claim it's a reason to no longer worry about if you're building the wrong castles in the sky too early, because perfect refactor-proof testing contracts are still usually pretty hard to design.

phamilton6• 24 days ago

perfect refactor-proof testing contracts are still usually pretty hard to design

Not sure about hard, but definitely rare and we as an industry are under-skilled in these areas.

We have decades of research and tools for testing and verification of software. Property tests, dependent types, formal verification and proof, etc. The paths have been there, we have just collectively prioritized other things.

It requires an intentional shift in how we design and build. That shift is the harder part.

ffsm8• 24 days ago

The cost of implementing a zero downtime migration has gone down because of AI.

You either don't know what that technical term means or you're just wrong. AI does not meaningfully move the needle on that. It only makes backwards compatible deployments easier insofar you're able to do the overhead for splitting the change with less effort then before.

phamilton6• 23 days ago

I've always known how to do zero downtime migrations. The question has always been "Is the engineering cost worth it?"

It only makes backwards compatible deployments easier insofar you're able to do the overhead for splitting the change with less effort then before.

Yes. That reduces the cost of implementing them.

To be clear, I'm not talking about "Split my db migration and my code that depends on the new table". I'm talking about things like "Set up dual writes between an old database schema and a new database schema with a thorough test suite and do shadow reads against both datasets in prod to do differential testing". That's nontrivial engineering effort that would definitely warrant a discussion in the past. Today we just do it. It's fast and lowers risk.

sebastianconcpt• 24 days ago

Seeing running software as an asset is the right approach.

But the costs of executing and even re-doing things went significantly down.

The costs that didn't went down are the ones of breaking the chain of trust to a predictable outcome. A specific version of some running software accumulated trust. If you rewrite it from scratch that capital is reset on release.

zephen8• 24 days ago

Nothing I have read by Kent Beck has ever suggested that he would be useful in a chip company, where lots of people toil for a long period of time in order to produce something that no customer can possibly see until it's finished, and that must be sold in quantities of millions in order to make money.

marifjeren4• 24 days ago

Interesting. How do chip companies plan such projects? Do they use agile, waterfall, or some other non-software-industry frameworks?

ajb2• 24 days ago

They (or at least some of them) use waterfall - the real waterfall, not the bogeyman invented by agile consultants.

zephen8• 24 days ago

(Some) chip companies have jumped on the agile bandwagon for (some) tasks.

It's always interesting to read about some chip company or another making some agile move, when the reality is that they were already doing about as many agile things as possible before agile was a thing. (For example, a management commitment to "shift left" when they have always been about significant up-front testing and feedback.)

In many, if not most, cases, the testing software is so huge that at least some of it needs to be tested itself. That can certainly benefit from agile.

But the overall process more resembles traditional waterfall. You have several definite final endpoints, and although you can make subsequent changes, those are expensive. Also, you have a silicon budget, and a pin budget, and a heat and power budget. At the end of the day, you are producing something physical with real-world physical constraints that (a) cost real money, and (b) can't be altered by just telling your customer to add more RAM or a bigger processor.

Also, in general, although designers will write their own little unit tests for a few things, it is best practice to insure that the real tests are performed by internal organizations that are different than the organization the designer is in.

I think that subconsciously, he truism that it is easier to work with and reason about a system that is already working, and to keep it working, than to get it working at all to begin with, drives a lot of the methodology.

The designer might focus on tests to insure that things work well enough to see some results, so things can be hooked up and system tests performed earlier. In one sense, this is a shift left -- the validation people and the people writing software for the chip can get started sooner than they would have otherwise, even if it's a bit frustrating because not everything works off the bat.

But the real torture tests are typically written by the dedicated verification and validation teams. Those are really different skills than design.

fmbb3• 24 days ago

Well he makes software and writes about software development doesn’t he?

Hardware has some hard limitations. The reason software was even invented at all was precisely to escape those limitations.

zephen8• 24 days ago

Well he makes software and writes about software development doesn’t he? Hardware has some hard limitations.

Right.

The reason software was even invented at all was precisely to escape those limitations.

But the methods which are useful for hardware are also often useful for software. Most of the useful parts of agile were already practiced well before that was a name for anything. And the demonization of the straw-man version of waterfall in order to sell more agile consulting has led to some serious misconceptions of what waterfall really is and what it is really capable of and useful for.

The initial impetus for what became known as TDD was software maintenance, and it makes sense there.

But most TDD practitioners are nowhere near as good at real testing as the waterfall test practitioners who understand that a single missed testcase could delay a $10 million project by six months.

And this is why, even in the realm of software you still see serious efforts for aviation and nuclear power plants, and other things with real-world consequences, using more traditional methods.

toast0• 24 days ago

no customer can possibly see until it's finished

I'm sure lots of chip companies don't share their work in progress, but it's not impossible. Sharing simulations and prototypes and engineering samples can and does happen. You've typically got to be a big customer, of course.

But yes, insights for an industry with relatively small costs for change don't apply easily to an industry with large costs for change, and often vice versa.

zephen8• 24 days ago

You've typically got to be a big customer, of course.

Yes, if you're a big enough customer, you might essentially be part of the design team.

Sharing simulations and prototypes and engineering samples can and does happen.

Simulations aren't the thing. They don't go fast enough to solve anybody's problem. To your point, if a customer is part of the design team, then yes, they can, at that point, help to debug, or possibly even get started on their own dependent designs. (Part of the shift-left I talked about in another comment.)

I'm not sure what you mean by "prototypes" but "engineering samples" are essentially the finished product, done after all the work I described.

Yes, they may have bugs (or they might just not have passed validation and ESD testing yet), but that doesn't alter the fact that a waterfall effort happened before they were delivered.

But yes, insights for an industry with relatively small costs for change don't apply easily to an industry with large costs for change, and often vice versa.

The problem with indiscriminate use of agile is that, while, yes, the software industry has relatively small costs for change, it has traditionally had huge costs for the initial delivery, and many agile proponents don't properly segregate those two cases.

If LLMs live up to their apparent promise, then, of course, the equations around the huge costs for the initial delivery could change dramatically.

Of course, the same LLM promise means that the strict definition of TDD (tests written first) is also irrelevant, and perhaps even counterproductive.

geetee• 24 days ago

[flagged]

mh2266• 24 days ago

I fed it into Pangram and it came back as "70% AI generated".

I do feel it's better than some of the pure slop out there, but it still feels pretty sloppy. And I know that this author can write, so if this really was partially done with AI, it's disappointing.

svat• 24 days ago

I think it's the latter. I find the introduction (written by Kent Beck) easier to understand than the rest of the article (which he says is AI-written: "genie-generated description of YAGNI").

In particular writing like this is just annoying:

Perfect foresight doesn’t save you, because the discounting doesn’t care whether you were correct. It cares that you sequenced the cost ahead of the return. The gap between the two is the loss, and you opened the gap on purpose.

saulpw• 24 days ago

This sounded like generated text to me. "The gap" etc

temp_praneshp• 24 days ago

[flagged]

dang2• 24 days ago

You can't post like this here, and we ban accounts that do, so please don't.

https://news.ycombinator.com/newsguidelines.html

gste2• 24 days ago

Yes the more I read it, it's not a cohesive argument. Some of it seems contradictory. It's a word soup with lots of compelling sentences.

antonvs2• 24 days ago

This article is mostly AI slop. It’s very recognizable, and that’s probably what you’re picking up on in other articles as well, because it’s everywhere right now.

rkachowski• 24 days ago

I don't know what happened to Kent Beck, a few of his recent articles seem to be devoid of substance.

simoncion• 24 days ago

Given the disclaimer in TFA, I have to wonder if this subthread is a fine honeypot for bots.

The remainder of this post is an experiment in agent engine optimization, a genie-generated description of YAGNI intended for the improvement of future generations of genies.

marifjeren4• 24 days ago

This is not an argument that prediction is hard, as if a sharper architect escapes it.

I disagree with this. The argument _only works_ if prediction is hard.

disfictional• 24 days ago

Even a correct guess leaves you worse off than not committing.

Similarly, this is also confusing. If I scaffold a highly-likely feature and everything lines up, I ship the feature faster. My team isn't guaranteed to grow or even maintain our headcount, so scrambling to account for YAGNI close to the deadline feels worse than congratulating ourselves on our restraint.

dingdingdang• 24 days ago

Honestly think a lot of this article is ai babble - check how it ends on several classic ai negative triples such as "you’ll pay both bills on it just the same — plus you’ll comprehend it less, because you didn’t write it." ... etc.

skybrian3• 24 days ago

Kent Beck compares unwritten code with a financial option to buy something at a given price.

But that's just an analogy, and it can be taken too far. If you haven't written any code, do you have infinite options? You haven't spent any time yet, but still, that doesn't seem quite right. It might be used to justify staying in the planning stage and putting off writing code indefinitely, to avoid committing to anything.

Why might the analogy work anyway?

Maybe the cost is reading the code? Code that hasn't been written doesn't need to be read. And if you're using a coding agent, it doesn't clutter up the context with irrelevant detail.

Also, code that hasn't been written yet doesn't need testing. Tests you haven't written yet don't take any time to run.

These are good reasons to try to keep a project as small as possible. By putting off features, you delay codebase growth as long as you can.

This suggests that you can avoid a lot of costs by running someone else's code. If you can use a standard API then you don't need to understand the implementation in detail or run its tests. But there are risks to adding dependencies.

skydhash22• 24 days ago

Kent Beck compares unwritten code with a financial option to buy something at a given price.

From Kent's "Tidy, First?"

  Software creates value in two ways:
    What it does today
    The possibility of new things we can make it do tomorrow

Unwritten code has no value. The code that is being written today, if it will be creating value, leans towards helping with with a request/issue today or helping making/solving things easier tomorrow.

Then there's the various way of not creating value or favoring one of the two aboves. Either by taking on tech debt with hackish solutions or wasting time with YAGNI stuff.

If you haven't written any code, do you have infinite options?

So it's not about unwritten code, it's about the code that you're going to write and it's purpose. And the correct tradeoffs between resolving the ticket/todo and not shooting your future self's foot.

Writing code is commitment. And while the value for today is visible (either it's useful or it's not), the value for tomorrow is guesswork. But there's always some cost to be paid for later, so you guess in order to keep the cost minimal by anticipating what will be required.

skybrian3• 24 days ago

What corresponds to owning an option?

Scubabear684• 24 days ago

What Beck misses over and over again is there are many domains where there are “table stakes” that simply have to be done.

I think a huge amount of technical debt goes straight to YAGNI - devs pretending they are not going to need something that, yeah, they need.

YAGNI and related tenets were all excuses for “we are consultants in a field we don’t understand”.

fmbb3• 24 days ago

All tech debt I have ever seen in my 15 years of professional software development has been someone building too many abstractions or generalizations trying to future proof stuff.

zeroonetwothree• 24 days ago

That’s the opposite of the typical definition of tech debt.

Usually tech debt is debt—-ie something you take on to ship faster now at the expense of paying it in the long run.

cauch21• 24 days ago

I would say: if the feature is from a developer, high probability of YAGNI, if the feature is from a user, medium probability of YAGNI.

ajb2• 24 days ago

That's interesting, because it's not my experience. A lot of the technical debt I see is that someone half-assed something thinking it would be easy to improve later, but the layer violations and inadequate tests make doing so a massive project, once it's become load-bearing.

gofreddygo2• 24 days ago

we are consultants

This is the key insight. Design patterns were developed by a set of consultants. Promoted by other consultants. Consultants have perverse incentives, like bankers.

Realizing this made me critical of the design pattern kool aid. I've come to terms that these are going to be around longer than I'm going to be employed writing code. i keep the criticism to myself and avoid them when i dont see fit. Works ok.

As Hoare said:

    There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies and the other way is to make it so complicated that there are no obvious deficiencies.
  The first method is far more difficult.

actionfromafar2• 24 days ago

I still prefer the upsides of a shared vocabulary for talking about programming.

dang2• 24 days ago

"Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."

https://news.ycombinator.com/newsguidelines.html

cauch21• 24 days ago

I agree.

Nothing is all black or white of course, but I have personally observed situations where software engineers started with YAGNI and then said "that will require too much restructuring, we went into another direction, so, no, we cannot do it anymore". The worst part is that software engineers are not even in a good position to understand when YAGNI fails: when they don't plan for a useful feature, the solution is often for the users to just shrug it off and use a suboptimal solution rather than fighting and dying on a hill that they cannot win (at the end, the software developers can just say "nope, it's technically impossible" even if it was possible, they have a huge advantage). I also saw users just assuming there were good reasons why the feature did not exist ("well, I guess if they did not did it, it's technically impossible") and just don't even say it. And as the developers are not the users, they never notice anything.

100% with the way of illustrating: YAGNI is "we are consultants in a field we don't understand": sometimes, users are asking for too much, sometimes, they are asking for something reasoning, and the developers have no experience to distinguish between the two.

MoreQARespect4• 24 days ago

YAGNI is simply a tacit recognition that you can't predict the future with any reasonable level of certainty. The reason it is controversial is that some devs truly believe that they can predict the future with all the self assurance of a grandma sitting in front of a one armed bandit in vegas. So, they will:

* Create generalized functions where a specific one would have done.

* Create abstractions for something that will never be needed in the end.

* Create abstractions for something that will be needed but not in the form they initially expected.

It is not about avoiding refactoring. That misses the point entirely. Refactoring cleans up code mess that exists NOW - creating abstractions for somehting that exists NOW.

bazoom423• 24 days ago

YAGNI is not about things you know you need, because then you wouldn’t write any code ever.

Scubabear684• 24 days ago

This was the issue with the early agile-developed systems.

Not that they didn’t write no code, obviously, but they didn’t understand the domain and so YAGNI’d everyone to death. As a result there wasn’t enough code for the system would do what it needed to do.

The code was simple and highly testable, but didn’t actually do the job.

turlockmike• 24 days ago

My general principal is the cost of deleting code should be as low as possible and that includes the entire application as long as the data is around and easy to repurpose then the program itself should be as deletable as possible

passive• 24 days ago

(In general, I think we don't do enough to emphasize best practices in the era of AI, but...)

What Kent completely ignores here, as far a I can tell, is that there is significant value in finding out sooner what the needed features are. Building speculative structure can be a forcing function to establish requirements, because at least you start exposing failure modes. It might be more expensive than waiting, so hopefully you don't do it for most of your requirements, but sometimes it's your best option.

Building the wrong thing is now a much less expensive option, and that means the calculation around YAGNI is different. But it's still a calculation, and for now, each team needs to figure out how it has changed for them.

MoreQARespect4• 24 days ago

Building speculative structure can be a forcing function to establish requirements

Sure, if you're doing it as a spike but if you're not throwing the code away then it functions as a forcing function for creating slop.

skydhash22• 24 days ago

What Kent completely ignores here, as far a I can tell, is that there is significant value in finding out sooner what the needed features are.

But you're already know them, they come from your requirements and the design of the system that will fulfill those requirements. YAGNI is about creating something that is not part of the current requirements because you expect those requirements to change later. It's not about fleshing your current requirements and constraints (which mostly come with conversations with your stakeholders users/customer, your resources, and the engineering constraints and talents).

Creating prototypes only have value if you use them in your conversation with your stakeholders, building a project management model, or doing research for engineering purposes. Anything else is putting the cart before the horse.

gste2• 24 days ago

"When you build structure before the feature arrives, you’re committing on a guess."

I would argue that you are guessing either way. It could be probable that your feature will arrive, but not certain. It's a probability. If you don't build structure now, there's a cost for refactoring. If you build prematurely and the feature never arrives, you wasted effort.

What's the cost, probability and trade off between those possibilities? Obviously it depends. The whole YAGNI idea is a massive generalisation by design. Ultimately it depends on the circumstance.

Either way, it's often full of guessing and hand waving. It's the same problem as giving reliable work estimates. Certain software developers don't cope well with an uncertain world and look for black-and-white rules for everything.

dogwalker5000• 24 days ago

What's the cost, probability and trade off between those possibilities?

I read an old article that compared the various scenarios.

https://www.sebastiansylvan.com/post/the-perils-of-future-co...

TL;DR - it sides with YAGNI

AyanamiKaine• 24 days ago

I personally think it all comes to exploring and implementing solutions for problems. There is always a cost associated with solving the wrong problem. Or implementing a bad solution for something that was not even necessary.

Sometimes software developement can devolve to, just becoming a trial-error approach instead of thinking about a set of strategies/problems to explore.

There is a good case that exploring problems further in specific direction than needed can help long term. But implementing solutions aimlessly is never a good idea.

I think this is what Kent Beck really means, critizing implementing something just in case because you might need it in the future.

rwmj• 24 days ago

https://en.wikipedia.org/wiki/You_aren't_gonna_need_it in case anyone else was wondering

a96• 24 days ago

https://c2.com/xp/YouArentGonnaNeedIt.html on the original Wiki.

esafak• 24 days ago

This is terrible advice. You absolutely should structure your code with a view to the future. Easily refactorable code is synonymous with good code. And using the right abstractions makes this happen. Consult a domain expert to find out what you will need. This is what experience is for.

chuckadams2• 24 days ago

Yes, but you shouldn't structure for a future that isn't likely to actually happen. And if you keep things reasonably modular in general, it shouldn't be a major lift to refactor if that future does arrive. Still, Beck didn't do a very good job convincing me. And if you have to always explain what "Real" Blub is and how almost no one practices Real Blub, then maybe Blub was just never a good maxim to begin with.

mrkeen2• 24 days ago

And if you have to always explain what "Real" Blub is and how almost no one practices Real Blub, then maybe Blub was just never a good maxim to begin with.

I'll push back.

No-one I work with seems to practice "real DI", "real encapsulation", or "real agile", and the software is the worse for it.

mrkeen2• 24 days ago

At some point for me something flipped.

I YAGNI the concretion and write the abstract-as-possible version.

Do I write a UserStore? That would be the simplest, right? Well no, I might not need that particular formulation of a User. So I just make a Store of anything-which-is-storable.

If you're not used to it, it looks like you've over-engineered and ended up with Generics soup, but paradoxically, you're committing yourself the least to any concrete implementation.

dpark3• 24 days ago

If you're not used to it, it looks like you've over-engineered and ended up with Generics soup

Yes, it looks exactly like that. You’ve built not just an interface for UserStore you probably didn’t need, but a generalized Store abstraction that you definitely didn’t need.

but paradoxically, you're committing yourself the least to any concrete implementation

This isn’t paradoxical at all. You’ve avoided committing yourself to a concrete implementation by implementing layers of goop you don’t need and likely never will. And because you did all this abstraction without real needs to ground it, you almost certainly did it wrong even if you do eventually need it.

You are gonna need a user store, so you should have built that first.

tpoacher• 22 days ago

Then again, this goes completely against the "O" in the SOLID principles (and possibly also the "D" too).

Personally I prefer SOLID to YAGNI.

antonvs2• 24 days ago

Chet, eyes going up to the ceiling, pausing, “Oh.” Walks away.

That's the first step in routing around damage. In this case, Kent Beck is the damage, not being willing to listen to what a teammate has to say about the design of a system.

zamalek• 23 days ago

I recently had to functionally migrate away from a codebase that had a ton of YAGNI. _Even with_ an agent it was a herculean task: how do you know if something is really used in a distributed system. I missed things, the agent missed things, it all took way longer than it should have.

(FWIW, I wasn't simply doing a 1:1 port, I took the opportunity to simplify - which meant completely understanding how the old system worked, including things that were _never_ used if I failed to identify them as such)

The cost YAGNI was never about

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