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AI code is legacy code?
- OnlyMortal 1y agoAll code is legacy. Business needs shift. The likes of Copilot are ok at boiler-plate if it has an example or two to follow. It’s utterly useless at solving problems though.
- andrewflnr 1y ago> All code is legacy. No. Plainly incorrect by any reasonable definition (hint: it's in the memory of the people working on it! As described in OP!), and would immediately render itself meaningless if it were true.
- OnlyMortal 1y agoYou’re quite clearly wrong. You write code to fit the immediate business need and that shifts rapidly over a year or two. If you do otherwise, you’re wasting your time and the money of the enterprise you work for. You cannot see the future however smart you might be.
- mediaman 1y agoWhy are enterprises running code from 1985? How long code needs to last is actually highly variable, and categorical absolutist statements like this tend to generally be wrong and are specifically wrong here. Some code will need to change in a year. Some will need to last for forty years. Sometimes it's hard to know which is which at the time it is written, but that's part the job of technical leadership: to calibrate effort to the longevity of the expected problem and the risks of getting it wrong.
- andrewflnr 1y agoYou would start to have a case if you said "all code older than a year or two". You didn't, you just said "all", including code you wrote last week or five minutes ago. More to the point, you're including well-factored code that you know well and are used to working with day in and day out. If that's legacy code, then you've triggered the second half of my objection.
- saulpw 1y ago"Rapidly over a year or two" That time window is when the code is not legacy yet. When the developers who wrote the code are still working on the code, the code is loaded into their collective brain cache, and the "business needs" haven't shifted so much that their code architecture and model are burdensome. It's pithy to say "all code is legacy" but it's not true. Or, as from the other reply, if you take the definition to that extreme, it makes the term meaningless and you might as well not even bother talking, because your words are legacy the instant you say them.
- perrygeo 1y agoObviously, code is constantly changing. That's not really the point. The point is that as soon as no one understands the code (thus no one on staff to effectively debug or change it) it's "legacy" code. Let's say you need to make big sweeping changes to a system. There's a big difference if the company has the authors still happily on staff vs. a company that relies on a tangle of code that no one understands (the authors fired 3 layoffs ago). Guess which one has the ability to "shift rapidly"?
- surfingdino 1y agoAny code becomes legacy code as soon as it goes into production. The only non-legacy code is the one you delete right after writing it.
- andrewflnr 1y agoBy what definition? You might be more reluctant to change it now, but that's not the same thing.
- manojlds 1y agoEvery code is.
- wetpaws 1y ago[dead]
- lacker 1y agoIt's tough to generalize about "AI code", there's a huge difference between "please make a web frontend to this database that displays table X with some ability to filter it" and "please refactor this file so that instead of using plain strings, it uses the i18n api in this other file".
- havkom 1y agoWhat is the difference between them? Both seems like quite trivial implementations?
- elliotec 1y agoYeah these are both extremely basic great use cases for LLM-assisted programming. There’s no difference, I wonder what the OP thinks that is.
- klabb3 1y agoDisagree. There is almost no decision making in converting to use i18n APIs that already have example use cases elsewhere. Building a frontend involves many decisions, such as picking a language, build system, dependencies, etc. I’m sure the LLM would finish the task, but it could make many suboptimal decisions along the way. In my experience it also does make very different decisions from what I would have made.
- int_19h 1y agoThe AI will pick the most common technologies used for this purpose, which is both "good enough" and also what people generally do at scale (for this exact reason).
- klabb3 1y agoThis was the promise of no-code. ”All apps are crud anyway”, ”just build for common use cases” etc. This didn’t turn out to be true as often as predicted. If averaging people’s previous decisions was truly a fruitful way, we’d have seen much stronger results of that before AI.
- BSOhealth 1y agoCurrent state is temporary. What’s coming next is organic, living code. Think less testing, more self-healing. Digital code microphages. Soon our excitement over CICD and shipping every minute will look very naive. There’s a future coming where every request execution could be through a different effective code path/base.
- selfselfgo 1y ago[dead]
- Swizec 1y ago> There’s a future coming where every request execution could be through a different effective code path/base. Every CISO and legal department just had a heart attack. And every cryptobro went: “See! Big big market” (for paying ransoms) But hey us nerds always said code shouldn’t be copyrightable and had no IP value. Maybe that will finally come true! Punk: 1, corporate: 0
- peteforde 1y agoOkay, I'll bite: the comparison to smart contracts is a less-than-helpful lens because the people who deploy them are perversely incentivized to optimize out things like boundary checks and other error handling to minimize how much they cost to publish. AI generated code might well come with its own constraints and baggage, but the whole "every byte is lost profit" thing is a fundamental and IMO damning aspect of crypto code.
- Swizec 1y ago> the comparison to smart contracts is a less-than-helpful lens Oh no that’s not what I meant. Sorry too much snark. I was trying to say that on-demand-AI-figures-out-whatever will be so eminently hackable/brickable that companies will need to pay out ransoms on the weekly. These days those ransoms are usually crypto.
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- colesantiago 1y agoWe are going to get more of it anyway. Plenty of new jobs from AI because of AI code, vibe coding.
- TZubiri 1y ago"AI is “stateless” in an important way, even with its context windows. It can infer why something may have been written in a particular way, but it (currently) does not have access to the actual/point-in-time reasoning the way an actual engineer/maintainer would." CoT fixes this. And in a way, non CoT can retrigger its context by reading the code. In a similar fashion, engineers remember their context when reading code, not necessarily by keeping it all in their head
- nikanj 1y agoI believe one of the biggest growth steps on the path from junior intern to senior fellow is recognizing that code does not rot, and refactoring code biweekly because someone thought of yet another way to organize it brings zero business value. "That code is old and the paradigms are dated" is uttered with the same disdain as "That shed is old and the floorboards have dry rot" The best thing that happens to a startup is actual traction and paying customers, because once that happens the refactoring churn is usually shoved to the back burner
- codr7 1y agoThe understanding of the code certainly degrades, which means any updates cause the code to lose its integrity over time.
- nikanj 1y agoThe older code is, the more people probably have at least a passing understanding of it - just by virtue of osmosis and accidental exposure. A thorough rewrite means only the person who wrote is is familiar with it. Of course you can start a code review policy and make sure everyone at the dev team has gone through all of the code that gets written, but that becomes a ludicrous bottleneck when the team grows
- codr7 1y agoOnce the code is mature and only needs sporadic updates, that's not true anymore from my experience. The story around the code is lost, people leave and the developers who make changes weren't around when the code was first written.
- kachapopopow 1y agoForget AI "code", every single request will be processed BY AI! People aren't thinking far enough, why bother with programming at all when an AI can just do it? It's very narrow to think that we will even need these 'programmed' applications in the future. Who needs operating systems and all that when all of it can just be AI. In the future we don't even need hardware specifications since we can just train the AI to figure it out! Just plug inputs and outputs from a central motherboard to a memory slot. Actually forget all that, it'll just be a magic box that takes any kind of input and spits out an output that you want! -- Side note: It would be really interesting to see a website that generates all the pages every time a user requests them, every time you navigate back it would look the same, but some buttons in different places, the live chat is in a different corner, the settings now have a vertical sidebar instead of a horizontal menu.
- codybontecou 1y agoA digital Costco.
- TeMPOraL 1y agoOr Star Trek, if you take a positive perspective instead of cynical one.
- jsheard 1y ago> Side note: It would be really interesting to see a website that generates all the pages every time a user requests them, every time you navigate back it would look the same, but some buttons in different places, the live chat is in a different corner, the settings now have a vertical sidebar instead of a horizontal menu. Please don't give A/B testers ideas, they would do that 100% unironically given the chance.
- wheelie_boy 1y agoIt's like that AI doom, where when you look at the floor and back up you're in a totally different room
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- closewith 1y agoLegacy code is invariably the highest earning code for any business, so this is not the angle you want to take with management if your intention is to dissuade them from AI coding tools.
- deleted 1y ago[deleted]
- fc417fc802 1y agoAll the downsides of legacy without the upside of having been selected for by the market.
- rufius 1y agoAll code is legacy code from day one.
- hollerith 1y agoAll this legacy code is going to be hell on the AIs that will have to maintain it in the future
- codr7 1y agoThey don't have to do anything. When society crumbles because nothing works anymore its going to be our problem.
- peteforde 1y agoMy hot take is that using Cursor is a lot like recreational drugs. It's the responsibility of the coder/user/collaborator to interact with the code and suggestions any model produces in a mindful and rigorous way. Not only should you have a pretty coherent expectation of what the model will produce, you should also learn to default/assume that each round of suggestions is in fact not going to be accepted before it is. At the very least, be prepared to ask follow-up questions and never blindly accept changes (the coding equivalent of drunk driving). With Cursor and the like, the code being changed on a snippet basis instead of wholesale rewriting that is detached from your codebase means that you have the opportunity to rework and reread until you are on the same page. Given that it will mimic your existing style and can happily explain things back to you in six months/years, I suspect that much like self-driving cars there is a strong argument to be made that the code it's producing will on average be better than what a human would produce. It'll certainly be at least as consistent. It might seem like a stretch to compare it to taking drugs, but I find that it's a helpful metaphor. The attitude and expectations that you bring to the table matter a lot in terms of how things play out. Some people will get too messed up and submit legal arguments containing imaginary case law. In my case, I very much hope that I am so much better in a year that I look back on today's efforts with a bit of artistic embarrassment. It doesn't change the fact that I'm writing the best code I can today. IMO the best use of LLMs in coding is to help people who already know how to code rapidly get up to speed in domains that they don't know anything about. For me, that's been embedded development. I could see similar dynamics playing out in audio processing or shader development. Anything that gets you over that first few hard walls is a win, and I'll fight to defend that position. As an aside, I find it interesting that there hasn't been more comparison between the hype around pair programming and what is apparently being called vibe coding. I find evidence that one is good and one is bad to be very thin.
- gregwebs 1y agoOne definition of legacy code I have seen is code without tests. I don't fully agree with that, but it is likely that your untested code is going to become legacy code quickly. Everyone should be asking AI to write lots of tests- to me that's what AI is best at. Similarly you can ask it to make plans for changes and write documentation. Ensuring that high quality code is being created is where we really need to spend our effort, but its easier when AI can crank out tests quickly.
- dang 1y agoMy favorite definition of "legacy code" is "code that works". Anybody know where that quip originated? (ChatGPT tells me Brian Kernighan - I doubt it. That seems like LLM-enabled quote hopping - https://news.ycombinator.com/item?id=9690517 https://news.ycombinator.com/item?id=9690517)
- turtleyacht 1y agoAfter hearing legacy code defined as "code that runs in production," it reset my perception around value and thoughtful maintenance. Cannot find the reference, though.
- nonethewiser 1y ago"Legacy code" is such a loaded term. There is definitely large intersection between people's working definition of "legacy code" and "code that works". At the same time this is usually NOT what people intend to include. But it fits their definition nonetheless. Take the author's definition: >When something is older, and someone else built it That usually describes the most important, core part of any system that has existed for any significant amount of time. It may even be well understood by most people.
- nicce 1y agoI would say that legacy code is something that one does not simply change. You cannot update any dependencies because then everything breaks. You cannot even easily add new features because it is difficult to even run the old dependencies your code is using. With LLMs, creating legacy code is using some old APIs, old patterns to do something, that is not relevant anymore, but the LLM does not know about. E.g. if you ask any LLM to use Tailwind CSS, they use V3 no matter what you try to do while the V4 is the latest. LLMs try to tell you that pure CSS configuration is wrong and you should use the .js config.
- DevKoala 1y agoI’ve been very successful with AI generated code. I provide the requirements and design the system architecture, and AI generates the code I would usually delegate. If any specific part requires me to dig in, I do it myself. PS: Also, some people act as if they have to remove their common sense when using Gen AI code. You have to review and test the generated code before merging it.
- mrweasel 1y agoMy old boss and I used to defend ourselves to younger colleagues with the argument that "This is how you did it back in the day". Mostly it was a joke, to "cover up" our screw-ups and "back in the day" could be two weeks ago. Still, for some things we weren't wrong, our weird hacks where do to crazy edge cases or integrations into systems designed in a different era. But we where around to help assess if the code could be yanked or at least attempt to be yanked. LLM assisted coding could technically be better for technical debt, assuming that you store the prompts along side the code. Letting someone what prompt generated a piece of code could be really helpful. Imagine having "ensure to handle the edge case where the client is running AIX 6". That answers a lot of questions and while you still don't know who was running AIX, you can now start investigating if this is still needed.
- mplanchard 1y ago> ensure to handle the edge case where the client is running AIX 6 Regardless if the source was AI or not, this should just be a comment in the code, shouldn’t it? This is exactly the sort of thing I would ask for in code review, so that future authors understand why some weird code or optimization exists.
- mrweasel 1y agoIt should, but I think most of us read enough old code to know that this doesn't happen as often as we'd like. With an LLM you already wrote the prompt, so if you had an easy way to attach the prompt to the code it could make it more likely that some form of documentation exists. Some times you also fail to write the comment because at the time everyone knew why you did it like that, because that's what everyone did. Now it's 10 years later and everyone doesn't know that. The LLM prompt could still require you to type out the edge case that everyone in your line of business knows about, but might not a generalised across the entirety of the software industry.
- mplanchard 1y agoI'm always a fan of more historical context on code, so maybe it'd be an okay fallback for a proper comment and git blame, but you'd have to find a way to separate the meaningful part of the prompt from the preamble that is implicitly inserted into most prompts ("you are a helpful assistant, only output code, no formatting markers, etc etc"). That said, I suspect it wouldn't actually be that useful for the "why" very often, which is usually what's lacking in these cases. I would guess that far more people prompt the LLMs with the "how," e.g. "write a function that takes these things as input and produces this output," which of course we can just read in the code.
- dang 1y agoThe opening of the article derives from (or at least relates to) Peter Naur's classic 1985 essay "Programming as Theory Building". (That's Naur of Algol and BNF btw.) Naur argued that complex software is a shared mental construct that lives in the minds of the people who originally build it. Source code and documentation are lossy representations of the program—lossy because the real program (the 'theory' behind the code) can never be fully reconstructed from them. Legacy code here would mean code where you still have the artifacts (source code and documentation), but have lost the theory, because the original builders have left the team. That means you've lost access to the original program, and can only make patchwork changes to the software rather than "deep improvements" (to quote the OP). Naur gives some vivid examples of this in his essay. What this means in the context of LLMs seems to me an open question. In Naur's terms, do LLMs necessarily lack the theory of a program? It seems to me there are other possibilities: * LLMs may already have something like a 'theory' when generating code, even if it isn't obvious to us * perhaps LLMs can build such a theory from existing codebases, or will be able to in the future * perhaps LLMs don't need such a theory in the way that human teams do * if a program is AI-generated, then maybe the AI has the theory and we don't! * or maybe there is still a theory, in Naur's sense, shared by the people who write the prompts, not the code. There was an interesting recent article and thread about this: Naur's "Programming as Theory Building" and LLMs replacing human programmers - https://news.ycombinator.com/item?id=43818169 https://news.ycombinator.com/item?id=43818169 - April 2025 (129 comments)
- krrishd 1y agoTIL / unconscious reference on my part, super interesting! Link for the curious: https://pages.cs.wisc.edu/~remzi/Naur.pdf https://pages.cs.wisc.edu/~remzi/Naur.pdf
- dang 1y agoWith lots of HN threads over the years! Naur's "Programming as Theory Building" and LLMs replacing human programmers - https://news.ycombinator.com/item?id=43818169 https://news.ycombinator.com/item?id=43818169 - April 2025 (129 comments) Programming as Theory Building (1985) [pdf] - https://news.ycombinator.com/item?id=42592543 https://news.ycombinator.com/item?id=42592543 - Jan 2025 (44 comments) Programming as Theory Building (1985) - https://news.ycombinator.com/item?id=38907366 https://news.ycombinator.com/item?id=38907366 - Jan 2024 (12 comments) Programming as Theory Building (1985) [pdf] - https://news.ycombinator.com/item?id=37263121 https://news.ycombinator.com/item?id=37263121 - Aug 2023 (36 comments) Programming as Theory Building (1985) [pdf] - https://news.ycombinator.com/item?id=33659795 https://news.ycombinator.com/item?id=33659795 - Nov 2022 (1 comment) Naur on Programming as Theory Building (1985) [pdf] - https://news.ycombinator.com/item?id=31500174 https://news.ycombinator.com/item?id=31500174 - May 2022 (4 comments) Naur on Programming as Theory Building (1985) [pdf] - https://news.ycombinator.com/item?id=30861573 https://news.ycombinator.com/item?id=30861573 - March 2022 (3 comments) Programming as Theory Building (1985) - https://news.ycombinator.com/item?id=23375193 https://news.ycombinator.com/item?id=23375193 - June 2020 (35 comments) Programming as Theory Building (1985) [pdf] - https://news.ycombinator.com/item?id=20736145 https://news.ycombinator.com/item?id=20736145 - Aug 2019 (11 comments) Peter Naur – Programming as Theory Building (1985) [pdf] - https://news.ycombinator.com/item?id=10833278 https://news.ycombinator.com/item?id=10833278 - Jan 2016 (15 comments) Naur’s “Programming as Theory Building” (2011) - https://news.ycombinator.com/item?id=7491661 https://news.ycombinator.com/item?id=7491661 - March 2014 (14 comments) Programming as Theory Building (by Naur of BNF) - https://news.ycombinator.com/item?id=121291 https://news.ycombinator.com/item?id=121291 - Feb 2008 (2 comments)
- nialv7 1y ago> It can infer why something may have been written in a particular way, but it (currently) does not have access to the actual/point-in-time reasoning the way an actual engineer/maintainer would. Is that really true? A human programmer has hidden states, i.e. what is going on in their head cannot be fully recovered by just looking at the output. And that's why "Software evolves more rapidly under the maintenance of its original creator, and in proportion to how recently it was written", as is astutely observed by the author. But transformer based LLMs do not have this hidden state. If you retain the text log of your conservation with an LLM, you can reproduce its inner layer outputs exactly. In that regard, an LLM is actually much better than humans.
- Retr0id 1y agoThe internal state and accompanying transcripts of an LLM isn't really comparable to the internal state of a human developer.
- vips7L 1y agoAll code is legacy code.
- exiguus 1y ago[flagged]
- exiguus 1y agoBtw, this comment was created by AI. Now in short: Static code analysis, aka your linter, is your friend; if it's not in place to catch human errors, the problem will only worsen with AI-generated code. And this is only half the truth, as AI will add another level of stupidity that your current linter can't detect yet. And for now, i will not start with non-functional or business requirements.
- ozim 1y agoEvery piece of code is legacy code a week later. Real issue is that AI code is not your code in terms of copyrights so if you want to run a company on that code and someone makes a copy you don't even have grounds to argue.
- j45 1y agoMost if not all code will be legacy code, if it gets to live long enough.