AI changes the economics of software rewrites • Hacker News Board

Re: AI changes the economics of software rewrites

#41

Post by CraigJPerry » Thu, Jul 09, 2026, 7:35 AM UTC

nomel wrote: post #37

matsemann wrote: post #20

What's the point of the rewrite if it doesn't fix the underlying issues, though? A rewrite being a good idea often hinges on the ability to simplify. After a decade or more, it's now apparent what the application should and shouldn't do, so one can build it with those learnings and shed all tech debt from how it grew organically. Aka preserving all behavior is not what I would want from a rewrite. The point would be…

Say I rewrite a large codebase from python to C++, preserving all behavior. That's up to a 50x speed up.

Not a good example i'd say given Python's position as pretty much the ultimate glue language :) You'd more likely keep the python shell (and faster developer iteration speed) and push measured hotspots down into c++/rust/c/whatever.

Incidentally, Whenever i've done this in the past it's had a pleasant side effect of improving architecture. You end up forcing something akin to "push for's down and pull if's up" because crossing the ffi boundary is not free. It can be quite magical, as in leading to comically unbelievably speed ups when you also take advantage of vector intrinsics.

Re: AI changes the economics of software rewrites

#42

Post by rapidaneurism » Thu, Jul 09, 2026, 7:36 AM UTC

fxtentacle wrote: post #25

akssri wrote: post #21

Au contraire - LLMs are quite bad at large scale pattern fidelity. They'll even forget key details and constraints unless told over and over again. That's why AI-written code has the quality of a patch-on-patch-on-patch.

Fully agree. I tried to refactor parts of a large code base with Fable+ultracode and it just keeps accidentally merging distinct concepts and making up explanations/reasonings that the code base did not contain. For example, the code base contains a physical controller. It’s closed loop in that it can react in realtime to changes. But it’s a slightly untypical implementation because this one can even look into the fu…

Would putting that in black and white in the comments around then controller help?

Re: AI changes the economics of software rewrites

#43

Post by gofreddygo » Thu, Jul 09, 2026, 7:36 AM UTC

akssri wrote: post #21

Au contraire - LLMs are quite bad at large scale pattern fidelity. They'll even forget key details and constraints unless told over and over again. That's why AI-written code has the quality of a patch-on-patch-on-patch.

[dead]

Re: AI changes the economics of software rewrites

#44

Post by AndrewThrowaway » Thu, Jul 09, 2026, 7:37 AM UTC

al_borland wrote: post #38

AndrewThrowaway wrote: post #32

Earlier quoted context omitted.

If you gave some junior dev a large codebase and just told to "refactor it" you would get a terrible result. If you gave junior dev exact tasks what to do where you will get better results. Just like with LLM.

That’s why junior devs generally aren’t give the responsibility of architecting a large scale refactor. Yet people seem to be trying to had these types of tasks over to LLMs.

Exactly. Is it LLMs fault or yours to believing in it so much.

Re: AI changes the economics of software rewrites

#45

Post by SunlightEdge » Thu, Jul 09, 2026, 7:41 AM UTC

In my experience, LLM's can be both impressive and also totally wrong in their reasoning when doing a code re-write. I was involved in an api migration a while back and while at times the llms were able to re-write the code - they also had instances where their totally misunderstood the platform and their recommendations for solving the issue was almost dangerously wrong. an over reliance on them can also make people lazy at what are quite simple programming issues (but they can code things up a hell of a lot faster) - its a tool and the outputs need to be carefully reviewed (with a dose of critique when its an uncertain area).

Re: AI changes the economics of software rewrites

#46

Post by trollbridge » Thu, Jul 09, 2026, 7:44 AM UTC

Semaphor wrote: post #29

matsemann wrote: post #20

What's the point of the rewrite if it doesn't fix the underlying issues, though? A rewrite being a good idea often hinges on the ability to simplify. After a decade or more, it's now apparent what the application should and shouldn't do, so one can build it with those learnings and shed all tech debt from how it grew organically. Aka preserving all behavior is not what I would want from a rewrite. The point would be…

I work on a codebase from the early 2000s, a lot of it using webforms, a long abandoned .NET technology. A rewrite preserving all behavior and making no observable changes whatsoever would be amazing. But it’s also tested exactly as well as you’d expect from something like that so I’d rather not let AI go wild.

LLMs/agents are a great way to create a test harness for something like that.

Re: AI changes the economics of software rewrites

#47

Post by LtWorf » Thu, Jul 09, 2026, 7:44 AM UTC

AndrewThrowaway wrote: post #44

al_borland wrote: post #38

Earlier quoted context omitted.

That’s why junior devs generally aren’t give the responsibility of architecting a large scale refactor. Yet people seem to be trying to had these types of tasks over to LLMs.

Exactly. Is it LLMs fault or yours to believing in it so much.

"Coding is solved"

Re: AI changes the economics of software rewrites

#48

Post by trollbridge » Thu, Jul 09, 2026, 7:46 AM UTC

retinaros wrote: post #33

First three paragraphs and I can tell its opus 4.8

You are a man of taste and refinement; I could tell it was an LLM, but didn't recognise it was Opus and certainly had no idea which version.

(At least the author sprang for a $20 a month subscription.)

Re: AI changes the economics of software rewrites

#49

Post by apsurd » Thu, Jul 09, 2026, 7:50 AM UTC

jdw64 wrote: post #17

The point where I truly feel that AI is a game changer is that these kinds of posts keep appearing. Tautological outcries keep going on both sides, pro and con, endlessly repeating circular logic. There's no real substance or evidence, and rather than discussing how things were actually applied, it's just an echo chamber for whatever group you belong to. In that sense, my homepage ( https://www.makonea.com/en-US ) do…

this post is no good. It's a continual rehash of what's going on in the industry. That's how all social media is, it's entirely time sensitive, keep saying the the same things and be the one to say it so the discussion happens on your "content".

OP is playing the game. The post literally says "from LinkedIn" so if you look, he has 500+ connections and 1400 followers. That's not nothing. Good for him, all advice points to this new attention economy we live in.

I'm a bit aged out of all this. And I rode the 2010s wave so I can't give any advice in good conscience. I can only say that I see you and there's a whole world of silent majorities out there with no follow count and no broetry with our name on it. (search for that word in this thread, just learned it, it's great!)

Re: AI changes the economics of software rewrites

#50

Post by al_borland » Thu, Jul 09, 2026, 7:50 AM UTC

AndrewThrowaway wrote: post #44

al_borland wrote: post #38

Earlier quoted context omitted.

That’s why junior devs generally aren’t give the responsibility of architecting a large scale refactor. Yet people seem to be trying to had these types of tasks over to LLMs.

Exactly. Is it LLMs fault or yours to believing in it so much.

It is the fault of the salesmen and evangelists.

I’ve been hearing for quite some time now that I should be using an LLM to plan before the build. This is treating the LLM as the architect, not as a junior being handed small tasks here and there.

I haven’t bought into it, so don’t use it this way, but an army of people online and in the media are pushing the fomo hard and telling people this is how it should be used. If the LLM isn’t doing what we want, it simply means we need to use the LLM even more. That’s the prevailing message from the industry.