22 ms·

Things You Should Never Do (2000)

128 points by HugoDias 6y ago

larsenwolf 6y ago
There are methods for rewriting legacy systems. Articles like this make the job of improving systems more difficult by creating an impassable set of presuppositions among non-technical stakeholders.
dharmab 6y ago
I have successfully rewritten a major codebase. It took about two years to implement. It helped that it involved moving from a mostly proprietary stack to a mostly FOSS stack, which allowed us to leverage the community and spent more time on business features rather than plumbing.
542458 6y ago
I think saying "you should never rewrite code from scratch" is a bit too dogmatic. There's a cost and risk tradeoff. I think people underestimate the cost of a rewrite (Due to ego or NIH or yak shaving), but I don't think it's never the answer. Sometimes the language is so old it's cripplingly expensive to hire programmers in. Sometimes the code is deeply tied to a hardware architecture that is extinct. Sometimes the legacy code actually is that bad. For reference, I've done total rewrites on two different small-ish software projects - in both cases because the original author had made design choices that made the whole thing unsustainable in the long run (no blame implied, it's more about shifting goals). For reference, Twitter has done a total rewrite of their large codebase, and lived to tell the tale.
- m12k 6y ago
  Yeah, it's probably closer to things like fiddling with assembly, manual thread syncing and rolling your own crypto - it's not that you should never do it, but unless you're very, very sure what you're doing and why, it's probably a bad idea.
- wisemanwillhear 6y ago
  Indeed. The most successful project I've work in my career was a re-write of a very large internal tool. The choice to "re-write" & re-envision was almost universally regarded as a good choice after the fact. One of the biggest reasons cited was moving to a different tech stack.
- shoes_for_thee 6y ago
  I hear you. But I think that dogmatically saying "You should never rewrite code from scratch" is just useful enough to catch the vast majority of instances when you should not rewrite code from scratch. I'm willing to be called out for being totally wrong for my dogma in the rare instance that the application should be rewritten from scratch. Every project I have ever joined on, there has been someone who wants to start fresh. There have been a lot of projects. There was one such instance where it was a good idea.
projektfu 6y ago
Always important to mention the alternative, a "Strangler Fig Application", also known as the strangler pattern. https://martinfowler.com/bliki/StranglerFigApplication.html https://martinfowler.com/bliki/StranglerFigApplication.html
mjw1007 6y ago
« It’s important to remember that when you start from scratch there is absolutely no reason to believe that you are going to do a better job than you did the first time » With the benefit of twenty years of hindsight, I think the programmers who performed the rewrite in question did a better job than the original Netscape implementation. Come to think of it, I'm typing this message on the direct descendent of that rewrite, while the competitor to whom they gave « a gift of two or three years » has been forced to abandon their codebase in favour of a third-party one.
- tedunangst 6y ago
  Firefox has less market share today than Netscape did at the time this was written.
  - myth2018 6y ago
    There is a few more competitors today, though.
  - larsenwolf 6y ago
    An anecdote I know, but I recently converted from Chrome to Firefox and am actively distancing all of our technology within away from Google.
  - sukilot 6y ago
    But the market share was lost to a "rewrite" by a competitor.
S_A_P 6y ago
Never say never, but still a lot of truth to this. I generally think refactoring is the better way to go unless you are backed into an architectural corner. Say, for instance the app was built in power builder and needs to support 64 bit OS. That’s a rewrite in a new language. Say the app was a MacOS 9 and OSX is coming. Rewrite. Otherwise it’s probably better to refactor old code than to chase green fields.
bachmeier 6y ago
Relevant links: https://medium.com/@herbcaudill/lessons-from-6-software-rewrite-stories-635e4c8f7c22 https://medium.com/@herbcaudill/lessons-from-6-software-rewr... And this DHH talk (transcript) https://businessofsoftware.org/2015/10/david-heinemeier-hansson-rewrite-basecamp-business-of-software-conference-video-dhh-bos2015/ https://businessofsoftware.org/2015/10/david-heinemeier-hans...
hn_throwaway_99 6y ago
I'm a big fan of Joel Spolsky's earlier blog posts, but to be honest, I don't think this piece has aged well. If anything, I'm more of the opinion now that you should almost always plan to do a rewrite, eventually. Lots of big companies successfully rewrite stuff all the time. Google is fairly well known for having rewritten large, critical pieces of their codebase over the years. If anything, what should be warned against is big bangs. Netscape's problem isn't that they did a rewrite (which eventually became Firefox, mind you) it's that they essentially abandoned their old code too early, and similarly, they also announced the rewrite too soon. If you're going to do a rewrite, do it quietly, and don't announce it until it's close to ready, and even then you can roll out slowly. For example, the infamous Digg v4 debacle is another example, but the problem isn't that they did a rewrite, it's that they did a rewrite to produce a product nobody wanted, and they burned any possibility of going back after they released it.
- MarkSweep 6y ago
  Netscape’s big bang rewrite is in great contrast to the current work on Firefox Quantum. Mozilla is slowly rewriting pieces of the browser in Rust to gain better performance and security.
  - michaelcampbell 6y ago
    The reason is less important than the methods.
    - the-dude 6y ago
      I can't imagine this to be true.
- goto11 6y ago
  The more experience I get, the more I think Joel was right. Developers want to believe rewrite-from-scratch can succeed because green-field development is easier and more fun than slowly refactoring inscrutable legacy code. But long before the rewrite project achieve feature parity with the original, it is already marred by the same issues that motivated the rewrite. Because the dysfunction which led to the original code turning into a mess have not been addressed. "But we are smarter than those other guys who wrote this mess" - if that is the case, you should be smart enough to fix the mess.
mojuba 6y ago
I once rewrote a monstrous app that was in development for 5 years (!), in just one month. In terms of LOC it was 20 times smaller than the old codebase. Had the same functionality and then some more. It had zero bugs in the first release, compared to myriad of bugs in the previous one (mostly multithreading related - yes it's hard). All I did was, I dumped Microsoft's COM/DCOM and replaced it with REST; also replaced C++ and VB with C#. Totally made sense to rewrite from scratch and it was a big win with absolutely no downsides. Like, no downsides whatsoever because otheriwse the same month I would have spent fixing maybe 4 or 5 multithreading bugs in the old codebase. Anyway, never say "never do X" because you are most likely wrong.
- mamcx 6y ago
  This is my experience too. I rewrite often and liberally, and even switch langs (on the side) to check if it can bring huge gains.
- gfodor 6y ago
  I think this advice is not relevant if you are on a project where it's feasible for a single developer to re-write it in a month. Burning a month on a failed re-write is certainly worth the risk if you take a run at it. For projects where there are several devs going to be working on the re-write for a long time, it almost certainly is a sign that the 'legacy' code has way more knowledge embedded in it than it might seem. Having been on the death march of a re-write before I think the signs are usually obvious when you're in one scenario or the other.
  - perl4ever 6y ago
    >I think this advice is not relevant if you are on a project where it's feasible for a single developer to re-write it in a month The implication is that is can be non-obvious if something is potentially that sort of project, as it originally was a large undertaking. I mean, you can assume it's a fake story, but they said it wasn't originally a one person, one month thing. I don't know that it implies the person who rewrites something is a super-genius, it's just that sometimes a new perspective or tools allow a really amazing improvement.
dang 6y ago
From the three dozen or so previous submissions, the actual discussions seem to be: 2013 https://news.ycombinator.com/item?id=6327021 https://news.ycombinator.com/item?id=6327021 2012 https://news.ycombinator.com/item?id=3624830 https://news.ycombinator.com/item?id=3624830 2012 (a bit) https://news.ycombinator.com/item?id=3449953 https://news.ycombinator.com/item?id=3449953 2009 https://news.ycombinator.com/item?id=608431 https://news.ycombinator.com/item?id=608431
winrid 6y ago
A better way to put it IMO is that you should never go dark on your customers during a rewrite.
almostdeadguy 6y ago
Currently on a project where I find myself thinking a lot about this post. I think a lot of the comments here are missing some of the finer points of this argument. "Rewriting" is not per se the problem, "rewriting from scratch" where a project is effectively put on hold until the rewrite gets done, is the real quagmire. There are legitimate ways of doing a rewrite that don't require boiling the ocean and prevent you from shipping. And I'm sure there are exceptions as well, but as a general piece of advice about software engineering I've found this to have a better shelf life than many other nuggets of advice.
dlbucci 6y ago
I completely agree! Throwing away your code and starting over is failing to atone for the sins of the past, and I feel like it prevents you from learning or growing as a programmer. That's why I don't think I'll ever rewrite something from scratch again. To me, this was nowhere more obvious than from my old co-worker who was constantly trying to rewrite the internal site we worked on. First it was angular and coffeescript, but that was apparently unmaintainable after 3 months (!!!). So they rewrote it and then I joined, and it apparently made it to 6 months. Then we tried to rewrite it in TypeScript and React which blew 10 man weeks away before we abandoned it. And then he tried to do TypeScript and Angular again but it never launched. Meanwhile, after the React debacle, I learned my lesson and focused on rewriting and rearchitecting the old code to follow more modern Angular practices (1.5 components and such), and suddenly the code didn't seem so unworkable anymore! Quality improved and features were added that made it a very popular internal site, still in use 3 years after I left that team. So I agree, I think you should always try to improve what you have instead of starting over. (If only our UX designers would go for incremental improvements too...)
- rubber_duck 6y ago
  Rewriting anything complex and actively used from scratch is not a good idea and the problems have been hashed out may times. Having said that, angularjs and coffescript is a terrible software stack in a dead ecosystem, the best course of action is probably incremental rewrite - React is really good at that because it starts out as a small rendering library and you can incrementally replace stuff like routing etc.
  - dlbucci 6y ago
    I completely agree. On my next app, I was forced to use AngularJS (in 2017, somehow), but did get to use TypeScript (which is somewhat hobbled by having to use Angular templates), and this is exactly what we're doing now: rewriting components one-by-one in React. I love refactoring and React is much nicer, so I'm having fun with it :)
  - buu700 6y ago
    For that example, I would just use Decaffeinate to migrate to ES6, upgrade to TypeScript + AngularJS 1.5+ best practices as OP did, and then follow the official AngularJS -> Angular migration path. Considering they're two entirely different frameworks, Google did a good job creating a usable compatibility layer. This allows a relatively painless "ship of Theseus"-style transition where you have a combination of Angular and AngularJS components interacting with each other, until eventually it's just Angular components and you can drop AngularJS from the build.
atsaloli 6y ago
Max's answer to the interview question "What is the most terrible code that you ever encountered, and what was your approach to refactoring it?" is relevant here. In his book "Code Simplicity", Max has a checklist (summarized in point 4 of https://techbeacon.com/app-dev-testing/rewrites-vs-refactoring-17-essential-reads-developers https://techbeacon.com/app-dev-testing/rewrites-vs-refactori...) -- and that's the checklist referred to in the InfoQ interview.
- atsaloli 6y ago
  Here is the link to the InfoQ interview: https://www.infoq.com/news/2018/01/q-a-max-kanat-alexander/ https://www.infoq.com/news/2018/01/q-a-max-kanat-alexander/
myth2018 6y ago
Agree that you should never rewrite from scratch. However, I believe that almost 100% of rewrites are not actually from scratch: even if not a single line is reused, there will be plenty of experience serving as a foundation. I'm not implying that's always the case. Besides, in some cases, past experience is deliberately not taken into account -- I'm aware of a handful of systems written in procedural languages which performed not that great and were replaced by naive object-oriented implementations. Went really bad.
MattGaiser 6y ago
I suspect that instead of never rewrite from scratch, it is more never rebuild a product from scratch. The problems with all these rewrites went well beyond just changing the codebases.
Tempest1981 6y ago
Before rewriting, create as many tests as possible, so you know what subtle things you broke/changed. Or foist the burden on QA/users to test.
justin_oaks 6y ago
I've heard such thoughts expressed as "Evolution, not Revolution". You evolve (refactor) your old app into the new one, rewriting parts of it at a time. Several comments have already expressed that they've rewritten projects successfully. I've also evolved several projects successfully too. One of the benefits of the evolution approach is that when old bugs resurface, they're less likely to show up all at once since you only changed part of the application. Also it should be easy to compare the code with the bug to the previous code without the bug because it mostly similar. There are times when an application is beyond repair and a rewrite is necessary, but I see those times as the exception rather than the norm.
ChicagoDave 6y ago
There's a Domain-Driven Design pattern that encapsulates this entire problem. First, never even think about rewriting an entire system. You will likely fail. Not because you're not smart and capable, but because the business won't be patient enough to allow you to do it properly. And they'd be right not to be patient. They have things to sell and customers to support...today. That's why Eric Evans came up with the Autonomous Bubble pattern. You rebuild features one at a time and connect them to the old code through anti-corruption layers and translation layers. Over time, the older code will be set aside. In a year or two, the plug will have naturally been pulled on all of the older code. So there's some truth to Spolsky's 2000 blog post. But it's not smart to maintain older code forever either. You have to be careful, thorough, and use the right tools.
- HenryBemis 6y ago
  > They have things to sell and customers to support...today. Deau ex Agile.. knock out one "thing" at a time and let's keep loading the backlog for the next features/etc to be upgraded/rewritten. Tbh in banking I see very few rewrites, most banks (that make their own applications) don't fix it unless it breaks down. They only bother in massive upgrades where modules are rewritten, or an application is replaced one module at a time.
aronpye 6y ago
TLDR Don’t re-write from scratch, refactor instead.
katzgrau 6y ago
Joel classic, and it always reminds me of times I've seen this happen again and again years after it was written. I don't think I've ever seen a full rewrite bring all of its heralded benefits. I'm sure there are some people who have. There always end up being things the old system did better, and sometimes you wind up with the old and new systems running in parallel because end users need to switch back and forth until v2 is finally mature (it seemingly never finally matures). That said, I'm in favor of a rewrite when the use cases for the platform have diverged so significantly that you essentially have to bend it in half to make it do the thing that users want it to today. That is, as some point the core use cases have changed, perhaps via a pivot, and you need to build a product that is essentially new as compared to the old. Regardless, the cases where I've seen a rewrite take place are when the engineers are young, talented, and enthusiastic about new tech and the engineering manager doesn't want to piss them off so they let the devs play (most of them will be off to other jobs in 2-3 years leaving behind a system that is debatable as ugly and busted as the old).
jonnycat 6y ago
Refactoring code is a continuum, from "let's do nothing" (0%) to let's rewrite the whole damn thing" (100%). There's a whole spectrum in between. While I'm a "never say never" kind of guy, I do think many well-intentioned engineers make a leap to the 100% solution too easily. There are lots of other tools in the toolbox that can de-risk the process, like becoming more service oriented, implementing facade patterns, etc., which all in some way or another work towards a "rewrite" usually without ever rewriting everything. Sometimes you get the benefits of the 100% solution with 25% of the work, and without most of the risk. "Yeah, that part of the codebase is old and crufty, but we never have to touch it because it Just Works and there's no point in rewriting it."
- insertnickname 6y ago
  Refactoring is different from rewriting.
  - perl4ever 6y ago
    I think the above implies that it is different, because it is a subset?
fnord77 6y ago
we have a data processing system in production that, for various reasons, will not scale horizontally without major work to the open source framework we're using. Nobody has any appetite to fix the semi-abandoned framework, so if we want to process additional data from bigger workloads, we really have no choice but to rewrite our system. Joel's right - there's a lot of pitfalls. We tried this once and it was a failure. Our 2nd attempt is going much better, though.
pictur 6y ago
I think rewriting a project is an endless curse.
makstaks 6y ago
I'm digging through some legacy code, feeling better about it after reading this.
focus2020 6y ago
Is Joelspolsky overrated ? There is no public code available to verify his competency like JohnCarmack. His writings are more about marketing and general technical knowledge. In my opinion he is overrated.
natmaka 6y ago
Having the developers of an existing code rewrite it using a much newer language & environment they master, with the existing code working rather adequately (but hard to extend and with mediocre performances)... is pleasant and useful. Having a smaller and under pressure team of newcomers w/o any knowledge of the underlying concepts tackling a rewrite while trying to understand and fix a clunky existing code is an ordeal.
citrin_ru 6y ago
It is hard to defend position "never rewrite" (because sometimes rewrite is an optimal strategy), but I see where it comes from: 1. Most programmers when they encounter legacy code have a strong desire to rewrite it from scratch. Especially when it uses language/framework they don't know well. 2. They significantly underestimate the cost of a rewrite and either it takes much more time than estimated or a new system implements a small fraction of old features and/or re-introduces problems fixed in an old system long time ago. It a cognitive bias and we can try to compensate it. Though like with any biases - usually you can see it in others, but cannot correct own behavior.

128 points by HugoDias 6y ago

There are methods for rewriting legacy systems. Articles like this make the job of improving systems more difficult by creating an impassable set of presuppositions among non-technical stakeholders.

dharmab 6y ago

I have successfully rewritten a major codebase. It took about two years to implement. It helped that it involved moving from a mostly proprietary stack to a mostly FOSS stack, which allowed us to leverage the community and spent more time on business features rather than plumbing.

542458 6y ago

I think saying "you should never rewrite code from scratch" is a bit too dogmatic. There's a cost and risk tradeoff. I think people underestimate the cost of a rewrite (Due to ego or NIH or yak shaving), but I don't think it's never the answer. Sometimes the language is so old it's cripplingly expensive to hire programmers in. Sometimes the code is deeply tied to a hardware architecture that is extinct. Sometimes the legacy code actually is that bad. For reference, I've done total rewrites on two different small-ish software projects - in both cases because the original author had made design choices that made the whole thing unsustainable in the long run (no blame implied, it's more about shifting goals). For reference, Twitter has done a total rewrite of their large codebase, and lived to tell the tale.

m12k 6y ago
Yeah, it's probably closer to things like fiddling with assembly, manual thread syncing and rolling your own crypto - it's not that you should never do it, but unless you're very, very sure what you're doing and why, it's probably a bad idea.
wisemanwillhear 6y ago
Indeed. The most successful project I've work in my career was a re-write of a very large internal tool. The choice to "re-write" & re-envision was almost universally regarded as a good choice after the fact. One of the biggest reasons cited was moving to a different tech stack.
shoes_for_thee 6y ago
I hear you. But I think that dogmatically saying "You should never rewrite code from scratch" is just useful enough to catch the vast majority of instances when you should not rewrite code from scratch. I'm willing to be called out for being totally wrong for my dogma in the rare instance that the application should be rewritten from scratch. Every project I have ever joined on, there has been someone who wants to start fresh. There have been a lot of projects. There was one such instance where it was a good idea.

projektfu 6y ago

Always important to mention the alternative, a "Strangler Fig Application", also known as the strangler pattern. https://martinfowler.com/bliki/StranglerFigApplication.html https://martinfowler.com/bliki/StranglerFigApplication.html

mjw1007 6y ago

« It’s important to remember that when you start from scratch there is absolutely no reason to believe that you are going to do a better job than you did the first time » With the benefit of twenty years of hindsight, I think the programmers who performed the rewrite in question did a better job than the original Netscape implementation. Come to think of it, I'm typing this message on the direct descendent of that rewrite, while the competitor to whom they gave « a gift of two or three years » has been forced to abandon their codebase in favour of a third-party one.

tedunangst 6y ago
Firefox has less market share today than Netscape did at the time this was written.
- myth2018 6y ago
  There is a few more competitors today, though.
- larsenwolf 6y ago
  An anecdote I know, but I recently converted from Chrome to Firefox and am actively distancing all of our technology within away from Google.
- sukilot 6y ago
  But the market share was lost to a "rewrite" by a competitor.

S_A_P 6y ago

Never say never, but still a lot of truth to this. I generally think refactoring is the better way to go unless you are backed into an architectural corner. Say, for instance the app was built in power builder and needs to support 64 bit OS. That’s a rewrite in a new language. Say the app was a MacOS 9 and OSX is coming. Rewrite. Otherwise it’s probably better to refactor old code than to chase green fields.

bachmeier 6y ago

Relevant links: https://medium.com/@herbcaudill/lessons-from-6-software-rewrite-stories-635e4c8f7c22 https://medium.com/@herbcaudill/lessons-from-6-software-rewr... And this DHH talk (transcript) https://businessofsoftware.org/2015/10/david-heinemeier-hansson-rewrite-basecamp-business-of-software-conference-video-dhh-bos2015/ https://businessofsoftware.org/2015/10/david-heinemeier-hans...

hn_throwaway_99 6y ago

I'm a big fan of Joel Spolsky's earlier blog posts, but to be honest, I don't think this piece has aged well. If anything, I'm more of the opinion now that you should almost always plan to do a rewrite, eventually. Lots of big companies successfully rewrite stuff all the time. Google is fairly well known for having rewritten large, critical pieces of their codebase over the years. If anything, what should be warned against is big bangs. Netscape's problem isn't that they did a rewrite (which eventually became Firefox, mind you) it's that they essentially abandoned their old code too early, and similarly, they also announced the rewrite too soon. If you're going to do a rewrite, do it quietly, and don't announce it until it's close to ready, and even then you can roll out slowly. For example, the infamous Digg v4 debacle is another example, but the problem isn't that they did a rewrite, it's that they did a rewrite to produce a product nobody wanted, and they burned any possibility of going back after they released it.

MarkSweep 6y ago
Netscape’s big bang rewrite is in great contrast to the current work on Firefox Quantum. Mozilla is slowly rewriting pieces of the browser in Rust to gain better performance and security.
- michaelcampbell 6y ago
  The reason is less important than the methods.
  - the-dude 6y ago
    I can't imagine this to be true.
goto11 6y ago
The more experience I get, the more I think Joel was right. Developers want to believe rewrite-from-scratch can succeed because green-field development is easier and more fun than slowly refactoring inscrutable legacy code. But long before the rewrite project achieve feature parity with the original, it is already marred by the same issues that motivated the rewrite. Because the dysfunction which led to the original code turning into a mess have not been addressed. "But we are smarter than those other guys who wrote this mess" - if that is the case, you should be smart enough to fix the mess.

mojuba 6y ago

I once rewrote a monstrous app that was in development for 5 years (!), in just one month. In terms of LOC it was 20 times smaller than the old codebase. Had the same functionality and then some more. It had zero bugs in the first release, compared to myriad of bugs in the previous one (mostly multithreading related - yes it's hard). All I did was, I dumped Microsoft's COM/DCOM and replaced it with REST; also replaced C++ and VB with C#. Totally made sense to rewrite from scratch and it was a big win with absolutely no downsides. Like, no downsides whatsoever because otheriwse the same month I would have spent fixing maybe 4 or 5 multithreading bugs in the old codebase. Anyway, never say "never do X" because you are most likely wrong.

mamcx 6y ago
This is my experience too. I rewrite often and liberally, and even switch langs (on the side) to check if it can bring huge gains.
gfodor 6y ago
I think this advice is not relevant if you are on a project where it's feasible for a single developer to re-write it in a month. Burning a month on a failed re-write is certainly worth the risk if you take a run at it. For projects where there are several devs going to be working on the re-write for a long time, it almost certainly is a sign that the 'legacy' code has way more knowledge embedded in it than it might seem. Having been on the death march of a re-write before I think the signs are usually obvious when you're in one scenario or the other.
- perl4ever 6y ago
  >I think this advice is not relevant if you are on a project where it's feasible for a single developer to re-write it in a month The implication is that is can be non-obvious if something is potentially that sort of project, as it originally was a large undertaking. I mean, you can assume it's a fake story, but they said it wasn't originally a one person, one month thing. I don't know that it implies the person who rewrites something is a super-genius, it's just that sometimes a new perspective or tools allow a really amazing improvement.

dang 6y ago

From the three dozen or so previous submissions, the actual discussions seem to be: 2013 https://news.ycombinator.com/item?id=6327021 https://news.ycombinator.com/item?id=6327021 2012 https://news.ycombinator.com/item?id=3624830 https://news.ycombinator.com/item?id=3624830 2012 (a bit) https://news.ycombinator.com/item?id=3449953 https://news.ycombinator.com/item?id=3449953 2009 https://news.ycombinator.com/item?id=608431 https://news.ycombinator.com/item?id=608431

winrid 6y ago

A better way to put it IMO is that you should never go dark on your customers during a rewrite.

almostdeadguy 6y ago

Currently on a project where I find myself thinking a lot about this post. I think a lot of the comments here are missing some of the finer points of this argument. "Rewriting" is not per se the problem, "rewriting from scratch" where a project is effectively put on hold until the rewrite gets done, is the real quagmire. There are legitimate ways of doing a rewrite that don't require boiling the ocean and prevent you from shipping. And I'm sure there are exceptions as well, but as a general piece of advice about software engineering I've found this to have a better shelf life than many other nuggets of advice.

dlbucci 6y ago

I completely agree! Throwing away your code and starting over is failing to atone for the sins of the past, and I feel like it prevents you from learning or growing as a programmer. That's why I don't think I'll ever rewrite something from scratch again. To me, this was nowhere more obvious than from my old co-worker who was constantly trying to rewrite the internal site we worked on. First it was angular and coffeescript, but that was apparently unmaintainable after 3 months (!!!). So they rewrote it and then I joined, and it apparently made it to 6 months. Then we tried to rewrite it in TypeScript and React which blew 10 man weeks away before we abandoned it. And then he tried to do TypeScript and Angular again but it never launched. Meanwhile, after the React debacle, I learned my lesson and focused on rewriting and rearchitecting the old code to follow more modern Angular practices (1.5 components and such), and suddenly the code didn't seem so unworkable anymore! Quality improved and features were added that made it a very popular internal site, still in use 3 years after I left that team. So I agree, I think you should always try to improve what you have instead of starting over. (If only our UX designers would go for incremental improvements too...)

rubber_duck 6y ago
Rewriting anything complex and actively used from scratch is not a good idea and the problems have been hashed out may times. Having said that, angularjs and coffescript is a terrible software stack in a dead ecosystem, the best course of action is probably incremental rewrite - React is really good at that because it starts out as a small rendering library and you can incrementally replace stuff like routing etc.
- dlbucci 6y ago
  I completely agree. On my next app, I was forced to use AngularJS (in 2017, somehow), but did get to use TypeScript (which is somewhat hobbled by having to use Angular templates), and this is exactly what we're doing now: rewriting components one-by-one in React. I love refactoring and React is much nicer, so I'm having fun with it :)
- buu700 6y ago
  For that example, I would just use Decaffeinate to migrate to ES6, upgrade to TypeScript + AngularJS 1.5+ best practices as OP did, and then follow the official AngularJS -> Angular migration path. Considering they're two entirely different frameworks, Google did a good job creating a usable compatibility layer. This allows a relatively painless "ship of Theseus"-style transition where you have a combination of Angular and AngularJS components interacting with each other, until eventually it's just Angular components and you can drop AngularJS from the build.

atsaloli 6y ago

Max's answer to the interview question "What is the most terrible code that you ever encountered, and what was your approach to refactoring it?" is relevant here. In his book "Code Simplicity", Max has a checklist (summarized in point 4 of https://techbeacon.com/app-dev-testing/rewrites-vs-refactoring-17-essential-reads-developers https://techbeacon.com/app-dev-testing/rewrites-vs-refactori...) -- and that's the checklist referred to in the InfoQ interview.

atsaloli 6y ago
Here is the link to the InfoQ interview: https://www.infoq.com/news/2018/01/q-a-max-kanat-alexander/ https://www.infoq.com/news/2018/01/q-a-max-kanat-alexander/

myth2018 6y ago

Agree that you should never rewrite from scratch. However, I believe that almost 100% of rewrites are not actually from scratch: even if not a single line is reused, there will be plenty of experience serving as a foundation. I'm not implying that's always the case. Besides, in some cases, past experience is deliberately not taken into account -- I'm aware of a handful of systems written in procedural languages which performed not that great and were replaced by naive object-oriented implementations. Went really bad.

MattGaiser 6y ago

I suspect that instead of never rewrite from scratch, it is more never rebuild a product from scratch. The problems with all these rewrites went well beyond just changing the codebases.

Tempest1981 6y ago

Before rewriting, create as many tests as possible, so you know what subtle things you broke/changed. Or foist the burden on QA/users to test.

justin_oaks 6y ago

I've heard such thoughts expressed as "Evolution, not Revolution". You evolve (refactor) your old app into the new one, rewriting parts of it at a time. Several comments have already expressed that they've rewritten projects successfully. I've also evolved several projects successfully too. One of the benefits of the evolution approach is that when old bugs resurface, they're less likely to show up all at once since you only changed part of the application. Also it should be easy to compare the code with the bug to the previous code without the bug because it mostly similar. There are times when an application is beyond repair and a rewrite is necessary, but I see those times as the exception rather than the norm.

ChicagoDave 6y ago

There's a Domain-Driven Design pattern that encapsulates this entire problem. First, never even think about rewriting an entire system. You will likely fail. Not because you're not smart and capable, but because the business won't be patient enough to allow you to do it properly. And they'd be right not to be patient. They have things to sell and customers to support...today. That's why Eric Evans came up with the Autonomous Bubble pattern. You rebuild features one at a time and connect them to the old code through anti-corruption layers and translation layers. Over time, the older code will be set aside. In a year or two, the plug will have naturally been pulled on all of the older code. So there's some truth to Spolsky's 2000 blog post. But it's not smart to maintain older code forever either. You have to be careful, thorough, and use the right tools.

HenryBemis 6y ago
> They have things to sell and customers to support...today. Deau ex Agile.. knock out one "thing" at a time and let's keep loading the backlog for the next features/etc to be upgraded/rewritten. Tbh in banking I see very few rewrites, most banks (that make their own applications) don't fix it unless it breaks down. They only bother in massive upgrades where modules are rewritten, or an application is replaced one module at a time.

aronpye 6y ago

TLDR Don’t re-write from scratch, refactor instead.

katzgrau 6y ago

Joel classic, and it always reminds me of times I've seen this happen again and again years after it was written. I don't think I've ever seen a full rewrite bring all of its heralded benefits. I'm sure there are some people who have. There always end up being things the old system did better, and sometimes you wind up with the old and new systems running in parallel because end users need to switch back and forth until v2 is finally mature (it seemingly never finally matures). That said, I'm in favor of a rewrite when the use cases for the platform have diverged so significantly that you essentially have to bend it in half to make it do the thing that users want it to today. That is, as some point the core use cases have changed, perhaps via a pivot, and you need to build a product that is essentially new as compared to the old. Regardless, the cases where I've seen a rewrite take place are when the engineers are young, talented, and enthusiastic about new tech and the engineering manager doesn't want to piss them off so they let the devs play (most of them will be off to other jobs in 2-3 years leaving behind a system that is debatable as ugly and busted as the old).

jonnycat 6y ago

Refactoring code is a continuum, from "let's do nothing" (0%) to let's rewrite the whole damn thing" (100%). There's a whole spectrum in between. While I'm a "never say never" kind of guy, I do think many well-intentioned engineers make a leap to the 100% solution too easily. There are lots of other tools in the toolbox that can de-risk the process, like becoming more service oriented, implementing facade patterns, etc., which all in some way or another work towards a "rewrite" usually without ever rewriting everything. Sometimes you get the benefits of the 100% solution with 25% of the work, and without most of the risk. "Yeah, that part of the codebase is old and crufty, but we never have to touch it because it Just Works and there's no point in rewriting it."

insertnickname 6y ago
Refactoring is different from rewriting.
- perl4ever 6y ago
  I think the above implies that it is different, because it is a subset?

fnord77 6y ago

we have a data processing system in production that, for various reasons, will not scale horizontally without major work to the open source framework we're using. Nobody has any appetite to fix the semi-abandoned framework, so if we want to process additional data from bigger workloads, we really have no choice but to rewrite our system. Joel's right - there's a lot of pitfalls. We tried this once and it was a failure. Our 2nd attempt is going much better, though.

pictur 6y ago

I think rewriting a project is an endless curse.

makstaks 6y ago

I'm digging through some legacy code, feeling better about it after reading this.

focus2020 6y ago

Is Joelspolsky overrated ? There is no public code available to verify his competency like JohnCarmack. His writings are more about marketing and general technical knowledge. In my opinion he is overrated.

natmaka 6y ago

Having the developers of an existing code rewrite it using a much newer language & environment they master, with the existing code working rather adequately (but hard to extend and with mediocre performances)... is pleasant and useful. Having a smaller and under pressure team of newcomers w/o any knowledge of the underlying concepts tackling a rewrite while trying to understand and fix a clunky existing code is an ordeal.

citrin_ru 6y ago

It is hard to defend position "never rewrite" (because sometimes rewrite is an optimal strategy), but I see where it comes from: 1. Most programmers when they encounter legacy code have a strong desire to rewrite it from scratch. Especially when it uses language/framework they don't know well. 2. They significantly underestimate the cost of a rewrite and either it takes much more time than estimated or a new system implements a small fraction of old features and/or re-introduces problems fixed in an old system long time ago. It a cognitive bias and we can try to compensate it. Though like with any biases - usually you can see it in others, but cannot correct own behavior.