Justin Fuller — Software Engineer

Why do we fall into the rewrite trap?

One of my favorite reads is Joel Spolsky's Things You Should Never Do. He wrote this post almost twenty years ago, outlining the downfall of Netscape and others because they spent years rewriting working code. His solution is, unsurprisingly, to refactor. About a year before Joel wrote Things You Should Never Do, Martin Fowler published his popular book, Refactoring: Improving the Design of Existing Code.

So, my question is, if we as a community figured out — twenty years ago — that we should stop rewriting programs, why is it still commonly done today?

Learning To Code

My History

To figure out why we keep falling into the rewrite trap, I want to first step back through a few points in my history.

Cold–what?

My first job was with a fun, scrappy startup called SignUpGenius. Most of SignUpGenius's code had been written before I was even thinking of becoming a web developer, on a platform called Coldfusion (you've probably never heard of it), with a sprinkling of Angular.js. We had no microservices, no Node.js, no React, Go, Docker, or Kubernetes. Our production deployment consisted of arriving early in the morning to manually copy over files and debug issues (I told you we were scrappy).

Yes, this situation is not ideal and, no, I am not advocating for anyone to manually FTP files for their production deploys. However, one thing that cannot be denied is that we were very productive. Granted, the Coldfusion code was old, but we were constantly improving it. There was never talk of a rewrite; instead, the code was improved, little by little, each time we worked on adding a feature or fixing a bug.

The results were clear: in my time at SignUpGenius I was able to see the company gain market share; with increased traffic, revenue, and even a buyout of a competitor.

The code wasn't perfect — far from it, as any codebase would be after ten years — but if we had stopped to rewrite the whole thing we would have been dead in the water and the company would have suffered. Just like in Joel's post, where Netscape took years to rewrite its already working code, rewriting code because Coldfusion was “dead” or “inferior” would have served little business purpose.

I understand there are plenty of counter-arguments to be made here. First and foremost, it gets harder every day to find a Coldfusion developer. Those who know the platform are most likely looking to give a facelift to their skillset, rather than prolonging the inevitable drying-up of the proverbial job pool. More, it may be harder to implement functionality in Coldfusion, particularly the kind we were dealing with, than, say, in .Net, Ruby on Rails, or even Go.

Even so, there are other, better ways to move toward new technology without rewriting an entire codebase.

Taking advantage of new technologies

If I think SignUpGenius was doing the right thing by not rewriting, how, then, how does one take advantage of new technologies?

This brings me to the next chapter of my professional career, when I found myself at FIS Global (the biggest company you've never heard of), working on user experiences with the wealth and retirement division.

Our team found a very specific problem: the websites for 401k plan participants and sponsors were horrendous. Not just in how they looked (but they did look pretty terrible) but also in how participants could interact with them.

The company had built heavily around .NET, which, while it has its merits, did not provide the type of experience that was best for this environment.

To understand why, you must first understand that interactions with your 401k plan are not like your interactions with, say, Amazon. On Amazon, you are probably going to a specific shopping page that you want to load very quickly. You're also probably not very likely to use more than a couple of pages of the website (possibly a search page, a few products, and the checkout). The pages are not necessarily related to each other. There's no reason to load them all up at once, in fact, there's plenty of reasons not to.

However, your retirement website is very different. When you go to it you are not trying to load it as quickly as possible to make an impulsive purchase of some ETFs — you're probably doing your yearly check-in or enrolling for the first time. You'll probably check your balance, your contributions, the performance of your holdings, and maybe even download a few tax documents.

We found that users were coming less often, while spending far more time on the website, using many parts of it — the perfect use-case for a single-page web application. The initial load time was a low priority while seamless transitions between pages were of great value.

So, what did we do? Did we rewrite the whole application? No.

Existing applications’ UI code was refactored, reorganized, and maybe even rewrapped with a framework like Angular. New applications were kept separate and had new code written with the new paradigm.

This allowed for a quick, gradual, and seamless transition from old technology to new, with very little loss of all those years worth of things like tests and bug fixes.

Contempt Culture

Unfortunately, some developers and institutions bank hard on convincing others that a rewrite is the best use of their money. To do this they rely on convincing others of the inferiority of older, battle-tested languages like Java and PHP to newly popular technologies like Node.js or Go.

They don't just stop at “Go is better than Java for this problem” — no, they say Java is always bad, always the wrong choice, and our existing Java projects are terrible messes that need to be rewritten. Maybe, even, the experienced Java developers that we have aren't as good as we once thought.

This is contempt culture and it's prevalent in some software development communities. I know this because I was one of the developers who called old languages terrible, clunky, slow while claiming the superiority of my language of choice.

That is until I started learning about and using some of those older languages.

When I read through Robert Martin's Clean Code Series I was struck by how easy it was to understand the Java and C++ code that he wrote. I realized that the Java and C++ he was writing was far easier to understand than the JavaScript and Go that I had been writing for a few years. The same thing happened when I read through Martin Fowler's Refactoring — he transformed hard to understand, hard to change Java into code that is clear and easy to change to meet new requirements.

After starting a new job at The New York Times — which has amazing code quality, and not just for an organization that is over 150 years old — I found that the company still has some legacy Java and PHP services. I was scared when I heard that I needed to research how to interact with these APIs — until I saw the code. It turns out that these services are so well-factored, with such well-established patterns, that they were incredibly easy to understand. Less than two months into the job and I was able to traverse several of these codebases to find exactly what I needed.

So much for contempt culture, these older languages can be great.

The rewrite

Back to rewrites. I mentioned earlier that some developers rely on convincing their managers that a rewrite is necessary; in some cases, even multiple-year, large team efforts to completely rewrite existing codebases. I've even seen a case where there were multiple rewrites in a row. Did no one stop to think, “if I didn't get it right the first few times, why would I get it right this time?”

No, I don't finally have the right programming language. Maybe I finally have the right team, but probably not.

I think Joel is exactly right with his fundamental, cardinal rule of programming:

It's harder to read code than to write it.

I recently experienced this first-hand. In the codebase I'm currently working with, I encountered an error handling pattern that I didn't like; it seemed cumbersome and convoluted.

My initial thought was to ignore this pattern, rewrite it, maybe even replace it with a better solution. That was until I found that the original author put together an entire talk about this error handling pattern. It turns out that, while it may be a little confusing, it gives incredible transparency when you need to debug with application logs.

The real problem is that I hadn't taken the time to understand how the error pattern worked. I was confused, which led me to dismiss it, rather than to improve it.


👋 Want to learn more about programming? Subscribe to my newsletter to get an update, once-per-month, about what I'm writing about.


When to Refactor

So, if rewrites are so bad, how can you avoid them?

Here's a rule of thumb: If your reason for rewriting the code is that you don't understand it, you should not rewrite it. Instead, you should spend the time trying to understand the code. Once you understand it, refactor the code to make it easier for the next person to understand.

Instead of rewriting the error handling pattern I will probably try to improve a few method names. This brings me back to Martin Fowler's Refactoring. Most of the time, if you feel that a rewrite is needed, you can probably just refactor a few pieces of the program and you'll be in great shape.


If your reason for rewriting the code is that you don't understand it, you should not rewrite it.


Sure, refactoring may have more pieces now than it did when he wrote it — moving an endpoint to another service may be a modern extension to moving a method to another class — but the base concepts are still the same.

More importantly, the benefits are still the same. You will retain all the bug fixes, handled edge-cases, and sparsely-documented features that you don't even know about. They'll still be there when you're done refactoring.

If you rewrite, you'll likely lose much of that. It's an idealistic view of ourselves to think that we understand any large codebase, probably rewritten by several or dozens of developers over months or years, well enough to cover all of these cases in a rewrite. Much of it will be lost.

Hurdles to Refactoring

I used to have a very abstract understanding of refactoring. My manager would ask if I was done with my current task and I would say, yes, but I need to refactor it before it's ready.

What did I mean by that? In the beginning, I had some vague notion of making the code “prettier” or “easier to understand”. They're not bad reasons; if I just wrote code that I can't understand now, I certainly won't be able to when I come back a few months later.

The problem with this approach is that a vague understanding of refactoring comes with a vague understanding of the costs and benefits. Will the next developer agree that the code is easier to understand?

Imagine that you were asked to clean up after a party. If you have never cleaned up before or if it was a big party, it could seem like a daunting task. How do you clean up? Should you remodel the bathroom or should you throw away all the cups and plates? Should you mow the yard, or make the living room usable again by putting all the chairs back at the table?

Books like Refactoring help by giving a clear picture of when and how to refactor. This greatly reduces the cost of refactoring because the possibilities are no longer limitless.

For example, here are a few concrete refactoring reasons and solutions:

Reason 1: The code is hard to understand. I don't know where to make my change.

Solution 1: Read through the code; add tests where there are none; then, once you understand their true purpose and have added tests, improve variable or function names.

Reason 2: Making this change will touch many parts of the codebase, otherwise known as shotgun surgery, I'm worried something will break.

Solution 2: Rearrange the codebase so that your change will only have to modify one or a few pieces of the code.

You can use code smells and their specific solutions to greatly reduce the abstract-ness of refactoring. Refactoring can become a quick, concrete tool that you use to accomplish specific purposes.

Backward Refactoring

I used to think refactoring was done after I finished coding. I finished my work, I made some concessions in the name of “Make it work, make it right, make it fast", now I need to clean up.

However, refactoring can be a better tool before you begin making any changes as a way to make your change easier. As Kent Beck said “Make the change easy (warning: this may be hard), then make the easy change.”

Think about when you refactor after making your changes. What are you doing? You're guessing what will be needed by the next person or the next change to the code. You're guessing what will be misunderstood or unclear to the next developer. You might be right, but you also might be wasting everyone's time.

When you refactor before making a change you have a clearer picture of what is misunderstood, what change needs to be done, and why it's difficult to accomplish.

For this reason, I suggest another rule of thumb: Prefer refactoring before you make a change, rather than after.

When to rewrite

As always, things aren't perfectly black-and-white. There are a few times when a rewrite might be necessary.

The golden opportunity to rewrite less-than-stellar code is when the business wants to re-think how the product works. If the business is unhappy with the product and the developers are unhappy with the code, this may be the perfect opportunity to rewrite. Rewrite for better functionality, rather than better code. However, unless you're in a fast-moving startup, this opportunity may not come very often as most companies that I've worked with prefer incremental change.

This is one reason that, as Sam Newnan writes in Building Microservices, some people suggest to keep microservices small enough to rewrite in 2 weeks or less. There's no huge loss if a total overhaul is needed. You could rewrite it during a slow season.

There's another opportunity, which (I hope) is even rarer than the last case. Sometimes a development team has written code that is so bad, so convoluted, that even they can't understand it enough to make a single change without creating a slew of bugs. If this is the case, a rewrite may be unavoidable.


Rewrite for better functionality, rather than better code.


However, let me caution you even in this case. If the composition of the team has not drastically changed; if there is not a clear definition of the cause and solution to the last iteration's problems; or there is not new leadership that provides clearer vision, principles, and guidance — you will likely repeat the same mistakes all over again. If the people haven't changed, the circumstances haven't changed, and the practices haven't changed, what will be different this time?

Key Takeaways

Yes, all of this was just to say that you should prefer refactoring over rewriting. If you couldn't tell by all the times I linked to it, I highly recommend Martin Fowler's Refactoring to learn more about the subject.

Here are the key takeaways:

  1. Prefer refactoring over rewriting.
  2. If your reason for rewriting the code is that you don't understand it, you should not rewrite it.
  3. Prefer refactoring before you make a change, rather than after.
  4. Rewrite for better functionality, rather than better code.

Hi, I’m Justin Fuller. I’m so glad you read my post! I need to let you know that everything I’ve written here is my own opinion and is not intended to represent my employer. All code samples are my own.

I’d also love to hear from you, please feel free to follow me on Github or Twitter, or subscribe to my newsletter to get an update, once-per-month, about what I'm writing about. Thanks again for reading!