Yanglin Zhao

hi (at) yanglinzhao.com

Messy toolbox

The Problem

Today, I want to talk about a problem that I think pervades a lot of codebases that's relatively easy to fix. Chances are you've come across it in one form or another. I'm talking about the catch-all, kitchen sink module that contains all the reusable functions for a project. They are usually named utils.py, helpers.js, or common.rb depending on the language.

While the intention of pulling commonly used logic into a helper/utility module makes sense on paper, I will contend that having a utils module is generally a bad idea.

Growing without bounds

What I've personally observed is that the module starts off on the right track with just a couple of functions. But given moderate amount of time and number of engineers working on the codebase, you'll find that the utils module will grows seemingly without bounds. It becomes a mish-mash of all sorts of one-off functions. You start to get an uneasy feeling about adding any new functions to the pile because you begin to lose sense and judgement of whether your new function should even belong there. In its worst form, it may start to resemble an software equivalent of an episode of hoarders.

I think the reason why the contents of these utils module grows out of bounds is because of the name itself. util is just too loose of a name; it gives no guidance about what should or should not belong in it.

We all know that naming is a difficult but vitally important aspect of programming. It conveys our intentions to other programmers or our future selves. If we look at utility modules from that lens, we can see that the naming of utils does not really communicate anything useful about what it should contain.

Names should be narrow. It needs to give us programmers a sense of its domain and communicate about things that it can and can't represent.


Fortunately, if you do happen to have this growing pile of utils module in your project, we can apply some relatively easy and incrementally adoptable fixes.

Solution 1: Split the utils module up and give each submodule a good name.

If the problem is one of naming being too loose, the obvious solution is to come up with a better names.

Chances are, if you have a large utils module, they can be separated into logical groupings. For example, in a hypothetical web application codebase, There may be a set of functions that deals with array manipulations, some that handles structuring logging data, and some functions that handle input validation. In this cases, the easy way out would be to just create sub-modules within util with a name about its logical domain.

// Before
import { flatten, getLogger, validateAddress } from "./utils.js";

// After
import { flatten } from "./utils/array.js";
import { getLogger } from "./utils/logging.js";
import { validateAddress } from "./utils/validation.js";

Seems simple and obvious enough, but I think just giving it a good name does help everyone who works on the project implicitly understand what should or shouldn't be in these sub-modules.

Solution 2: Create a unstable_temporary_utils module.

As a supplement to solution 1, something that I've found helpful is to create a utils-like module but a bit more verbosely named unstable_temporary_utils, with the expectation that it is only a transient home for functions until we can find a better module to place it in.

If I reflect on some of my own temptations to add a utils like catch-all module, it happens when I'm exploring a new feature or domain and I just don't know where something belongs yet. Being able to come up with a good, narrow name can very much be a chicken and egg problem of having to spend enough time fleshing out code and fixed some corner case bugs for a new domain/feature.

Placing a strict policy of never have a kitchen sink modules and always needing to properly name things may be setting ourselves up for failure. It may lead to premature/wrong abstraction early on in the process. I've found that having a given module designated as a "lost and found" of sorts can be a good mechanism for the team to temporarily put logic and defer actually coming up with a good name, as long as it's understood that we'll have to revisit and find a proper home for it.

// unstableTemporaryUtils.js

function parseAuthToken(request) {
  // ...

Given a contrived example above of a parseAuthToken function, we can give it some time to settle into the codebase and realize that utils/auth.js maybe a more suitable module for it.

// utils/auth.js

function parseAuthToken(request) {
  // ...

The unwieldy name is on purpose

I want to note that that long and awkward naming of unstable_temporary_utils is very much intentional here. It lets us easily track its usage via git grep. More importantly, it also subtly applies a certain sense of pressure and shame whenever you import from unstable_temporary_utils. We want it to be a module of a last resort, and give you a little bit of pause and thought on whether you really want to put a new function in there.

Sometimes that pause may give you the opportunity to actually come up with a good name. Or perhaps you realize that not creating an abstraction and living with the duplication is perfectly ok.

Prevent unchecked growth

If you do happen to adopt this approach, I also recommend adding a linting step in CI that will fail the build if the unstable_temporary_utils module exceeds a certain size. This will help us draws a line in the sand and prevent the module from exceeding a certain size and avoid the same fate as an ever expanding utils module.

It's all about alignment

At the end of the day, programming is really just about communication to other fellow humans. I really encourage you to look at how you name function/modules/services and approach it from the lens of if your teammates or future self can reasonably articulate if something should or shouldn't belong in it.

And if you find that you've fallen into the utils module trap, you can fix it but giving it better names/boundaries, which has the invaluable side-effect of realigning your teammates on the purposes of certain module, which I've found to be invaluable for the longevity of a project.