The code etymologistPart 7: Technical decisions

I'm personally a big supporter of self-explanatory code. I spend a lot of time thinking about suggestive and intuitive names, designing and structuring the code so my team mates have an easy time understanding what it does.

However, there are various categories of information that cannot be incorporated into code. Therefore, we often need to fallback to written text, usually as code comments or external documents.

Let's see some examples.

Code comments

Sometimes we spend a lot of time debugging and fixing a problem. We often end up learning and discovering new information during these adventures.

At times, the fix itself could be very simple or short. The code itself could be intuitive regarding what it does, but it's not obvious why is it needed.

Therefore, it helps a great deal to write down the decision to add that fix, to record the knowledge that came along with finding the solution for the problem.

{
  // ...
  /**
   * !IMPORTANT: Jest apparently needs a lot of memory.
   * Node 16.11 introduced a memory leak, effectively depleting the entire heap.
   * The tests fail with "JavaScript heap out of memory" on 4GB machines, and sometimes even on 8GB.
   * https://github.com/jestjs/jest/issues/11956#issuecomment-994914988
   *
   * The problem has been fixed in Node 20.10: https://github.com/nodejs/node/releases/tag/v20.10.0
   * We're currently using Node 20.15, but the issue is still present.
   * The heap reaches 2.7GB (instead 3.5GB with Node 16.18).
   *
   * Jest 29 exposes a workaround which seems to work, since it keeps the heap at a constant value:
   * https://jestjs.io/docs/configuration/#workeridlememorylimit-numberstring
   */
  "workerIdleMemoryLimit": "1GB"
}

In the example above, the fix itself is a single line of code, which is pretty intuitive. However, the comment above explains and communicates so much more:

• what was the initial problem, linked to the official issue report;
• fix attempts that didn't work;
• links to detailed documentation for the final solution.

Deprecations

Existing requirements are often changed by product teams. At the technical level, this might require data migrations. To better exemplify, let's take a concrete scenario.

Let's consider that we have a UserSettings model that contains the isDarkTheme field, among others. This works as expected for "light" and "dark" values, since it is a boolean. But once we introduce a third option, like "system", we need to make some changes:

• change its type to allow specific values;
• change its name to theme to better reflect its meaning;

type UserSettings = {
  theme: "light" | "dark" | "system"; // new field
  isDarkTheme: boolean; // old field
};

Ideally, we would completely remove the old isDarkTheme field. However, we might have to keep it longer for backwards compatibility. So, now we have two different fields that contain pretty much the same information.

But how do we communicate to all developers and consumers of the code which field should they use? Verbal communication and cognitive load work at small scale, but they have their limitations.

Fortunately, TypeScript provides a simple way to mark code as deprecated using JSDoc syntax:

type UserSettings = {
  theme: "light" | "dark" | "system";

  /** @deprecated use `theme` field instead */
  isDarkTheme: boolean;
}

This is a standard way to signal that a certain code should not be used anymore. Additionally, we can also provide guidance to alternative solutions. We're not only documenting that this field should not be used, we're also telling others what to do instead.

Furthermore, we can experience the effects of this approach on the consumer side as well. When accessing a deprecated property, the code editor will:

• add a strikethrough style on the deprecated field signaling that it shouldn't be used;
• display the code comment when hovering the property, so consumers know how to fix the deprecation;

It's worth mentioning that using deprecated code is not a type error in TypeScript. If we want to prevent consumers from using deprecated APIs, we can enable the no-deprecated TypeScript ESLint plugin.

Architectural Decisions

Some technical decisions might not be that isolated. They might have system-wide effects at the architectural level. A better place to document such decisions is next to other product-related documents.

Such documents are ofted called Architectural Decision Records (ADR). There are various standard formats that can be used, however the most important thing to remember is the practice of documenting the important decisions, the reasons behind the chosen solution, and the alternatives taken into consideration that were eventually discarded.

Requests For Comments

Some technical decisions are not clear from the beginning and might need some iterations before a final decision is made. We start from an initial proposal, collect feedback, and iterate until a consensus is reached. This process is often refered to as a Request For Comments (RFC), a term introduced by The Internet Engineering Task Force (IETF) in 1969.

Depending on the type of software, RFCs can be large documents, where only the table of contents spreads over multiple pages, like the RFC 2616 for the HTTP/1.1 protocol.

In contrast, React also adopted RFCs as a standard practice to introduce new features. They follow a much simpler format, inspired by Rust RFC Process.

At the application level, some proposals suitable for an RFC, include:

• Changing the branching strategy;
• Changing the project's file structure from packaging by type to package by feature;
• Setting strict type-checking for the TypeScript compiler;
• Migrating to a monorepo solution, etc.

If you have a difficult time understanding when to choose between Architectural Decision Records and Requests For Comments, here's a great comparison between ADRs and RFCs. The article also includes an easy-to-follow diagram at the end.

The bottom line is that not all code can be self-explanatory. Writen documentation in the source code or in a separate document is often needed to record important technical decisions.

Continue reading Closing thoughts