[bhauer]

Agreed. Explicitness and comments are very useful in understanding the intended functionality and logic, whether or not the code actually implements that intent correctly (an in providing that intent, they can help identify bugs earlier than they would be identified otherwise).

[dskrvk]

But comments go out of date, and the compiler doesn’t check them against the implementation. To document + enforce the intended functionality, use tests.

[Ferret7446]

Outdated context is miles better than no context in my experience. As long as the comment isn't intentionally misleading, it always helps a ton in piecing together what happened, even if the comment is factually wrong when it was written, because I can tell how the original author was mistaken and why it led to the current code.

[mook]

Outdated comments are great, because it means you probably have a bug right there. If the comment didn't get updated, the code change probably didn't look at all the context and missed things.

Pretty sure I'm guilty of that pretty often.

[irthomasthomas]

Looking at someone else's code, how would you know which was out of date, the code or the comment?

[mook]

Does it matter? If the comment doesn't match the code, there's a bug (in the comment or the code). Either way you need to spend time to understand the context and figure out the correct thing, not trusting either.

[mumblemumble]

Looking at the commit history is a great start. Especially if your team actually empowers people to reject code reviews when the commit messages are unclear or insufficiently detailed.

[Vegenoid]

git blame will show when lines in a file were last changed, and the commit that changed them

[marcus_holmes]

Comments (should) explain the "why" not the "what". The "why" doesn't go out of date, even if the "what" does.

[kmoser]

Generalizations like that are theoretical, and don't always align with reality. There's nothing wrong with comments summarizing the "what", and in fact doing so is a good thing because it can describe anything from the intention of the code to the business logic. "This function merges array X with array Y, converting all the keys to lowercase because they will be used later by foo()."

The "why" can go out of date, e.g. "do X before Y because [specific thing in Y] is dependent on [specific thing in X]". If you rewrite Y to no longer be dependent on X, the comment is now out of date.

The reality is that any comment can go out of date at any time if the code it describes changes enough. But that's really no excuse for failure to maintain comments. Sure, in reality code is messy and inconsistently written, not even counting comments. Comments are an essential parts of your codebase, and while they are used exclusively by humans, that doesn't mean they are any less worthy of being updated and cultivated.

[jjnoakes]

The why can also go out of date. Maybe not as frequently? I don't have a great intuition for the ratio, but it is certainly more often than never.

[marcus_holmes]

I dunno, the "why" for me is "why are we doing this, and doing it this way?". If that changes, but somehow the comment isn't changed, that would feel really strange. It's not just tweaking a few lines, it's rewriting the whole routine. If all the code changed but not the comment, that would have to be deliberate, and definitely picked up in code review.

Though, obviously, accidents happen, etc. But then that also happens with tests and everything else. I have definitely seen out-of-date tests in code bases, where the test is no longer relevant but still maintained.

[knappe]

So I actually find this helpful because if the why doesn't match the what (code), I know to look back at the history of changes and see why there is a mismatch. This is honestly a great signal that something might have gone sideways in the past while I'm trying to triage a bug or whatever. So even if the comments are out of date, they're still helpful, because I know to go look at why they're out of sync.

[marcus_holmes]

really good point, and well worth mentioning in the "code should be self-documenting and comments are unnecessary" debate.

[dijksterhuis]

tests -> verify intended functionality implementation (the how is right).

comments -> why intended functionality was implemented that specific way (marketing wanted X because of Y, so we had to do it like Z with a bit of A).

> But comments go out of date

Just like updating the tests when code is changed, update the comment when the code is changed.

[jackjeff]

Comments go out of date because of bad developers.

The same people who do the bare minimum for tests not to explode. But won’t add a new test case for the new branches they just introduced.

The same people who will mangle the code base introducing bizarre dependencies or copy paste the same piece of code rather than refactor.

People who fail to handle errors correctly. My favorite: by wrapping code in a if statement without an else. (else? Get a weird error without logs! Miles away from the call site!)

People who don’t validate inputs.

People who don’t give a monkey about adding context to errors making the thing impossible to debug in prod when they explode.

People who are too lazy or in incompetent to do their job properly and will always jump at the opportunity to save 5 minutes now but waste 5 hours of everybody else’s time later. Because of course these people can’t fix their own bugs!

And of course these are the people who make comments go out of date. I’ve seen them implement a thing literally the line below a TODO or FIXME comment and not delete the line.

Comments going out of date is a shit excuse for not writing comments as far as I’m concerned.

The fact that some people are incompetent should not drive engineering decisions. You should always assume a minimal level of competency.

[dijksterhuis]

> Comments going out of date is a shit excuse for not writing comments as far as I’m concerned.

I agree.

> Comments go out of date because of bad developers

I disagree.

Comments can also go out of date because

- developer is having a really shit time atm and their head is not in the game (bad looking after people management)

- developer is on a one day a week contract and doesn’t have the time in their contract to write big header comments explaining nuances (bad strategy)

- developer thought it looked obvious to them but it’s not obvious at review time (developer is being classic human)

- developer is getting pushed to deliver the thing now now now (bad workload management)

Most of those are the result of some decision made by someone who was not the developer (they’re all real cases). And they are the “non-code blockers” that good managers solve for us, so we can focus on getting good stuff done.

I’ve been where it seems like you are at. Blaming others for being bad didn’t help me. I had to lower my expectations of others, keeping my expectations for myself. Then get on about teaching willing people how they could be better. Might be making a few assumptions/projecting a bit there, but that’s my experience with “bad developers”.

Being any type of “leader” is lonely. Whether that’s an official role assigned to you or not. Or if it’s just a skill level thing. No one can quite match up to the expectations or understand what we see and why. But explaining it goes a long way with the right ones.

[jgwil2]

> Just like updating the tests when code is changed, update the comment when the code is changed.

Well, yeah. But the point is that tests can be run in a pipeline that can fail if the tests fail. Comments going out of date has to get caught by a human, and humans make mistakes.

[dijksterhuis]

> humans make mistakes

All software is built by humans in some way. All software has mistakes.

Perfection is an impossible goal.

[jgwil2]

Yeah but there's a fundamental difference between something like tests that can be checked automatically and comments, that have to be checked manually. Because of this, it can be assumed that comments will eventually go out of date.

[dijksterhuis]

Good PR review from a skilled and more senior developer catches these things, most of the time.

Just like how tests catch functionality issues , most of the time — bugs still exist in tested software, because people make incorrect assumptions about how/what to test, or implement the test wrong.

> it can be assumed that comments will eventually go out of date.

Don’t make assumptions. That’s just a lazy excuse for not trying.

The same thing could be said for tests

> it can be assumed that tests will eventually go out of date

So why should we bother updating tests? They’re just going to go out of date?!!

Because it makes the codebase easier to work with for someone brand new.

Same as comments.

Pay down the debt for the next person. The next person could even be you in a year’s time after working in a completely different project for 9 months.

[consteval]

Tests only test functionality, they don't test business context. Comments explain business context.

For example, "we have this conditional here because Business needs this requirement (...) satisfied for this customer"

Your comment can test the logic works correctly. But someone coming in, without the comment, will say "why are we doing this? Is this a bug or intentional? Is the test bugged, too?"

Now, they'll see it's intentional and understand what constraints the code was written under. Your test can't send a slack message to a business analyst and ask them if your understanding is correct. The original dev does that, and then leaves a comment explaining the "why".

[worik]

> To document + enforce the intended functionality, use tests.

Tests go out of date

Tests increase the maintainince burden

The compiler does not ensure code is tested

Tests get duplicated

Mēh! Tests matter, and testing is very important. Good judgment is required

Just like comments.

Writing code requires professional care at every step. The compiler helps of course see, but being professional is more than writing code that compiles

It involves documents too. And tests. Not too many (tests or documents) but not too few

Undocumented code is an enormous burden to maintain (I am eyebrows deep in such a project now). It is not enough to just write code and tests, documents including inline comments, are crucial

[runevault]

Note in Rust if you include comments with code that will run as tests but be inline in your main code instead of having to find the relevant test function to confirm functionality.

https://doc.rust-lang.org/rustdoc/write-documentation/docume...

[rob74]

Go has something similar: functions marked as examples that are both run as tests and shown and run as examples in the documentation (https://go.dev/blog/examples)

[runevault]

Interesting. I don't know when that was implemented in Rust but clearly Go has had it for a long time, since that post is dated 2015.

While things like syntax are important, languages adding tooling like this (along with stuff like package managers) is so important to the continued evolution of the craft of software development.