> Tests are useful, but the big reason that comments are useful is that they are co-located with the relevant code.

That's a not-often-talked-about (that I see anyway?) thing I really like about rust - I don't get to use it much, but when I do I think having 'doc tests' alongside comments heading a function and 'module tests' at the bottom of the same file is great.

Exactly. And then the question remains: why? Why hate comments so much? I never got that

I would conjecture that it has two components:

1. Ancestral memory of programming in languages like assembly or early Fortran where your code was going to be spaghetti because the language was capable of little else, so it had to be drenched in comments that would be unnecessary in a better language.

2. Overreaction to personal memory of overzealous professors who demanded assignments be drenched in excessive comments.

Related to #2, I'm still recovering from high school AP English. We had to meet quotas for a certain number of underlines / notes written in the margin per page. For the better part of a decade I haven't been able to pick up fiction without the feeling that I'm working through a textbook.

Until the code changes, then the comments are usually worse than nothing

No. Comments are like a parity check. If the comments don't match the code, then you know that either:

1) The comments are correct, but the code is wrong. This is a bug. 2) The comments are wrong, but the code is correct. This is equally a bug. Whoever makes the change has an obligation to describe their changes with a comment.

Code with no comments? Could be right, could be wrong, who knows?

Good luck maintaining that.

I wish I could upvote your comment more, but putting it in my bookmarks will have to do for now.

I've seen this counterpoint brought up many times before, but I'm struggling to think of the last time I experienced it. Is it really a common problem for you?

Yes, the issue isn't that most comments are inaccurate, it's that the inaccurate ones are so costly. When the comment doesn't match the code, it makes you question the code and the intent. 90% of the time, comments are accurate or just redundant (the code is descriptive enough), but that 10% of the time when the comments says A and B is happening, I end up chasing down whoever or digging through changelogs and tickets to find the comment wasn't updated.

For the kind of code comment we started this thread talking about (explaining why some simpler/more obvious process is not used), this seems vanishingly unlikely.

Then you fire the coder who changed the code without updating the comments?

Most code doesn't need comments.

That's a waste. Just train them better.