2014-03-13

On Code Comments

I've been seeing a lot of posts lately on code comments; it's a debate that's raged on for ages and will continue to do so, but for some reason it's been popping up in my feeds more than usual the last few days. What I find odd is that all of the posts generally take on the same basic format: "on the gradient of too many to too few comments, you should aim for this balance, in this way, don't use this type of comments, make your code self-documenting." The reasoning is fairly consistent as well: comments get stale, or don't add value, or may lead developers astray if they don't accurately represent the code.

And therein lies the rub: they shouldn't be representing the code at all. Code - clean, self-documenting code - represents itself. It doesn't need a plain-text representative to speak on its behalf unless it's poorly written in the first place.

It may sound like I'm simply suggesting aiming for the "fewer comments" end of the spectrum, but I'm not; there's still an entity that may occasionally need representation in plain text: the developer. Comments are an excellent way to describe intent, which just so happens to take a lot longer to go stale, and is often the missing piece of the puzzle when trying to grok some obscure or obtuse section of code. The code is the content; the comments are the author's footnotes, the director's commentary.

Well-written code doesn't need comments to say what it's doing - which is just as well since, as so many others have pointed out, those comments are highly likely to wind up out-of-sync with what the code is actually doing. However, sometimes - not always, maybe even not often, but sometimes - code needs comments to explain why it's doing whatever it's doing. Sure, you're incrementing Frobulator.Foo, and everybody is familiar with the Frobulator and everybody knows why Foo is important and anyone looking at the code can plainly see you're trying to increment it. But why are you incrementing it? Why are you incrementing it the way you're doing it in this case? What is the intent, separate from its execution? That's where comments can provide value.

As a side note (no pun intended), I hope we can all agree that doc comments are a separate beast entirely here. Doc comments provide meta data that can be used by source code analyzers, prediction/suggestion/auto-completion engines, API documentation generators, and the like; they provide value through some technical mechanism and are generally intended for reading somewhere else, not for reading them in the source code itself. Because of this I consider doc comments to be a completely separate entity, that just happen to be encoded in comment syntax.

My feelings on doc comments are mixed; generally speaking, I think they're an excellent tool and should be widely used to document any public API. However, there are few things in the world more frustrating that looking up the documentation for a method you don't understand, only to find that the doc comments are there but blank (probably generated or templated), or are there but so out of date that they're missing parameters or the types are wrong. This is the kind of thing that can have developers flipping desks at two in the morning when they're trying to get something done.
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