[anigbrowl]

I look to comments to tell me what a block of code is doing rather than why, eg 'Performs a Discrete Cosine Transform on the contents of the buffer' or 'Bubble sort algorithm rearranges the records in at least as much time as required to enjoy a nice cup of tea.'

The 'why' of a very low-level tools like this is the sort of thing that needs to be explored at length in a paper or (in this case) a book, otherwise they'll swamp the actual code. Sometimes as a learning exercise I'll take something like this and comment the hell out of everything, but the value there is more in writing the comments than trying to read them again later. Of course this is very much a matter of personal taste.

[aeonsky]

I am a junior dev without a ton of experience so correct me if I'm wrong, but I strongly disagree. Comments should explain "why" something was written. Wouldn't the function name indicate what you are doing (and comments in the function)? This is especially true in business logic.

reverseNaturalSortOrder(listOfItems); // case sensitive sort of items by reverse alphabetical order

or

reverseNaturalSortOrder(listOfItems); // sort this way because the upper layer expects items in reverse order since user requested it

I think it is usually significantly easier to understand what something is doing rather than why it is doing that. To answer the former it usually requires a narrow scope of focus, but the latter requires a very broad scope.

[DSMan195276]

I agree with you completely - The code explains what you're doing, comments explain why you did it that way. Ideally, any comments that explain what you're doing would end-up being redundant when looking at the code.

I think this code details a special case of the above though, in that it comments what the enums are instead of just naming the enums. I give that a pass strictly because this code needs to be able to compile itself, and I don't think it supports named enums, so the comment was necessary to make up for that.

[MrTortoise]

Its not that simple though, error fixes and edge cases often obfuscate something that was understandable. A why comment is never bad, but a what comment is often as valuable as a test

[DSMan195276]

Like I noted with my special case, it's not always that simple, but I routinely find the best commented code to be code which was written with the comments explaining why and the code explaining what. There are definitely time where a what comment is warranted, but it's just not the general case.

[moron4hire]

That should almost never be the case. If you find this to be a frequent occurrence, then the code base in which you are working is not designed for the problem domain to which it is being applied.

[anigbrowl]

Sure, I'm not arguing against ever saying why you'd do something :) I just like descriptive comments because it speeds up the business of figuring the high level structure of the code - you're right that understanding exactly what's going on can be the most difficult part, but for me that answer usually falls out as I build a mental model of what it's doing. On the other hand some algorithms need in-depth explanation that's beyond the scope of comment (hence my example of the transform).

Mind, I mostly do hobby/experimental programming, I've just been doing it for a long time. So I'm not commending this as a work practice or anything - your point about business logic made good sense.

[tdsamardzhiev]

Agreed - code should explain what code does. Duh.

[chipsy]

There are three levels to consider:

1. Readability for modification

2. Readability for the "what"

3. Readability for the "why"

All human-readable description in code is there to make the difference between having a piece of documentation pointing you in the right direction, and having to reverse engineer your understanding. It's an optimization problem with definite tradeoffs. Although CS professors and many tutorials will tend to encourage you towards heavy description, over-description creates space for inconsistent, misleading documentation, which is worse than "not knowing what it does."

When you see code that is dense and full of short variables, it's written favorably towards modification. It is relying on a summary comment for "what" it does, and perhaps on namespaces, scope blocks, or equivalent guards to keep names from colliding. Such code lets you reach flow state quickly once you've grokked it and are ready to begin work, because more of it fits onscreen, and you're assured the smallest amount of typing and thus can quickly try and revise ideas. The summary often gets to stay the same even if your implementation is completely different. And if lines of code are small, you enjoy a high comments-to-code ratio, at least visually.

Code that builds in the "what" through more descriptive variable names pays a price through being a little harder to actually work in, with big payoffs coming mostly where the idea cannot be captured and summarized so easily through a comment.

In your example, one might instead rework the whole layout of the code so:

    var urq; /* user request type */

    ... (we build list "l") 
    
    /* adjustments for user request */
    {
      if (urq=="rns") { /* case sensitive sort by reverse alphabetical order */ ... }
    }

If you aren't reusing the algorithm, inline and summarize. And if you're writing comments about "what the upper layer expects", then you(or your team) spread and sliced up the meaning of the code and created that problem; that kind of comment isn't answering a "why," it's excusing something obtuse and unintuitive in the design, and is a code smell - the premise for that comment is hiding something far worse. If the sequence of events is intentionally meaningful and there's no danger of cut-and-paste modifications getting out of sync, it doesn't need to be split into tiny pieces. Big functions can be well-organized and easy to navigate just with scope blocks, comments, and a code-folding editor.

"Why" is a complicated thing. It's not really explainable through any one comment, unless the comment is an excuse like the example you gave. The whole program has to be written towards the purpose of explaining itself(e.g. "literate programming"), yet most code is grown organically in a way that even the original programmers can only partially explain, starting with a simple problem and simple data and then gradually expanding in complexity. Experience(and unfamiliar new problem spaces) eventually turns most programmers towards the organic model, even if they're aware of top-down architecture strategies. Ultimately, a "why" has to ask Big Questions about the overall purpose of the software; software is a form of automation, and the rationale for automating things has to be continuously interrogated.