Comments are More Important than Code

CowboyRobot writes "I was going through some code from 2002, frustrated at the lack of comments, cursing the moron who put this spaghetti together, only to realize later that I was the moron who had written it. An essay titled Comments Are More Important Than Code goes through the arguments that seem obvious only in hindsight - that 'self-documenting' code is good but not enough, that we should be able to write code based on good documentation, not the other way around, and that the thing that separates human-written code from computer-generated code is that our stuff is readable to future programmers. But I go through this argument with my colleagues, who say that using short, descriptive variable names 'should' be enough as long as the code is well-organized. Who's right?"

Comments

Gotta document that code...

[TripMaster Monkey]

From the Summary:

...I go through this argument with my colleagues, who say that using short, descriptive variable names 'should' be enough as long as the code is well-organized. Who's right?

You are. No question.

I have a saying I like to use when people (usually managers) try to persuade me to take the quick/cheap way out:


"Any time/money you save by cheaping out now, you'll wind up having to pay back twice over on the back end."

I've yet to see this maxim disproved, and it's just as applicable to coding as it is to anything else. Your colleagues are certainly correct when they state that the code must be well organized, but this simply isn't enough. If you don't put in the necessary time (minimal, really) to properly document your code, you'll wind up spending a lot of time trying to figure out just what you did and why. Also, even if you can remember exactly what your code is all about, the guy that comes after you probably won't...proper documentation is professional courtesy. I suppose they'll learn after they spend a few hours puzzling over a piece of old code (that's how I learned...:P ). Sooner or later, not documenting properly will bite them in the ass.

Re:Gotta document that code...

[jesup]

comments can lie

I worked with a programmer who disliked comments so much he'd remove them before looking at a function. Ok. So I wrote some code and he came to me and said "why do you have an empty else case?" I was puzzled, then realized that I'd written something like this:

else
{
/* we don't have to do anything in the else case because of x y and z */
}

where x y and z would be non-obvious to anyone who wasn't fully immersed in this code. He's run it through a filter that removed all comments. He was a genius programmer - but wrote code that almost no one else could ever maintain. Tons of reliances on edge conditions without comment, reuse of generically-named variables (1 and 2 character names), tricky (but efficient) algorithms. So far as I know, I was the only one there ever to manage to really grok his code, and that required days of immersing myself.

x = x++; // add one to x

is obviously not useful.

// Test FU_E (End bit) after FU_A/FU_B test! If there's a gap, do not consider
// hitting the End bit a marker to stop - continue until we see another
// packet/timestamp (in which case we return TRUE), or until we are
// at the end of the buffer (in which case we return FALSE and keep
// hoping to assemble it).
if (((*curr)->GetPayload()[1] & FU_E_BIT) && !gap)
break; // no error in fragment
// if there's a gap we still won't return true unless
// we find a non-fragment packet (or one from another fragment!)

This is an example of a useful comment - and yes, it has to be maintained if the line of source were to change. I chose that at random; there are better examples - such as explaining what the edge cases are (especially if not handled), and under what circumstances they would become relevant, and how they could be dealt with then.

Please excuse the incorrent indenting above; "<ecode>" doesn't work exactly like 'pre'

Write code like someone else will maintain it

[John Seminal]

that using short, descriptive variable names 'should' be enough as long as the code is well-organized.

This works for code I write that nobody else will ever maintain. Even then I can get tripped up, I'll have to lean back in my chair and try to remember what I was thinking when I wrote the code.

But if you write code you're getting paid for, or code for an organization, anything but personal stuff, write good comments. Variable names might give a good idea about what data the variable holds, but it does not tell us much about how it is used.

When I took my first programming class, the most frustrating part was the documentation. I thought it was retarded and stupid and a waste of time. But now I realize it is very important once you write something more significant than "Hello World".

Joel on Software

[TrueJim]

"There's a subtle reason that programmers always want to throw away the code and start over. The reason is that they think the old code is a mess. And here is the interesting observation: they are probably wrong. The reason that they think the old code is a mess is because of a cardinal, fundamental law of programming:
It's harder to read code than to write it."

From Joel on Software
http://www.joelonsoftware.com/articles/fog00000000 69.html

Always comment.

Comment interfaces, not implementations

[bunratty]

My basic rule of thumb about comments is to comment the interface. In C/C++ this would mean writing the comments at the beginning of all function declarations in .h files instead of .c files, and in Java would mean writing Javadoc comments at the beginning of all methods. The idea is that if you know what a function/method does, you should be able to understand how it does it. The inside of functions/methods should have minimal comments, usually just a one-line comment for each major section explaining what that section does. Sometimes how the function/method works needs to be commented, as in:

void sort(int arr[]); // sort arr, ascending
...
// Uses quicksort
void sort(int arr[]) { ... }

Of course, there are always exceptions. When I was writing low-level code that manipulated hardware registers, I wrote a multi-line comment before each line of bit-fiddling code, complete with what the code did and a cross-reference into the hardware manual. Something like:

// Set the serial port to big-endian mode
// See SlurpSCC manual page 3-5
bitset(slurp->serial, bit(13));

Quality not quantity

[MagikSlinger]

Having RTFA, I can see what he's trying to get at, but as someone who has (unfortunately) found himself spending most of my 10 year career in programming cleaning up other people's poop. At first I thought it was because I must have done something wrong that I kept ending up being assigned this work, but as I came to realise, it was because I make the code better than I found it and I have a knack for fixing stuff other people give up on. I also had silly managers who assign work to the people least qualified to do it.

At any rate, some observations:

1. 20 lines of comments "documenting" your code before you write it (or even after you write it) is far less useful than writing the code COHERENTLY and CORRECTLY in the first place.

Last month, I had a 1200 (yes 1,200) line method with huge blocks of documentation before big pieces of code. I still can't quite tell you what it thought it was doing. The code was a for loop wrapping around code to handle 3 different and mutually exclusive situations. Instead of identifying which of the 3 situations it was and creating a method for each situation, the person just stuffed it all in with lots of comments documenting everything the article's author said. The code was still unmaintainable.

2. Comments are useless unless they are kept up to date

Part of the reason that code was so difficult to figure out was because most of those big verbose documentation comments referred to a completely different implementation. After the programmer had written the first case, she encountered some other bad cases and eventually had to completely change a block of code embedded in this 1200 line for-loop. The code was now correct, but the comments no longer had anything to do with that block of code.

3. Don't be clever when you can be clear

I have made a solemn vow to hunt down and hurt anyone who puts "clever" code in my project. I am so sick of trying to figure out what some obfuscated piece of code in C, C++ or even SmallTalk is doing. And find out it was just a "clever" way of doing something pretty straight forward like iterating over a list. There was no speed gain from the clever trick, and the code wasn't even a bottleneck to begin with. *sigh*

4. If you don't know how to solve the problem, write some experiment code in a separate app to figure it out. Then take the time to do the "right" thing in the production code.

3 days from final for a video game. The CD streaming library for the Sony Playstation was making this strange "hic-up" sound at rare moments. By this time, the original author of this code has long since gone to another company. So I plunge into the code and found that the original programmer didn't know how to write streaming code so he created this hack of a hack of a hack of a test (ad nauseum). The code was programmed by accident, not design. No amount of comment before coding could help this. If the author had dumped the code, wrote documentation describing everything he learned then wrote the code, things would have been a lot better.

5. Unrelated to comments, but use variable names that make sense. Don't name them arbitrarily or to amuse yourself!

That CD sound streamer code I mentioned above used quirky names for variables. Can you tell what "little_ninja" is supposed to be just from the name? When I confronted the coder about this quirk of his (in another library he wrote), he got all huffy and didn't understand why people didn't appreciate his little puzzles or his sense of humor. It galls me he still earns a paycheck in the industry.

There will always be losers

[menace3society]

There will always be loser "programmers" who write code without comments, or write code without useful comments, or modify usefully-commented code without modifying the comments. Everyone I've seen who's ever put up an example of how code is self-documenting and that comments are just extra text saying the same thing have fallen into the second category. Of course things like "prints a message" or "check to see if i==0" are stupid comments. But that's just a straw man if you want to say that all comments are useless (I dare these people to read uncommented assembly of more than about 40 lines, and tell me the code documents itself).

The true useful skill lies in reading sloppy and/or wizardly code. Some people think that they have job security if they write impenetrable code, but then they can just be fired and all their code rewritten. If you can read others' "unmaintainable" code, you enable your employer to save money by not having to rewrite everything the guy they just fired wrote. So they'll want to keep you around as they fire/downsize everyone else. I It doesn't really matter what kind of code you write, since you can read whatever. advise everyone to start reading up on the Obfuscated C Contest, and practice figuring out what evertyhing does. Then you can handle any kind of code thrown at you, and the code you actually write becomes of secondary importance.

I learned the hard way

[amigabill]

My learning experience about commenting code was a difficult one. Like many, while in college I wrote the code and then went back to comment it so the profs were happy.

Then I did a co-op with an automated storage/retreival systems company in their software department. One of the processes involved in a communications system needed some work. The code was licensed from another company in another country. There was no documentation for this communications system. There was very little commenting in the code. Luckily it wasn't in a foreign language. Unluckily it was wrong, apparently the structure of this program was similar to that of another, which was mostly gutted and rewritten, but a few old-program comments survived to be the ONLY comments in the new program.

Sure, the sources could be reverse engineered to provide the documentation required. I did it. It took a few weeks.

After that, I didn't leave comments for last anymore. It's been a good thing. I now work for a semiconductor design company and often write perl scripts or skill-language scripts to automate tedious tasks. I think I'm abou thte only one in the office that comments such scripts in any way. It's nice to read what stuff does when I have to revisit code many months or years later. I hate having to revisit someone else's code because it's nearly guaranteed to be completely barren of anything human-readable.

Listen up kids! Commenting is GOOD! Your professors aren't just being jerks. Learn the easy way and hopefully save yourself a great deal of trouble with your own code. Other people's code will always suck, but your own shouldn't have to.

A database backend would go a long ways...

[mosel-saar-ruwer]

GRANDPARENT: Especially if you change the code and now the comments are wrong

PARENT: You're incompetent if you don't change the comments to match the code. You're equally incompetent if you come across incorrect comments and leave them in. You're supposed to the job, so do it...

PARENT: As Fred Brooks said, "There is no silver bullet."

A database backend would go a long ways towards providing a silver bullet, i.e. if instead of writing your code to an ASCII text file, you were writing to a document management system that kept doubly linked associations between the lines of code and the comments associated with those lines of code, and if code/comment pairs had dirty bits, so that if you changed one [e.g. the code], then the dirty bit wouldn't get changed to clean until you verified that the other [e.g. the comment] was correct, then that would go a long way towards solving the problem.

I think we are still in the infancy of code/documentation/database integration, however.

Re:Even more annoying...

[tomhudson]

What should be done is: Take this 1000 line programme. Add on 5 lines. Add on 20 lines. Add on 100 lines.

Better yet - remove 5 lines. remove 20 lines. remove half the lines ... and it better still work!

Re:Even more annoying...

[rve]

At work, we are not allowed to use comments in the code.

Allowing comments would "encourage coders to use clever tricks" according to the technical director.

Re:Top Ten Code Comment Do's List

[dooglio]

1. Comment each function
- Function name
- what it does
- parameters
parameter name - what is is for and any restrictions on it (i.e., must not be null)
- return value (all possible return values)

****

I really hate having parameters documented in a comment block above the function declaration, because it seldom gets updated when the function signature itself is changed.

I worked with a guy who used to format his functions like this:

void my_func( // My function does foo
int arg1, // arg1 documentation
char * arg2, // arg2 documentation
...
)
{
// Function guts go here
}

The nice thing about this method, although the "look" of a function is broken up, is that when you add or change parameters, the programmer is a lot more likely to change the documentation as well.

When you're under the gun to get the code out, the less the developer has to do to change the docs, the more likely it is they will be changed.

Actually, you illustrate a bigger problem

[Moraelin]

It's not just that the programs to write are small, it's that they're write-only. You write them once, get graded, that's it. We churn generation after generation of students who are taught that code is written once, then never ever maintained.

Sure, you learn lots of things about design, software engineering, etc, in university, but they're pure theory. And seemingly useless theory at the moment. There is _nothing_ to illustrate there why some code organization is good, and why spagetti code is bad. All those lessons about maintenance as wasted when you never have to maintain anything, nor ever write anything big enough.

So while I'll say your idea does have merit, I think it can be done better. Don't just give them 1000 lines of someone else's code. Make them keep building and expanding the same program until the last year.

E.g., ok, in introductory programming they had to write some 100 line trivial program. But don't throw it away. When the next course comes along, give them the assignment to change or expand that original program.

E.g., if at some point you also get a computer graphics course, make them add a graphics module to that program. GUI programming? Sure, add a GUI to it. Database programming? Sure, make it save the data in a database. YACC? Ok, make them add a small scripting language to it. Different language? Make them port it to that language. Etc.

Make it a part of the grade to explain _what_ had to be changed and _why_.

Eventually it _will_ grow to be 1000 lines, and then it will grow even larger. And more importantly it'll be example of why code has to be readable and maintainable.