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It is indeed a sad state of affairs when programmers fail to properly comment as they write code.

Comments should be regarded as an integral part of programming, at least as important as the data and the code. Comments should cover the purpose and meaning of both data and code -- information that doesn't come from reading the code, which can tell you what it is doing, but not why and to what end.

The key to designing good data structures and good code is a clear understanding of their purpose and the objectives. It is good discipline to include comments which describe that much. It is excellent discipline to write those comments, at least in draft form, before defining the data or writing the code -- and then refine data, code and comments together. If it's hard to express the purpose of the data or code, what hope is there of being able to implement it effectively ?

Each subroutine should be commented so that you know what the arguments and return values are and mean, without reading all the code, and looking at everything it calls. You should not have to read all the code to reverse engineer an understanding of what data structures mean and are used for.

Each data structure, each module and each object should contain comments to describe their meaning and purpose. Comments should also cover any key dependencies, assumptions, limitations, caveats, key algorithms, obscure or key background information, etc.

Good commenting can:

  • make you describe what is intended. This helps clarify the problem before coding. It also reminds you, three months from now, what you thought you were doing.

    As you review the code and its associated commentary, it can become obvious that there's a mismatch between what was intended and what's been written. During debugging, the commentary can remind you what was intended... so you don't just assume that what it does is right !

  • make you to consider edge conditions and check that cases that need to be covered are covered. You should do that anyway, of course, but if you write it down it's more concrete.

  • require you to express and examine assumptions.

  • justify and document the choice of algorithm or method.

  • leave notes on things which were not obvious when you worked out what needed to be done or how to do it -- so you don't need to rediscover this in six months time.

  • and so on.

The writing of good comments is not a distraction or an overhead. It should reflect what the programmer must think about in any case -- the discipline of writing it down concentrates the mind, and contributes to the quality of the code. Later on, in maintenance and upgrade, good comments speed up the process of understanding.

I am filled with wonder and admiration for people who can churn out reams of self-documenting code, without having to work out and write down what it is they are doing and why ! Mind you, I prefer to admire them from a (very) great distance.

In reply to Re: Why no comments? by gone2015
in thread Why no comments? by targetsmart

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