Preface
-3
Coding Guidelines
Writing coding guidelines is a very common activity. Whether these guidelines provide any benefit other
than satisfying the itch that caused their author to write them is debatable. My own itch scratchings are based
on having made a living, since 1991, selling tools that provide information to developers about possible
problems in C source code.
The prime motivating factor for these coding guidelines subsections is money (other coding guideline
documents often use technical considerations to label particular coding constructs or practices as good
or bad). The specific monetary aspect of software of interest to me is reducing the cost of source code
ownership. Given that most of this cost is the salary of the people employed to work on it, the performance
characteristics of human information processing is the prime consideration.
Software developer interaction with source code occurs over a variety of timescales. My own interests
and professional experience primarily deals with interactions whose timescale are measured in seconds.
For this reason these coding guidelines discuss issues that are of importance over this timescale. While
interactions that occur over longer timescales (e.g., interpersonal interaction) are important, they are not the
primary focus of these coding guideline subsections. The study of human information processing, within
the timescale of interest, largely falls within the field of cognitive psychology and an attempt has been made
to underpin the discussion with the results of studies performed by researchers in this field.
The study of software engineering has yet to outgrow the mathematical roots from which it originated.
Belief in the mathematical approach has resulted in a research culture where performing experiments is
considered to be unimportant and every attempt is made to remove human characteristics from considera-
tion. Industry’s insatiable demand for software developers has helped maintain the academic status quo by
attracting talented individuals with the appropriate skills away from academia. The end result is that most
of the existing academic software engineering research is of low quality and suffers from the problem of
being carried out by people who don’t have the ability to be mathematicians or the common sense to be
practicing software engineers. For this reason the results of this research have generally been ignored.
Existing models of human cognitive processes provide a general framework against which ideas about the
mental processes involved in source code comprehension can be tested. However, these cognitive models
are not yet sophisticated enough (and the necessary empirical software engineering data is not available) to
enable optimal software strategies to be calculated. The general principles driving the discussion that occurs
in these coding guidelines subsections include:
1. the more practice people have performing some activity the better they become at performing it.
Aristotle Meta-
physics book II
Our attitude towards what we listen to is determined by our habits. We expect things to be said in the ways in
which we are accustomed to talk ourselves: things that are said some other way do not seem the same to all
but seem rather incomprehensible. . . . Thus, one needs already to have been educated in the way to approach
each subject.
Many of the activities performed during source code comprehension (e.g., reasoning about sequences
of events and reading) not only occur in the everyday life of software developers but are likely to have
been performed significantly more often in an everyday context. Using existing practice provides a
benefit purely because it is existing practice. For a change to existing practice to be worthwhile the
total benefit has to be greater than the total cost (which needs to include relearning costs),
2. when performing a task people make implicitly cost/benefit trade-offs. One reason people make
mistakes is because they are not willing to pay a cost to obtain more accurate information than they
already have (e.g., relying on information available in their head rather expending effort searching for
it in the real world). While it might be possible to motivate people to make them more willing pay a
greater cost for less benefit the underlying trade-off behavior remains the same,
3. people’s information processing abilities are relatively limited and cannot physically be increased
(this is not to say that the cognitive strategies used cannot be improved to make the most efficient use
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