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CodingGuidelines: on comparison

There are arguments for writing a conditional as "a < b" rather than
"b > a", or vice versa.  Let's give guidance on which we prefer.

See http://thread.gmane.org/gmane.comp.version-control.git/3903/focus=4126
for the original discussion.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Junio C Hamano 2014-04-30 14:26:23 -07:00
parent 691d0dd0a9
commit 5db9ab82b9

View file

@ -222,6 +222,33 @@ For C programs:
- Double negation is often harder to understand than no negation
at all.
- There are two schools of thought when it comes to comparison,
especially inside a loop. Some people prefer to have the less stable
value on the left hand side and the more stable value on the right hand
side, e.g. if you have a loop that counts variable i down to the
lower bound,
while (i > lower_bound) {
do something;
i--;
}
Other people prefer to have the textual order of values match the
actual order of values in their comparison, so that they can
mentally draw a number line from left to right and place these
values in order, i.e.
while (lower_bound < i) {
do something;
i--;
}
Both are valid, and we use both. However, the more "stable" the
stable side becomes, the more we tend to prefer the former
(comparison with a constant, "i > 0", is an extreme example).
Just do not mix styles in the same part of the code and mimic
existing styles in the neighbourhood.
- Some clever tricks, like using the !! operator with arithmetic
constructs, can be extremely confusing to others. Avoid them,
unless there is a compelling reason to use them.