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>
Junio C Hamano committed
Apr 30, 2014 at 14:26 UTC
5db9ab82b94fab16e69b0228aaf1e972520bd04a
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Documentation/CodingGuidelines
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@@ -222,6 +222,33 @@ For C programs:
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- Double negation is often harder to understand than no negation
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at all.
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+ - There are two schools of thought when it comes to comparison,
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+ especially inside a loop. Some people prefer to have the less stable
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+ value on the left hand side and the more stable value on the right hand
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+ side, e.g. if you have a loop that counts variable i down to the
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+ lower bound,
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+
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+ while (i > lower_bound) {
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+ do something;
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+ i--;
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+ }
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+
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+ Other people prefer to have the textual order of values match the
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+ actual order of values in their comparison, so that they can
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+ mentally draw a number line from left to right and place these
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+ values in order, i.e.
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+
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+ while (lower_bound < i) {
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+ do something;
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+ i--;
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+ }
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+
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+ Both are valid, and we use both. However, the more "stable" the
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+ stable side becomes, the more we tend to prefer the former
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+ (comparison with a constant, "i > 0", is an extreme example).
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+ Just do not mix styles in the same part of the code and mimic
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+ existing styles in the neighbourhood.
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+
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- Some clever tricks, like using the !! operator with arithmetic
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constructs, can be extremely confusing to others. Avoid them,
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unless there is a compelling reason to use them.