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| -rw-r--r-- | HACKING | 101 |
1 files changed, 101 insertions, 0 deletions
@@ -233,6 +233,107 @@ Try to make the summary line fit one of the following forms: maint: change-description +Curly braces: use judiciously +============================= +Omit the curly braces around an "if", "while", "for" etc. body only when +that body occupies a single line. In every other case we require the braces. +This ensures that it is trivially easy to identify a single-*statement* loop: +each has only one *line* in its body. + +Omitting braces with a single-line body is fine: + + while (expr) + single_line_stmt (); + +However, the moment your loop/if/else body extends onto a second line, +for whatever reason (even if it's just an added comment), then you should +add braces. Otherwise, it would be too easy to insert a statement just +before that comment (without adding braces), thinking it is already a +multi-statement loop: + + while (true) + /* comment... */ // BAD: multi-line body without braces + single_line_stmt (); + +Do this instead: + + while (true) + { /* Always put braces around a multi-line body. */ + /* explanation... */ + single_line_stmt (); + } + +There is one exception: when the second body line is not +at the same indentation level as the first body line. + + if (expr) + error (0, 0, _("a diagnostic that would make this line" + " extend past the 80-column limit")); + +It is safe not to require curly braces in code like this, +since the further-indented second body line makes it obvious +that this is still a single-statement body. + +To reiterate, don't do this: + + if (expr) + while (expr_2) // BAD: multi-line body without braces + { + ... + } + +Do this, instead: + + if (expr) + { + while (expr_2) + { + ... + } + } + +However, there is one exception in the other direction, when +even a one-line block should have braces. +That occurs when that one-line, brace-less block +is an "else" block, and the corresponding "then" block *does* use braces. +In that case, either put braces around the "else" block, or negate the +"if"-condition and swap the bodies, putting the one-line block first +and making the longer, multi-line block be the "else" block. + + if (expr) + { + ... + ... + } + else + x = y; // BAD: braceless "else" with braced "then" + +This is preferred, especially when the multi-line body is more +than a few lines long, because it is easier to read and grasp +the semantics of an if-then-else block when the simpler block +occurs first, rather than after the more involved block: + + if (!expr) + x = y; /* more readable */ + else + { + ... + ... + } + +If you'd rather not negate the condition, then add braces: + + if (expr) + { + ... + ... + } + else + { + x = y; + } + + Use SPACE-only indentation in all[*] files ========================================== We use space-only indentation in nearly all files. |