On Sun, Apr 4, 2021, at 20:42, Dagfinn Ilmari Mannsåker wrote: > Fabien COELHO <coe...@cri.ensmp.fr <mailto:coelho%40cri.ensmp.fr>> writes: > > >>> The actual source looks pretty straightforward. I'm wondering whether pg > >>> style would suggest to write motd != NULL instead of just motd. > >> > >> That's what I had originally, but when reviewing my code verifying code > >> style, > >> I noticed the other case it more common: > >> > >> if \([a-z]* != NULL && > >> 119 results in 72 files > >> > >> if \([a-z]* && > >> 936 results in 311 files > > > > If other cases are indeed pointers. For pgbench, all direct "if (xxx &&" > > cases are simple booleans or integers, pointers seem to have "!= > > NULL". While looking quickly at the grep output, ISTM that most obvious > > pointers have "!= NULL" and other cases often look like booleans: > > > > catalog/pg_operator.c: if (isDelete && t->oprcom == baseId) > > catalog/toasting.c: if (check && lockmode != AccessExclusiveLock) > > commands/async.c: if (amRegisteredListener && listenChannels == NIL) > > commands/explain.c: if (es->analyze && es->timing) > > … > > > > I'm sure there are exceptions, but ISTM that the local style is "!= NULL". > > Looking specifically at code checking an expression before dereferencing > it, we get: > > $ ag '(?:if|Assert)\s*\(\s*(\S+)\s*&&\s*\1->\w+' | wc -l > 247 > > $ ag '(?:if|Assert)\s*\(\s*(\S+)\s*!=\s*NULL\s*&&\s*\1->\w+' | wc -l > 74 > > So the shorter 'foo && foo->bar' form (which I personally prefer) is > considerably more common than the longer 'foo != NULL && foo->bar' form.
Oh, I see. This gets more and more interesting. More of the most popular variant like a good rule to follow, except when a new improved pattern is invented and new code written in a new way, but all old code written in the old way remains, so less experienced developers following such a rule, will continue to write code in the old way. I sometimes do "git log -p" grepping for recent code changes, to see how new code is written. It would be nice if there would be a grep similar to "ag" that could also dig the git repo and show date/time when such code lines were added. I was looking for some PostgreSQL coding convention document, and found https://www.postgresql.org/docs/current/source-conventions.html Maybe "foo != NULL && foo->bar" XOR "foo && foo->bar" should be added to such document? Is it an ambition to normalize the entire code base, to use just one of the two? If so, maybe we could use some C compiler to get the AST for all the C files and search it for occurrences, and then after normalizing compiling again to verify the AST is unchanged (or changed in the desired way)? /Joel
