From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | pgsql-hackers(at)lists(dot)postgresql(dot)org |
Subject: | Re: POC: converting Lists into arrays |
Date: | 2019-08-08 18:39:18 |
Message-ID: | 9410.1565289558@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2019-07-31 19:40:09 -0400, Tom Lane wrote:
>> That makes the other idea (of a foreach-ish macro declaring the
>> listcell value variable) problematic, too :-(.
> Hm. One way partially around that would be using an anonymous struct
> inside the for(). Something like
> #define foreach_node(membertype, name, lst) \
> for (struct {membertype *node; ListCell *lc; const List *l; int i;} name = {...}; \
> ...)
> which then would allow code like
> foreach_node(OpExpr, cur, list)
> {
> do_something_with_node(cur.node);
> foreach_delete_current(cur);
> }
I'm hesitant to change the look of our loops quite that much, mainly
because it'll be a pain for back-patching. If you write some code
for HEAD like this, and then have to back-patch it, you'll need to
insert/change significantly more code than if it's just a matter
of whether there's a ListCell variable or not.
I experimented with the "aforeach" idea I suggested upthread,
to the extent of writing the macros and then converting
parse_clause.c (a file chosen more or less at random) to use
aforeach instead of foreach. I was somewhat surprised to find
that every single foreach() did convert pleasantly. (There are
several forboth's that I didn't try to do anything with, though.)
If we do go in this direction, I wouldn't suggest trying to
actually do wholesale conversion of existing code like this;
that seems more likely to create back-patching land mines than
do anything helpful. I am slightly tempted to try to convert
everyplace using foreach_delete_current, though, since those
loops are different from v12 already.
Thoughts?
regards, tom lane
Attachment | Content-Type | Size |
---|---|---|
trial-implementation-of-aforeach-1.patch | text/x-diff | 19.7 KB |
From | Date | Subject | |
---|---|---|---|
Next Message | Alvaro Herrera | 2019-08-08 18:40:03 | Re: First draft of back-branch release notes is done |
Previous Message | Bruce Momjian | 2019-08-08 18:35:43 | Re: [Proposal] Table-level Transparent Data Encryption (TDE) and Key Management Service (KMS) |