From 56fe008996bc1a547ce60c8dddd2ca821cac163e Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 28 Sep 2020 20:32:53 -0400 Subject: Add for_each_from, to simplify loops starting from non-first list cells. We have a dozen or so places that need to iterate over all but the first cell of a List. Prior to v13 this was typically written as for_each_cell(lc, lnext(list_head(list))) Commit 1cff1b95a changed these to for_each_cell(lc, list, list_second_cell(list)) This patch introduces a new macro for_each_from() which expresses the start point as a list index, allowing these to be written as for_each_from(lc, list, 1) This is marginally more efficient, since ForEachState.i can be initialized directly instead of backing into it from a ListCell address. It also seems clearer and less typo-prone. Some of the remaining uses of for_each_cell() look like they could profitably be changed to for_each_from(), but here I confined myself to changing uses of list_second_cell(). Also, fix for_each_cell_setup() and for_both_cell_setup() to const-ify their arguments; that's a simple oversight in 1cff1b95a. Back-patch into v13, on the grounds that (1) the const-ification is a minor bug fix, and (2) it's better for back-patching purposes if we only have two ways to write these loops rather than three. In HEAD, also remove list_third_cell() and list_fourth_cell(), which were also introduced in 1cff1b95a, and are unused as of cc99baa43. It seems unlikely that any third-party code would have started to use them already; anyone who has can be directed to list_nth_cell instead. Discussion: https://postgr.es/m/CAApHDvpo1zj9KhEpU2cCRZfSM3Q6XGdhzuAS2v79PH7WJBkYVA@mail.gmail.com --- src/backend/commands/tablecmds.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/backend/commands') diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c index 16285ad09fa..e0ac4e05e5f 100644 --- a/src/backend/commands/tablecmds.c +++ b/src/backend/commands/tablecmds.c @@ -5732,7 +5732,7 @@ ATCheckPartitionsNotInUse(Relation rel, LOCKMODE lockmode) inh = find_all_inheritors(RelationGetRelid(rel), lockmode, NULL); /* first element is the parent rel; must ignore it */ - for_each_cell(cell, inh, list_second_cell(inh)) + for_each_from(cell, inh, 1) { Relation childrel; -- cgit v1.2.3