On 2/16/21 11:38 PM, Vik Fearing wrote: > On 2/16/21 7:32 PM, Isaac Morland wrote: >> On Tue, 16 Feb 2021 at 12:54, Vik Fearing <v...@postgresfriends.org> wrote: >> >>> The SQL standard defines a function called TRIM_ARRAY that surprisingly >>> has syntax that looks like a function! So I implemented it using a thin >>> wrapper around our array slice syntax. It is literally just ($1)[1:$2]. >>> >>> An interesting case that I decided to handle by explaining it in the >>> docs is that this won't give you the first n elements if your lower >>> bound is not 1. My justification for this is 1) non-standard lower >>> bounds are so rare in the wild that 2) people using them can just not >>> use this function. The alternative is to go through the unnest dance >>> (or write it in C) which defeats inlining. >>> >> >> I don't recall ever seeing non-default lower bounds, so I actually think >> it's OK to just rule out that scenario, but why not something like this: >> >> ($1)[:array_lower ($1, 1) + $2 - 1] > > I'm kind of embarrassed that I didn't think about doing that; it is a > much better solution. You lose the non-standard bounds but I don't > think there is any way besides C to keep the lower bound regardless of > how you trim it.
I've made a bit of a mess out of this, but I partly blame the standard which is very unclear. It actually describes trimming the right n elements instead of the left n like I've done here. I'll be back later with a better patch that does what it's actually supposed to. -- Vik Fearing