Re: TRIM_ARRAY

On 2/16/21 7:32 PM, Isaac Morland wrote:
> On Tue, 16 Feb 2021 at 12:54, Vik Fearing <vik@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.

V2 attached.
-- 
Vik Fearing