Re: Using Expanded Objects other than Arrays from plpgsql

Hi, Michel and Tom!

On Sun, 26 Jan 2025 at 23:04, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Andrey Borodin <x4mmm@yandex-team.ru> writes:
> > On 26 Jan 2025, at 20:37, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> Maybe we should recast it as an action.  What do you think of
> >> "mark_expr_as_assignment_source"?
>
> > Sounds better to me. I found no examples of similar functions nether in pl_gram.y, nor in gram.y, so IMO
mark_expr_as_assignment_source()is the best candidate.
 
>
> WFM, I'll make it so in next version.
>
> > Got it, many thanks for the explanation.
>
> I'll see about incorporating more of that in the comments, too.
>
> > I wonder if you plan similar optimizations for array_cat(), array_remove() etc?
> > +   a := a || a; -- not optimizable
> > Why is it not optimizable? Because there is no support function, because array_cat() has no support function, or
somethingelse?
 
>
> plpgsql won't attempt to optimize it because "a" is referenced twice
> and there is no support function that might say it's safe anyway.
>
> array_cat doesn't currently have any special smarts about expanded
> arrays, so it's all moot because the arrays would get flattened
> on the way into it.  If we did improve it to be able to cope with
> expanded arrays, I'm not real sure that it could safely manage an
> in-place update where the two inputs are the same array --- at
> the least, some extreme care would be needed to get the right
> answers.
>
> I'm not real excited about optimizing additional array operations
> anyway.  Maybe some more will get done at some point, but I don't
> see that as part of this work.
>
>                         regards, tom lane

I started looking at the patchset.
Recently it got conflicts with changes to yyparse (473a575e05979b4db).
Could you rebase it and also do naming changes proposed by Andrew
Borodin, which I definitely agree with?

Regards,
Pavel Borisov