Re: proposal - plpgsql - all plpgsql auto variables should be constant

pá 24. 4. 2020 v 16:07 odesílatel Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> napsal:

> Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> writes:
> > On Fri, Apr 24, 2020 at 12:24 PM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
> >> plpgsql generate lot of auto variables - FOUND, SQLERRM, cycle's
> control variable, TG_WHEN, TG_OP, ..
> >> Currently these variables are not protected, what can be source of
> problems, mainly for not experienced users. I propose mark these variables
> as constant.
>
> > +1 for general idea.
>
> I'm skeptical. If we'd marked them that way from day one, it would have
> been fine, but to change it now is a whole different discussion. I think
> the odds that anybody will thank us are much smaller than the odds that
> there will be complaints. In particular, I'd be just about certain that
> there are people out there who are changing FOUND and loop control
> variables manually, and they will not appreciate us breaking their code.
>

This is not black/white issue. Maybe can sense to modify the FOUND
variable, but modification of control variable has not any sense. The
updated value is rewriten by runtime any iteration. You cannot to use
modification of control variable to skip some iterations like in C.

> As for the trigger variables specifically, what is the rationale
> for marking TG_OP read-only but not OLD and NEW? But it is dead
> certain that we won't get away with making the latter two read-only.
>

For before triggers the NEW have to be updated. Any other maybe should be
protected, but there is little bit different kind of informations.

> In short, -1. This ship sailed about twenty years ago.
>
> regards, tom lane
>