Re: [HACKERS] [PATCH] Generic type subscripting

On Mon, Nov 30, 2020 at 2:33 PM Dmitry Dolgov <9erthalion6(at)gmail(dot)com> wrote:
> > On Fri, Nov 27, 2020 at 12:13:48PM +0300, Alexander Korotkov wrote:
> > I've started to review this patch.
>
> Thanks!
>
> > My first question is whether we're
> > able to handle different subscript types differently. For instance,
> > one day we could handle jsonpath subscripts for jsonb. And for sure,
> > jsonpath subscripts are expected to be handled differently from text
> > subscripts. I see we can distinguish types during in prepare and
> > validate functions. But it seems there is no type information in
> > fetch and assign functions. Should we add something like this to the
> > SubscriptingRefState for future usage?
> >
> > Datum uppertypeoid[MAX_SUBSCRIPT_DEPTH];
> > Datum lowertypeoid[MAX_SUBSCRIPT_DEPTH];
>
> Yes, makes sense. My original idea was that it could be done within the
> jsonpath support patch itself, but at the same time providing these
> fields into SubscriptingRefState will help other potential extensions.
>
> Having said that, maybe it would be even better to introduce a field
> with an opaque structure for both SubscriptingRefState and
> SubscriptingRef, where every implementation of custom subscripting can
> store any necessary information? In case of jsonpath it could keep type
> information acquired in prepare function, which would be then passed via
> SubscriptingRefState down to the fetch/assign.

The idea of an opaque field in SubscriptingRef structure is more
attractive to me. Could you please implement it?

------
Regards,
Alexander Korotkov