Re: [HACKERS] [PATCH] Generic type subscripting

> On Mon, Nov 30, 2020 at 04:12:29PM +0300, Alexander Korotkov wrote:
>
> > > 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?

Sure, doesn't seem to be that much work.