Re: [HACKERS] [PATCH] Generic type subscripting

From: Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
To: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Cc: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Steele <david(at)pgmasters(dot)net>, Nikita Glukhov <n(dot)gluhov(at)postgrespro(dot)ru>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Fetter <david(at)fetter(dot)org>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Oleksandr Shulgin <oleksandr(dot)shulgin(at)zalando(dot)de>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Oleg Bartunov <obartunov(at)gmail(dot)com>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] [PATCH] Generic type subscripting
Date: 2020-11-30 13:26:19
Message-ID: 20201130132619.zzgl272m5rcnhvzt@localhost
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> 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.

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