Horton

Re: [HACKERS] [PATCH] Generic type subscripting

Dmitry Dolgov <9erthalion6@gmail.com>

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From: Dmitry Dolgov <9erthalion6@gmail.com>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Alexander Korotkov <aekorotkov@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, David Steele <david@pgmasters.net>, Nikita Glukhov <n.gluhov@postgrespro.ru>, Alvaro Herrera <alvherre@2ndquadrant.com>, David Fetter <david@fetter.org>, Thomas Munro <thomas.munro@gmail.com>, Oleksandr Shulgin <oleksandr.shulgin@zalando.de>, Robert Haas <robertmhaas@gmail.com>, Michael Paquier <michael.paquier@gmail.com>, Oleg Bartunov <obartunov@gmail.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-12-11T15:19:57Z
Lists: pgsql-hackers 
> On Wed, Dec 09, 2020 at 04:59:34PM -0500, Tom Lane wrote:
>
> 0001 adds the ability to attach a subscript handler to an existing
> data type with ALTER TYPE.  This is clearly going to be necessary
> if we want extension types to be able to use this facility.  The
> only thing that I think might be controversial here is that I did
> not add the ability to set pg_type.typelem.  While that'd be easy
> enough so far as ALTER TYPE is concerned, I'm not sure that we want
> to encourage people to change it.  The dependency rules mean that
> the semantics of typelem aren't something you really want to change
> after-the-fact on an existing type.  Also, if we did allow it, any
> existing SubscriptingRef.refelemtype values in stored views would
> fail to be updated.

I'm curious what could be the use case for setting pg_type.typelem for
subscripting? I don't see this that much controversial, but maybe I'm
missing something.

> On Thu, Dec 10, 2020 at 05:37:20AM +0100, Pavel Stehule wrote:
> st 9. 12. 2020 v 22:59 odesílatel Tom Lane <tgl@sss.pgh.pa.us> napsal:
>
> > 0002 makes use of that to support subscripting of hstore.  I'm not
> > sure how much we care about that from a functionality standpoint,
> > but it seems like it might be good to have a contrib module testing
> > that extensions can use this.  Also, I thought possibly an example
> > showing what's basically the minimum possible amount of complexity
> > would be good to have.  If people like this, I'll finish it up (it
> > lacks docs) and add it.
> >
>
> +1 using subscripts for hstore is nice idea

Yeah, I also find it's a good suggestion, the implementation seems fine
as well. As a side note, I'm surprised hstore doesn't have any
functionality to update values, except hstore_concat.

Commits

  1. Throw error when assigning jsonb scalar instead of a composite object

  2. Filling array gaps during jsonb subscripting

  3. Implementation of subscripting for jsonb

  4. Allow ALTER TYPE to update an existing type's typsubscript value.

  5. Allow subscripting of hstore values.

  6. Support subscripting of arbitrary types, not only arrays.

  7. jit: Reference function pointer types via llvmjit_types.c.

  8. Teach contain_leaked_vars that assignment SubscriptingRefs are leaky.

  9. jit: Correct parameter type for generated expression evaluation functions.

  10. Renaming for new subscripting mechanism

  11. Fix assertion failure for SSL connections.

  12. Teach eval_const_expressions() to handle some more cases.