Horton

Re: [HACKERS] [PATCH] Generic type subscripting

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>, 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: 2020-12-17T19:28:16Z
Lists: pgsql-hackers 
Pavel Stehule <pavel.stehule@gmail.com> writes:
> čt 17. 12. 2020 v 19:49 odesílatel Tom Lane <tgl@sss.pgh.pa.us> napsal:
>> So ... what's the problem with that?  Seems like what you should put
>> in and what you should get out should be the same type.

> I don't think so.  For  XML or JSON the target can be different, and it can
> safe one CAST

> DECLARE
>   n int;
>   v varchar;
>   js jsonb default '{"n": 100, "v" : "Hello"};
> BEGIN
>   n := js['n'];
>   v := js['v'];

If you're imagining that js['n'] and js['v'] would emit different
datatypes, forget it.  That would require knowing at parse time
what the structure of the json object will be at run time.

But in any case, the discussion here is about the source datatype
for an assignment, which this example doesn't even contain.

			regards, tom lane

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.