Re: [HACKERS] [PATCH] Generic type subscripting

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От Dmitry Dolgov
Тема Re: [HACKERS] [PATCH] Generic type subscripting
Дата
Msg-id CA+q6zcULY8b37PV=G+efOP04UnHksxcJjjKe2OoA+NmrHMupKQ@mail.gmail.com
обсуждение исходный текст
Ответ на Re: [HACKERS] [PATCH] Generic type subscripting  (Arthur Zakirov <a.zakirov@postgrespro.ru>)
Ответы Re: [HACKERS] [PATCH] Generic type subscripting  (Tom Lane <tgl@sss.pgh.pa.us>)
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> On 9 September 2017 at 23:33, Arthur Zakirov <a.zakirov@postgrespro.ru> wrote:
> PostgreSQL and documentation with the patch compiles without any errors. All
> regression tests passed.

Thank you!

> But honestly I still cannot say that I agree with *_extract() and *_assign()
> functions creation way. For example, there is no entry in pg_depend for them
> ...
> =# drop function custom_subscripting_extract(internal);
> =# select data[0] from test_subscripting;
> ERROR:  function 0x55deb7911bfd returned NULL

Hm...I never thought about the feature in this way. When I was experimenting I
also tried another approach for this - save to `refevalfunc` a function
pointer to an appropriate function. For simple situations it was ok, but there
were questions about how it would work with node-related functions from
`outfuncs`/`copyfuncs` etc. Another my idea was to find out an actual
`refevalfunc` not at the time of a node creation but later on - this was also
questionable since in this case we need to carry a lot of information with a node
just for this sole purpose. Maybe you can suggest something else?

About dependencies between functions - as far as I understand one cannot create
a `pg_depend` entry or any other kind of dependencies between custom
user-defined functions. So yes, looks like with the current approach the only
solution would be to check in the `_parse` function that `_extract` and
`_assign` functions are existed (which is inconvenient).

> For example, there is no entry in pg_depend

Are there any other disadvantages of this approach?

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