Re: [HACKERS] [PATCH] Generic type subscripting

> 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?