Re: Allow any[] as input arguments for sql/plpgsql functions to mimic format()

Hi

po 22. 4. 2019 v 11:27 odesílatel Michał "phoe" Herda <phoe(at)disroot(dot)org>
napsal:

> Hey everyone,
>
> I am writing a plpgsql function that (to greatly simplify) raises an
> exception with a formatted* message. Ideally, I should be able to call
> it with raise_exception('The person %I has only %I bananas.', 'Fred',
> 8), which mimics the format(text, any[]) calling convention.
>
> Here is where I have encountered a limitation of PostgreSQL's design:
> https://www.postgresql.org/docs/11/datatype-pseudo.html mentions
> explicitly that, "At present most procedural languages forbid use of a
> pseudo-type as an argument type".
>
> My reasoning is that I should be able to accept a value of some type if
> all I do is passing it to a function that accepts exactly that type,
> such as format(text, any[]). Given the technical reality, I assume that
> I wouldn't be able to do anything else with that value, but that is
> fine, since I don't have to do anything with it regardless.
>
> BR
> Michał "phoe" Herda
>
> *I do not want to use the obvious solution of
> raise_exception(format(...)) because the argument to that function is
> the error ID that is then looked up in a table from which the error
> message and sqlstate are retrieved. My full code is in the attached SQL
> file. Once it is executed:
>
> SELECT gateway_error('user_does_not_exist', '2'); -- works but is
> unnatural,
> SELECT gateway_error('user_does_not_exist', 2); -- is natural but
> doesn't work.
>

It is known problem, and fix is not easy.

Any expressions inside plpgsql are simple queries like SELECT expr, and
they are executed same pipeline like queries.

The plans of these queries are stored and reused. Originally these plans
disallow any changes, now some changes are supported, but parameters should
be same all time. This is ensured by disallowing "any" type.

Other polymorphic types are very static, so there is not described risk.

Probably some enhancement can be in this are. The plan can be re-planed
after some change - but it can has lot of performance impacts. It is long
open topic. Some changes in direction to dynamic languages can increase
cost of some future optimization to higher performance :-(.

Regards

Pavel