Re: Documentation Chapter 16: 8.21

On 2024-04-20 14:22 +0200, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/16/datatype-pseudo.html
> Description:
> 
> I tryed to implement a safe_cast function with 2 parameters and a return of
> type "any" but it failed. I get a syntax error, if I use "any" as a data
> type, because it is a sql function (similar to array contains) and not a
> data type.

You have to use a double-quoted identifier, i.e. "any" instead of ANY.
But it won't work with PL languages:

    => create function f() returns "any" as 'select 1' language sql;
    ERROR:  SQL functions cannot return type "any"

You have to code a C function for that.

> And if there is a data type "any" in postgres too, how should it work as
> parameter and wheres the difference to "anyelement"?

"any" is like "anyelement" just without the polymorphic[1] behavior.
So an argument of type "any" does not determine the result type for
"anyarray" as "anyelement" would.

[1] https://www.postgresql.org/docs/current/extend-type-system.html#EXTEND-TYPES-POLYMORPHIC

-- 
Erik