Re: strange behavior with C function and DEFAULT function parameters

On 10/20/2013 08:38 PM, Tomas Vondra wrote:
> Hi,
>
> I ran into some pretty strange behavior of C-language function and
> default parameter values, both on 9.2 and 9.4devel. Consider for example
> this trivial C function:
>
> Datum
> show_bug(PG_FUNCTION_ARGS) {
> elog(WARNING, "called ;-)");
> PG_RETURN_VOID();
> }
>
> which is accessed using this definition:
>
> CREATE FUNCTION show_bug(a TEXT DEFAULT NULL)
> RETURNS void
> AS 'bug.so'
> LANGUAGE C STRICT;
>
> and let's try various calls:
>
> db=# SELECT show_bug('a');
> WARNING: called ;-)
> show_bug
> ----------
>
> (1 row)
>
> Seems ok. Now let's use the default value:
>
> db=# SELECT show_bug();
> show_bug
> ----------
>
> (1 row)
>
> db=# SELECT show_bug(NULL);
> show_bug
> ----------
>
> (1 row)
>
> Well, seems quite strange to me - it seems as if the function is called,
> but apparently it's not. I can't find anything relevant in the docs.
>
> For comparison, a matching PL/pgSQL function:
>
> CREATE FUNCTION show_bug2(a TEXT DEFAULT NULL) RETURNS void AS $$
> BEGIN
> RAISE WARNING 'called ;-)';
> END;
> $$ LANGUAGE plpgsql;
>
> which behaves exactly as expected in all three cases:
>
> db=# SELECT show_bug('a');
> WARNING: called ;-)
> show_bug
> ----------
>
> (1 row)
>
> db=# SELECT show_bug();
> WARNING: called ;-)
> show_bug
> ----------
>
> (1 row)
> db=# SELECT show_bug(NULL);
> WARNING: called ;-)
> show_bug
> ----------
>
> (1 row)
>
> So, what I'm doing wrong? Seems like a bug to me ...
>

It's not a bug, it's expected. STRICT functions are not called with NULL
inputs - the result of the function is instead taken as NULL.

cheers

andrew