Re: proposal: fix corner use case of variadic fuctions usage

2013/1/23 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
>> what should be result of concat(variadic NULL::int[])
>> I enabled this use case, but what should be result?
>
> I think there are two somewhat defensible theories:
>
> (1) punt, and return NULL overall. So in this case the variadic
> function would act as if it were STRICT. That seems a bit weird though
> if the function is not strict otherwise.
>
> (2) Treat the NULL as if it were a zero-length array, giving rise to
> zero ordinary parameters. This could be problematic if the function
> can't cope very well with zero parameters ... but on the other hand,
> if it can't do so, then what will it do with VARIADIC '{}'::int[] ?

This is repeated question - how much is NULL ~ '{}'

There is only one precedent, I think

postgres=# select '>>>' || array_to_string('{}'::int[], '') || '<<<';
?column?
----------
>>><<<
(1 row)

postgres=# select '>>>' || array_to_string(NULL::int[], '') || '<<<';
?column?
----------

(1 row)

but this function is STRICT - so there is no precedent :(

>
> I lean a little bit towards (2) but it's definitely a judgment call.
> Anybody have any other arguments one way or the other?
>

> regards, tom lane