Re: array_ndims never returns zero

Vladimir Svedov <vodevsh@gmail.com> writes:
> Reading
> https://stackoverflow.com/questions/48022753/why-does-array-ndimsarray-produce-null#48022980
> confused me much - why array_ndims never returns zero indeed?..

Yeah, it's not a very good choice that it returns null for a zero-D
array.  But it's been like that for 20-some years, so the question
is whether we are prepared to take the compatibility hit from
changing it.

If we were willing to break things around zero-D arrays, I don't think
that's the only thing to change.  It's equally silly that array_dims()
returns NULL for such arrays, for instance; their dimensions are
certainly not unknown.  Perhaps an empty string is the right result,
though I've not thought about it hard.

I'd also argue that an out-of-range AARR_NDIM result is grounds
for raising an error; returning NULL is a poor substitute for
reporting data corruption.

In short, if we're to touch this, I'd want somebody to go through all
the array functions/operators and see if anything else is weird with
zero-D arrays.

            regards, tom lane