Re: array_ndims never returns zero

2017-12-29 17:52 GMT+01:00 Tom Lane <tgl@sss.pgh.pa.us>:

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.

Although I see a cost of compatibility break, I agree so NULL in this case is confusing.

The empty array can be taken as possible unlimited dimensional with zero sized dimensions.

The test on zero is more readable.

Regards

Pavel

                        regards, tom lane