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

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

Maybe if you decide not to touch the code, I should report to documentation
mail group, asking to add this special exception to docs?..

Thank you

On 29 December 2017 at 19:50, Pavel Stehule <pavel.stehule@gmail.com> wrote: