Thread: array_ndims never returns zero
Hi,
so the question - do you think it makes sense?.. What is the logic behind it?
Reading https://stackoverflow.com/questions/48022753/why-does-array-ndimsarray-produce-null#48022980 confused me much - why array_ndims never returns zero indeed?..
select char_length('') returns zero and according to https://www.postgresql.org/docs/current/static/functions-string.html it shows the "Number of characters in string ",on the other hand https://www.postgresql.org/docs/10/static/functions-array.html array_ndims "returns the number of dimensions of the array",but https://github.com/postgres/postgres/blob/master/src/backend/utils/adt/arrayfuncs.c#L1635
| if (AARR_NDIM(v) <= 0 || AARR_NDIM(v) > MAXDIM) | |
| PG_RETURN_NULL(); |
Please advise where to address it if I chose the wrong channel, as It's probably not a bug, but a feature?..
Regards
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
regards, tom lane
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:
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#480229 80
> 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.RegardsPavel
regards, tom lane