Re: Some questions about the array.

On Fri, Oct 9, 2015 at 6:27 PM, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:

> On 10/09/2015 08:02 AM, YUriy Zhuravlev wrote:
>
>> We were some of the issues associated with the behavior of arrays.
>> 1. We would like to implement arrays negative indices (from the end) like
>> in
>> Python or Ruby: arr[-2] or arr[1: -1]
>> but as an array can be indexed in the negative area so it probably can
>> not be
>> done.
>> 2. We would like to add the ability be omitted boundaries in the slice.
>> Example: arr[2:] or arr[:2]. But there was a problem with the update of an
>> empty array:
>> arr[1:][1:] = {1,2,3,4,5,6} can be interpreted as
>> arr[1:3][1:2] or arr[1:2] [1:3] or [1:1], [1:6]
>>
>> What is the history of the emergence of such arrays? Maybe something can
>> be
>> improved?
>>
>> P.S. I would like List datatype as in Python. Is there any fundamental
>> objections? Or we just did not have the time and enthusiasm before?
>> The current implementation I would call vectors or matrices but not
>> arrays.
>> IMHO
>>
>>
>>
> The name array is now far too baked in to change it.
>
> jsonb and json arrays have many of the characteristics you seem to want.
> They are always 0-based and negative indexes count from the end. They also
> don't have to be regular, unlike our native arrays.
>

jsonb and json arrays support very limited number of types. Casting other
datatypes to/from text is an option, but it is both awkward and not
space-compact.

Omitted boundaries in the slice looks nice for me. Considering problem with
empty array, current behaviour of empty array updating doesn't look
consistent for me.
When updating non-empty array its boundaries isn't extending. If one update
non-empty array out of its boundaries then he get an error "ERROR: array
subscript out of range".
If we extrapolate this logic to empty arrays then we this error should be
thrown on any update of empty array. Despite this, we allow any update of
empty array.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company