Re: [HACKERS] [PATCH] Generic type subscripting

On Wed Jan 20, 2021 at 11:22 AM EST, Dmitry Dolgov wrote:
> > On Tue Jan 19, 2021 at 1:42 PM EST, Pavel Stehule wrote:
> >
> > I found minor issues.
> >
> > Doc - missing tag
> >
> > and three whitespaces issues
> >
> > see attached patch
>
> Thanks, I need to remember to not skipp doc building for testing process
> even for such small changes. Hope now I didn't forget anything.
>
> > On Wed, Jan 20, 2021 at 09:58:43AM -0500, Dian M Fay wrote:
>
> > Here's a full editing pass on the documentation, with v45 and Pavel's
> > doc-whitespaces-fix.patch applied. I also corrected a typo in one of the
> > added hints.
>
> Great! I've applied almost all of it, except:
>
> + A <type>jsonb</type> value will accept assignments to nonexistent
> subscript
> + paths as long as the nonexistent elements being traversed are all
> arrays.
>
> Maybe I've misunderstood the intention, but there is no requirement
> about arrays for creating such an empty path. I've formulated it as:
>
> + A <type>jsonb</type> value will accept assignments to nonexistent
> subscript
> + paths as long as the last existing path key is an object or an array.

My intention there was to highlight the difference between:

* SET obj['a']['b']['c'] = '"newvalue"'
* SET arr[0][0][3] = '"newvalue"'

obj has to conform to {"a": {"b": {...}}} in order to receive the
assignment of the nested c. If it doesn't, that's the error case we
discussed earlier. But arr can be null, [], and so on, and any missing
structure [[[null, null, null, "newvalue"]]] will be created. Take 2:

A <type>jsonb</type> value will accept assignments to nonexistent
subscript paths as long as object key subscripts can be traversed as
described above. The final subscript is not traversed and, if it
describes a missing object key, will be created. Nested arrays will
always be created and <literal>NULL</literal>-padded according to the
path until the value can be placed appropriately.