Re: Possible marginally-incompatible change to array subscripting

On Tue, Dec 22, 2015 at 11:51 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I'm reviewing Yury Zhuravlev's patch to allow array slice boundaries to be
> omitted, for example "a[4:]" means "the slice extending from element 4 to
> the last element of a". It strikes me that there's an improvement we
> could easily make for the case where a mixture of slice and non-slice
> syntax appears, that is something like "a[3:4][5]". Now, this has always
> meant a slice, and the way we've traditionally managed that is to treat
> simple subscripts as being the range upper bound with a lower bound of 1;
> that is, what this example means is exactly "a[3:4][1:5]".
>
> ISTM that if we'd had Yury's code in there from the beginning, what we
> would define this as meaning is "a[3:4][:5]", ie the implied range runs
> from whatever the array lower bound is up to the specified subscript.
>
> This would make no difference of course for the common case where the
> array lower bound is 1, but it seems a lot less arbitrary when it isn't.
> So I think we should strongly consider changing it to mean that, even
> though it would be non-backwards-compatible in such cases.
>
> Comments?

Gosh, our arrays are strange. I would have expected a[3:4][5] to mean
a[3:4][5:5].

--
Robert Haas
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