Re: Possible marginally-incompatible change to array subscripting

2015-12-22 18:34 GMT+01:00 Robert Haas <robertmhaas(at)gmail(dot)com>:

> 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].
>

exactly,

Pavel

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