Re: Allow to specify #columns in heap/index_form_tuple

I wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
>> It'd be useful for FieldStore - we'd not have to error out anymore if
>> the number of columns changes (which I previously had "solved" by using
>> MaxHeapAttributeNumber sized values/nulls array).

> Ah, I see. But in that case you're not really truncating the tuple
> --- what you want is to be allowed to pass undersized datum/nulls
> arrays and have the missing columns be taken as nulls.

No, scratch that: you can't use an "extended" heap_form_tuple to solve
that problem, because it's not only the form-tuple end but the
deform-tuple end that needs fullsize arrays. Otherwise, we'd be losing
trailing-column values in the deform-and-reform cycle. So I still
don't see that there's a valid application for this feature.

regards, tom lane