On Sep 29, 2006, at 9:14 AM, Tom Lane wrote:

[ expanding this thread, as it now needs wider discussion ]

"Paul B. Anderson" <[EMAIL PROTECTED]> writes:
Actually, I was not filling all of the arrays in sequential order.  I
added code to initialize them in order and the function seems to be
working now.  Is that a known problem?

Well, it's a documented behavior: section 8.10.4 saith

        A stored array value can be enlarged by assigning to an element
        adjacent to those already present, or by assigning to a slice
        that is adjacent to or overlaps the data already present.

Up to 8.2 we didn't have a lot of choice about this, because without any ability to have nulls embedded in arrays, there wasn't any sane thing to
do with the intermediate positions if you assigned to an element not
adjacent to the existing range. As of 8.2 we could allow assignment to
arbitrary positions by filling the intermediate positions with nulls.
The code hasn't actually been changed to allow that, but it's something
we could consider doing now.


At first blush, this strikes me as a bit too magical/implicit. Are there other languages where sequences behave similarly? The best analogy that comes to mind is sparse files, but in that case there is an implicit contract that the intervening empty regions do not actually occupy physical space, doesn't sound like that's true here.

I think the result of this change would be more difficult debugging of off-by-one errors and their ilk, rather than actually being a real benefit.

OTOH, perhaps there is a real use-case I am missing here. I don't see the rest of this thread on GENERAL and I couldn't find it searching the archives, where did it come from?


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