What i'm trying to say is that in your business logic nil must not have any extra meaning beyond what Lua gives it ("there is no data here"). And in that meaning, if I write a buble-sorting library i expect arrays to be arrays, where every slot is data bound to be sorted. If i was supposed to support a mythical "array with holes", i would have to copy all the data to a proper array first! And if the nil actually get somehow sorted, then it's not a nil, but proper data, that better have an agreed upon meaning trough all the program and libraries... The motivation for storing nils in arrays is to give them a meaning they do not have in the language, and it will collide with someone else's use, sooner or later.
100% agree, which is why my original proposal was NOT to fiddle with nil in any way; it was to add an 'empty' value which would just behave like a normal value except only be equal to itself. Then your array would not have holes, it could sort normally (assuming 'empty' had a distinguished collating behavior) etc. And yes, these uses DO have a tendency to collide, which is why I suggested some attempt at a standard or convention was a good idea.
--Tim
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