We don't really need NIL_IN_DICTIONARY, we only need NIL_IN_ARRAY. And the "array border" (or "high water mark") is the right word to solve the problem.
The idiom I would like to see makes #tab a valid L-value.
Then we could say:
tab = {1,2,3, [50] = 50}
#tab = 50
and ipairs would yield 1,2 ; 2,2 ; 3,3; 50,50.
This would be more attractive than the =tab.n= idiom we find ourselves settling on.
This new over-ride of #t should behave like the old #t, in that
tab[#tab + 1] = 51 -- #tab is now 51
tab[99] = 99 -- #tab is still 51
#tab = 99 -- and so on
Add a verb to table to do this in one call:
table.extend(tab, 99, "99") -- String is the rvalue
I don't get tripped up on sparse tables often, this would solve all the cases I've personally run into.
