I'm trying to figure out a good way to extend an Array, when the items 
may not be added in index order, and I don't know the final highest 
index.  Does anyone have any suggestions?

What occurs to me is that I could double the length of the array 
whenever I want to add more than one element by doing something like:
a    =    a    + Array.new(a.length)
Naturally, it would need to be a bit more complicated, as, e.g., I'd 
need to ensure that the resulting array actually *would* hold the 
proposed index.  Still, something only a little more complicated should 
_work_, but is that the best approach?