assert(key in aa);
aa.remove(key);
So, as far as I can tell, the current situation is more efficient, and it
doesn't cost you any expressiveness. You can still have an exception thrown
when remove fails if you use enforce before the call if you want an exception
thrown when the element isn't there.
but then it should be called optional_remove - because it "mabye" removes
its like file_delete, DeleteFile (and all the others) on non existing
files - why is there an exception/error neeeded if missing?
the "maybe"-situation is not that often used in good code - because you
can't find your errors if many routines would work like remove
