- (self.last_add[#self.last_add] or self):add_direct_child(s);
- t_insert(self.last_add, s);
+ local last_add = self.last_add;
+ if not last_add then last_add = {}; self.last_add = last_add; end
+ (last_add[#last_add] or self):add_direct_child(s);
+ t_insert(last_add, s);