Assuming it's more efficient to use a struct to create many instances, what will cause the struct to get > removed when it's no longer needed? Will it cease to exist as soon as last > instance on which it's based ceases to exist?
Class and definestruct definitions never go away and there are no limits on how many you can have. The table of classes is access by index number (encoded into the class handle) so there is no performance hit with many classes. Of course, there would be a slight memory waste once you stopped using a class/definestruct, but it is not much, basically the length of all the field names plus a couple of dozen bytes overhead per class. It is more memory efficient to use a definestruct because, with makestruct, the variable names get encoded in the handle. So they would be included in every row variable.
