Hi Peter, The code here: http://lists.boost.org/boost-users/2005/05/11805.php appears to require the user to specify the root pointers in order to do a complete collection. This is in contrast to sp_collect.cpp which used Christopher's method [chri84] cited here: http://www.cs.kent.ac.uk/people/staff/rej/gcbib/gcbibC.html to find the roots, at least AFAICT. Is this intentional, or is the above code in 11805.php simply a sketch of a method which will eventually use something like Christopher's. I ask because some of the code in 11806.php appears similar to some in sp_collect.cpp. For example, I'm guessing that the map2_type in sp_collect corresponds to the map_type in reset_and_collect, i.e. the key is sorted on the referent, and the value is the number of smart_ptr's to that referent that are on the heap. Thanks for any clarification. -regards, Larry