Hi Peter, Just a thought: perhaps this constructor: explicit shared_ptr(weak_ptr<Y> const & r); should be private, and the only way to create a shared_ptr from a weak_ptr is: shared_ptr<T> val = weak->lock(); This way, the shared_ptr public constructors will never throw. Users will not make mistakes like this: shared_ptr<T> val = weak; I'm saying this, because I just made this mistake a few hours ago... After a while, the shared_ptr<> constructor started to throw at me ;) Best, John -- John Torjo, Contributing editor, C/C++ Users Journal -- "Win32 GUI Generics" -- generics & GUI do mix, after all -- http://www.torjo.com/win32gui/ -- v1.5 - tooltips at your fingertips (work for menus too!) + bitmap buttons (work for MessageBox too!) + tab dialogs, hyper links, lite html