The following code doesn't compile with gcc-4.3.2 (and gcc-4.4.0), and boost-1.36 (and boost-trunk of 2008/10/07) when using -std=c++0x on linux. #include int main() { boost::shared_mutex mtx; boost::upgrade_lockboost::shared_mutex lk(mtx); boost::upgrade_to_unique_lockboost::shared_mutex lk2(lk); } gcc spits: g++-4.4.0-alpha20081003 -std=c++0x -I src/boost-trunk teste.cpp -o teste In file included from src/boost-trunk/boost/thread/pthread/mutex.hpp:11, from src/boost-trunk/boost/thread/mutex.hpp:16, from src/boost-trunk/boost/thread/pthread/shared_mutex.hpp:12, from src/boost-trunk/boost/thread/shared_mutex.hpp:16, from teste.cpp:1: src/boost-trunk/boost/thread/locks.hpp: In destructor 'boost::upgrade_to_unique_lock<Mutex>::~upgrade_to_unique_lock() [with Mutex = boost::shared_mutex]': teste.cpp:8: instantiated from here src/boost-trunk/boost/thread/locks.hpp:807: error: no match for 'operator=' in '*((boost::upgrade_to_unique_lockboost::shared_mutex*)this)->boost::upgrade_to_unique_lockboost::shared_mutex::source = boost::move [with Mutex = boost::shared_mutex](((boost::unique_lockboost::shared_mutex&&)(&((boost::upgrade_to_unique_lockboost::shared_mutex*)this)->boost::upgrade_to_unique_lockboost::shared_mutex::exclusive)))' src/boost-trunk/boost/thread/locks.hpp:643: note: candidates are: boost::upgrade_lock<Mutex>& boost::upgrade_lock<Mutex>::operator=(boost::upgrade_lock<Mutex>&) [with Mutex = boost::shared_mutex] src/boost-trunk/boost/thread/locks.hpp:694: note: boost::upgrade_lock<Mutex>& boost::upgrade_lock<Mutex>::operator=(boost::detail::thread_move_t

) [with Mutex = boost::shared_mutex] src/boost-trunk/boost/thread/locks.hpp:701: note: boost::upgrade_lock<Mutex>& boost::upgrade_lock<Mutex>::operator=(boost::detail::thread_move_tboost::shared_mutex*)this)->boost::unique_lockboost::shared_mutex::m', which is of non-class type 'boost::shared_mutex*'

It compiles fine in non std++0x mode Regards, Rodolfo Lima