Such a class is already in Boost, in two places: /home/wash/development/boost-trunk-wc/boost/range/detail/safe_bool.hpp /home/wash/development/boost-trunk-wc/boost/spirit/core/safe_bool.hpp /home/wash/development/boost-trunk-wc/boost/spirit/home/classic/core/safe_bool.hpp /home/wash/development/boost-trunk-wc/boost/spirit/include/classic_safe_bool.hpp smart_ptr also has a version. Attached is a modified version of this that incorporates portability code from the smart_ptr version into the variant of the spirit safe_bool that Hartmut and I use at work. I like to have a macro for this, so I have an operator that's convertible to the safe_bool class, which is itself convertible to bool (this avoids problem with the need for "typename" in the macro in certain contexts). The safe_bool class is itself convertible to bool. Feel free to incorporate any of this code into whatever comes out of this thread. -- Bryce Lelbach aka wash boost-spirit.com px.cct.lsu.edu github.com/lll-project