[boost] program_options and optional

Seems natural to use boost::optional with program_options. Has anyone tried this? For example, consider this: int main (int argc, char** argv) { namespace po = boost::program_options; optional<double> x; po::options_description desc("Allowed options"); desc.add_options() ("help", "produce help message") ("x", po::value<double>()->notifier (var(x)=_1)) ; To set the optional<double> x, this uses boost::lambda. Is there a more direct approach?