If I turn on gcc's -Wextra option when compiling code that uses an accumulator with tag::max, I get a screen full of compiler warnings: [wheeler@cib: /var/tmp/acc] cat acc.cpp #include <iostream> #include #include #include using namespace boost::accumulators; int main() { accumulator_settag::max > acc; acc(1.2); acc(2.3); acc(3.4); acc(4.5); std::cout << "Max: " << max(acc) << std::endl; return 0; } [wheeler@cib: /var/tmp/acc] g++ -W -I /opt/ros/include/boost-1_37/ acc.cpp -o acc /opt/ros/include/boost-1_37/boost/concept_check.hpp: In instantiation of ‘boost::UnaryFunction, double, const double&>’: /opt/ros/include/boost-1_37/boost/concept/detail/has_constraints.hpp:40: instantiated from ‘const bool boost::concept::not_satisfied, double, const double&> >::value’ /opt/ros/include/boost-1_37/boost/concept/detail/has_constraints.hpp:43: instantiated from ‘boost::concept::not_satisfied, double, const double&> >’ /opt/ros/include/boost-1_37/boost/mpl/if.hpp:67: instantiated from ‘boost::mpl::if_, double, const double&> >, boost::concept::constraint, double, const double&> >, boost::concept::requirement, double, const double&> > >’ /opt/ros/include/boost-1_37/boost/concept/detail/general.hpp:19: instantiated from ‘boost::concept::requirement_, double, const double&>)>’ /opt/ros/include/boost-1_37/boost/accumulators/numeric/detail/function1.hpp:67: instantiated from ‘typename boost::detail::function1<F>::result::type boost::detail::function1<F>::operator()(const A0&) const [with A0 = double, F = boost::numeric::functional::as_min, boost::numeric::functional::tag > >]’ /opt/ros/include/boost-1_37/boost/accumulators/statistics/max.hpp:36: instantiated from ‘boost::accumulators::impl::max_impl<Sample>::max_impl(const Args&) [with Args = boost::parameter::aux::arg_list, void> >, boost::parameter::aux::empty_arg_list>, Sample = double]’ /opt/ros/include/boost-1_37/boost/accumulators/framework/depends_on.hpp:282: instantiated from ‘boost::accumulators::detail::accumulator_wrapper::accumulator_wrapper(const Args&) [with Args = boost::parameter::aux::arg_list, void> >, boost::parameter::aux::empty_arg_list>, Accumulator = boost::accumulators::impl::max_impl<double>, Feature = boost::accumulators::tag::max]’ /opt/ros/include/boost-1_37/boost/accumulators/framework/depends_on.hpp:215: instantiated from ‘static boost::fusion::cons::value>::type> boost::accumulators::detail::build_acc_list::call(const Args&, const First&, const Last&) [with Args = boost::parameter::aux::arg_list, void> >, boost::parameter::aux::empty_arg_list>, First = boost::fusion::mpl_iterator, boost::mpl::vector0, 0>, 0l> >, Last = boost::fusion::mpl_iterator, boost::mpl::vector0, 0>, 1l> >]’ /opt/ros/include/boost-1_37/boost/accumulators/framework/depends_on.hpp:234: instantiated from ‘typename boost::accumulators::detail::meta::make_acc_list<Sequence>::type boost::accumulators::detail::make_acc_list(const Sequence&, const Args&) [with Sequence = boost::mpl::v_item, boost::mpl::vector0, 0>, Args = boost::parameter::aux::arg_list, void> >, boost::parameter::aux::empty_arg_list>]’ /opt/ros/include/boost-1_37/boost/accumulators/framework/accumulator_set.hpp:145: instantiated from ‘boost::accumulators::accumulator_set::accumulator_set() [with Sample = double, Features = boost::accumulators::stats, Weight = void]’ acc.cpp:9: instantiated from here /opt/ros/include/boost-1_37/boost/concept_check.hpp:325: warning: non-static reference ‘const double& boost::UnaryFunction, double, const double&>::arg’ in class without a constructor