boost::log::function_reference_wrapper — Reference wrapper for function objects.
// In header: <boost/log/utility/functional/fun_ref.hpp> template<typename FunT> struct function_reference_wrapper { // types typedef FunT::result_type result_type; // construct/copy/destruct explicit function_reference_wrapper(FunT &); // public member functions result_type operator()() const; template<typename... ArgsT> result_type operator()(ArgsT const &...) const; };