20 #include <boost/optional.hpp>
28 using std::make_optional;
31 using std::bad_optional_access;
35 using boost::optional;
36 using boost::make_optional;
37 using boost::bad_optional_access;
38 using nullopt_t = boost::none_t;
41 static const boost::none_t nullopt{boost::none_t::init_tag{}};