tl::expected

[grarup]

I'm trying to bind to a function that returns tl::expected, so I have create this.

	pybind11::class_<tl::expected<std::vector<std::string>, bifrost::Error>>(m, "expected_vector_string")
	    .def("has_value", &tl::expected<std::vector<std::string>, bifrost::Error>::has_value)
	    .def("value", &tl::expected<std::vector<std::string>, bifrost::Error>::value,
	         pybind11::return_value_policy::reference);

The has_value works fine but I can't get value or error to work.
this results in

robot/embedded/bifrost/pybind/bifrost_wrapper.cpp:57:7: error: no matching member function for call to 'def'
            .def("value", &tl::expected<std::vector<std::string>, bifrost::Error>::value,
            ~^~~
external/pybind11/include/pybind11/pybind11.h:1567:13: note: candidate template ignored: couldn't infer template argument 'Func'
    class_ &def(const char *name_, Func &&f, const Extra &...extra) {
            ^
external/pybind11/include/pybind11/pybind11.h:1592:13: note: candidate template ignored: substitution failure [with T = char[6]]: deduced incomplete pack <(no value), pybind11::return_value_policy> for template parameter 'Extra'
    class_ &def(const T &op, const Extra &...extra) {
            ^
external/pybind11/include/pybind11/pybind11.h:1604:13: note: candidate template ignored: could not match 'const detail::initimpl::constructor<Args...>' against 'const char[6]'
    class_ &def(const detail::initimpl::constructor<Args...> &init, const Extra &...extra) {
            ^
external/pybind11/include/pybind11/pybind11.h:1611:13: note: candidate template ignored: could not match 'const detail::initimpl::alias_constructor<Args...>' against 'const char[6]'
    class_ &def(const detail::initimpl::alias_constructor<Args...> &init, const Extra &...extra) {
            ^
external/pybind11/include/pybind11/pybind11.h:1618:13: note: candidate template ignored: could not match 'detail::initimpl::factory<Args...>' against 'const char[6]'
    class_ &def(detail::initimpl::factory<Args...> &&init, const Extra &...extra) {
            ^
external/pybind11/include/pybind11/pybind11.h:1624:13: note: candidate template ignored: could not match 'detail::initimpl::pickle_factory<Args...>' against 'const char[6]'
    class_ &def(detail::initimpl::pickle_factory<Args...> &&pf, const Extra &...extra) {