fcppt::optional::reference< int const > optional_int_ref; int_vector const empty{}; CHECK_FALSE( fcppt::container::maybe_front( empty ).has_value() ); int_vector const vec12{ 1, 2 }; CHECK( fcppt::container::maybe_front( vec12 ) == optional_int_ref( fcppt::make_cref( vec12.front() ) ) ); }