43   template <typename F>
44   constexpr auto transform(F&& f) const& {  in transform()
45     using R = details::transform_result_t<F, decltype(value())>;  in transform()
46     if (has_value()) return R(std::invoke(std::forward<F>(f), value()));  in transform()
50   template <typename F>
51   constexpr auto transform(F&& f) & {  in transform()
52     using R = details::transform_result_t<F, decltype(value())>;  in transform()
53     if (has_value()) return R(std::invoke(std::forward<F>(f), value()));  in transform()
57   template <typename F>
58   constexpr auto transform(F&& f) const&& {  in transform()
59     using R = details::transform_result_t<F, decltype(std::move(value()))>;  in transform()
60     if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));  in transform()
64   template <typename F>
65   constexpr auto transform(F&& f) && {  in transform()
66     using R = details::transform_result_t<F, decltype(std::move(value()))>;  in transform()
67     if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));  in transform()
72   template <typename F>
73   constexpr auto and_then(F&& f) const& {  in and_then()
74     using R = details::and_then_result_t<F, decltype(value())>;  in and_then()
75     if (has_value()) return std::invoke(std::forward<F>(f), value());  in and_then()
79   template <typename F>
80   constexpr auto and_then(F&& f) & {  in and_then()
81     using R = details::and_then_result_t<F, decltype(value())>;  in and_then()
82     if (has_value()) return std::invoke(std::forward<F>(f), value());  in and_then()
86   template <typename F>
87   constexpr auto and_then(F&& f) const&& {  in and_then()
88     using R = details::and_then_result_t<F, decltype(std::move(value()))>;  in and_then()
89     if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));  in and_then()
93   template <typename F>
94   constexpr auto and_then(F&& f) && {  in and_then()
95     using R = details::and_then_result_t<F, decltype(std::move(value()))>;  in and_then()
96     if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));  in and_then()
101   template <typename F>
102   constexpr auto or_else(F&& f) const& -> details::or_else_result_t<F, T> {
104     return std::forward<F>(f)();
107   template <typename F>
108   constexpr auto or_else(F&& f) && -> details::or_else_result_t<F, T> {
110     return std::forward<F>(f)();