35 class Maybe {
40   Maybe();
42   ~Maybe();
44   Maybe(const Maybe& rhs);
47   Maybe(const Maybe<U>& rhs);  // NOLINT(google-explicit-constructor)
49   Maybe(Maybe&& rhs) noexcept;
52   Maybe(Maybe<U>&& rhs);  // NOLINT(google-explicit-constructor)
54   Maybe& operator=(const Maybe& rhs);
57   Maybe& operator=(const Maybe<U>& rhs);
59   Maybe& operator=(Maybe&& rhs) noexcept;
62   Maybe& operator=(Maybe<U>&& rhs);
67   Maybe(const T& value);  // NOLINT(google-explicit-constructor)
72   Maybe(T&& value);  // NOLINT(google-explicit-constructor)
96   friend class Maybe;
99   Maybe& copy(const Maybe<U>& rhs);
102   Maybe& move(Maybe<U>&& rhs);
112 Maybe<T>::Maybe() : nothing_(true) {}  in Maybe()  function
115 Maybe<T>::~Maybe() {  in ~Maybe()
122 Maybe<T>::Maybe(const Maybe& rhs) : nothing_(rhs.nothing_) {  in Maybe()  function
130 Maybe<T>::Maybe(const Maybe<U>& rhs) : nothing_(rhs.nothing_) {  in Maybe()  function
137 Maybe<T>::Maybe(Maybe&& rhs) noexcept : nothing_(rhs.nothing_) {  in Maybe()  function
149 Maybe<T>::Maybe(Maybe<U>&& rhs) : nothing_(rhs.nothing_) {  in Maybe()  function
160 inline Maybe<T>& Maybe<T>::operator=(const Maybe& rhs) {
167 inline Maybe<T>& Maybe<T>::operator=(const Maybe<U>& rhs) {
173 Maybe<T>& Maybe<T>::copy(const Maybe<U>& rhs) {  in copy()
195 inline Maybe<T>& Maybe<T>::operator=(Maybe&& rhs) noexcept {
197   return move(std::forward<Maybe<T>>(rhs));
202 inline Maybe<T>& Maybe<T>::operator=(Maybe<U>&& rhs) {
203   return move(std::forward<Maybe<U>>(rhs));
208 Maybe<T>& Maybe<T>::move(Maybe<U>&& rhs) {  in move()
235 Maybe<T>::Maybe(const T& value) : nothing_(false) {  in Maybe()  function
240 Maybe<T>::Maybe(T&& value) : nothing_(false) {  in Maybe()  function
245 Maybe<T>::operator bool() const {
250 T& Maybe<T>::value() {  in value()
256 const T& Maybe<T>::value() const {  in value()
262 T Maybe<T>::value_or_default(const T& def) const {  in value_or_default()
270 void Maybe<T>::destroy() {  in destroy()
275 inline Maybe<typename std::remove_reference<T>::type> make_value(T&& value) {  in make_value()
276   return Maybe<typename std::remove_reference<T>::type>(std::forward<T>(value));  in make_value()
280 inline Maybe<T> make_nothing() {  in make_nothing()
281   return Maybe<T>();  in make_nothing()
288 typename std::enable_if<has_eq_op<T, U>::value, bool>::type operator==(const Maybe<T>& a,
289                                                                        const Maybe<U>& b) {
299 typename std::enable_if<has_eq_op<T, U>::value, bool>::type operator==(const Maybe<T>& a,
306 typename std::enable_if<has_eq_op<T, U>::value, bool>::type operator!=(const Maybe<T>& a,
307                                                                        const Maybe<U>& b) {
312 typename std::enable_if<has_lt_op<T, U>::value, bool>::type operator<(const Maybe<T>& a,
313                                                                       const Maybe<U>& b) {