32 template<class _Iter>
34   constructible_from<iter_value_t<_Iter>, iter_reference_t<_Iter>> &&
35   move_constructible<iter_value_t<_Iter>>;
37 template<input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent>
38   requires (!same_as<_Iter, _Sent> && copyable<_Iter>)
41     constexpr const iter_value_t<_Iter>* operator->() const noexcept {
44     iter_value_t<_Iter> __value_;
48     constexpr const iter_value_t<_Iter>& operator*() const noexcept {
51     iter_value_t<_Iter> __value_;
55   variant<_Iter, _Sent> __hold_;
57   common_iterator() requires default_initializable<_Iter> = default;
59   constexpr common_iterator(_Iter __i) : __hold_(in_place_type<_Iter>, _VSTD::move(__i)) {}  in common_iterator()
63     requires convertible_to<const _I2&, _Iter> && convertible_to<const _S2&, _Sent>
65     : __hold_([&]() -> variant<_Iter, _Sent> {  in common_iterator()
68         return variant<_Iter, _Sent>{in_place_index<0>, _VSTD::__unchecked_get<0>(__other.__hold_)};  in common_iterator()
69       return variant<_Iter, _Sent>{in_place_index<1>, _VSTD::__unchecked_get<1>(__other.__hold_)};  in common_iterator()
73     requires convertible_to<const _I2&, _Iter> && convertible_to<const _S2&, _Sent> &&
74              assignable_from<_Iter&, const _I2&> && assignable_from<_Sent&, const _S2&>
98 …_LIBCPP_ASSERT(holds_alternative<_Iter>(__hold_), "Attempted to dereference a non-dereferenceable …  in decltype()
99     return *_VSTD::__unchecked_get<_Iter>(__hold_);  in decltype()
103     requires __dereferenceable<const _Iter>  in decltype()
105 …_LIBCPP_ASSERT(holds_alternative<_Iter>(__hold_), "Attempted to dereference a non-dereferenceable …  in decltype()
106     return *_VSTD::__unchecked_get<_Iter>(__hold_);  in decltype()
109   template<class _I2 = _Iter>
116 …_LIBCPP_ASSERT(holds_alternative<_Iter>(__hold_), "Attempted to dereference a non-dereferenceable …
117     if constexpr (is_pointer_v<_Iter> || requires(const _Iter& __i) { __i.operator->(); })    {
118       return _VSTD::__unchecked_get<_Iter>(__hold_);
119     } else if constexpr (is_reference_v<iter_reference_t<_Iter>>) {
120       auto&& __tmp = *_VSTD::__unchecked_get<_Iter>(__hold_);
123       return __proxy{*_VSTD::__unchecked_get<_Iter>(__hold_)};
128 …_LIBCPP_ASSERT(holds_alternative<_Iter>(__hold_), "Attempted to increment a non-dereferenceable co…
129     ++_VSTD::__unchecked_get<_Iter>(__hold_); return *this;
133 …_LIBCPP_ASSERT(holds_alternative<_Iter>(__hold_), "Attempted to increment a non-dereferenceable co…
134     if constexpr (forward_iterator<_Iter>) {
138     } else if constexpr (requires (_Iter& __i) { { *__i++ } -> __can_reference; } ||
139                          !__can_use_postfix_proxy<_Iter>) {
140       return _VSTD::__unchecked_get<_Iter>(__hold_)++;
148   template<class _I2, sentinel_for<_Iter> _S2>
161       return _VSTD::__unchecked_get<_Iter>(__x.__hold_) == _VSTD::__unchecked_get<_S2>(__y.__hold_);
166   template<class _I2, sentinel_for<_Iter> _S2>
167     requires sentinel_for<_Sent, _I2> && equality_comparable_with<_Iter, _I2>
179 …   return  _VSTD::__unchecked_get<_Iter>(__x.__hold_) ==  _VSTD::__unchecked_get<_I2>(__y.__hold_);
182 …    return  _VSTD::__unchecked_get<_Iter>(__x.__hold_) == _VSTD::__unchecked_get<_S2>(__y.__hold_);
187   template<sized_sentinel_for<_Iter> _I2, sized_sentinel_for<_Iter> _S2>
200       return  _VSTD::__unchecked_get<_Iter>(__x.__hold_) - _VSTD::__unchecked_get<_I2>(__y.__hold_);
203       return  _VSTD::__unchecked_get<_Iter>(__x.__hold_) - _VSTD::__unchecked_get<_S2>(__y.__hold_);
208   friend constexpr iter_rvalue_reference_t<_Iter> iter_move(const common_iterator& __i)  in iter_move()
209     noexcept(noexcept(ranges::iter_move(declval<const _Iter&>())))  in iter_move()
210       requires input_iterator<_Iter>  in iter_move()
212 …_LIBCPP_ASSERT(holds_alternative<_Iter>(__i.__hold_), "Attempted to iter_move a non-dereferenceabl…  in iter_move()
213     return ranges::iter_move( _VSTD::__unchecked_get<_Iter>(__i.__hold_));  in iter_move()
216   template<indirectly_swappable<_Iter> _I2, class _S2>
218       noexcept(noexcept(ranges::iter_swap(declval<const _Iter&>(), declval<const _I2&>())))  in iter_swap()
220 …_LIBCPP_ASSERT(holds_alternative<_Iter>(__x.__hold_), "Attempted to iter_swap a non-dereferenceabl…  in iter_swap()
222 …return ranges::iter_swap(_VSTD::__unchecked_get<_Iter>(__x.__hold_), _VSTD::__unchecked_get<_I2>(_…  in iter_swap()
226 template<class _Iter, class _Sent>
227 struct incrementable_traits<common_iterator<_Iter, _Sent>> {
228   using difference_type = iter_difference_t<_Iter>;
231 template<class _Iter>
233   requires { typename iterator_traits<_Iter>::iterator_category; } &&
234   derived_from<typename iterator_traits<_Iter>::iterator_category, forward_iterator_tag>;
236 template<class _Iter, class _Sent>
237 concept __common_iter_has_ptr_op = requires(const common_iterator<_Iter, _Sent>& __a) {
246 template<class _Iter, class _Sent>
247   requires __common_iter_has_ptr_op<_Iter, _Sent>
248 struct __arrow_type_or_void<_Iter, _Sent> {
249     using type = decltype(declval<const common_iterator<_Iter, _Sent>&>().operator->());
252 template<input_iterator _Iter, class _Sent>
253 struct iterator_traits<common_iterator<_Iter, _Sent>> {
254   using iterator_concept = _If<forward_iterator<_Iter>,
257   using iterator_category = _If<__denotes_forward_iter<_Iter>,
260   using pointer = typename __arrow_type_or_void<_Iter, _Sent>::type;
261   using value_type = iter_value_t<_Iter>;
262   using difference_type = iter_difference_t<_Iter>;
263   using reference = iter_reference_t<_Iter>;