63   template<class _Pair, class _Iter, class _Sent>
66     constructible_from<_Pair, _Iter, _Sent> &&
67     __convertible_to_non_slicing<_Iter, tuple_element_t<0, _Pair>> &&
72   template<input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent = _Iter,
73            subrange_kind _Kind = sized_sentinel_for<_Sent, _Iter>
76     requires (_Kind == subrange_kind::sized || !sized_sentinel_for<_Sent, _Iter>)
78     : public view_interface<subrange<_Iter, _Sent, _Kind>>
82 …c constexpr bool _StoreSize = (_Kind == subrange_kind::sized && !sized_sentinel_for<_Sent, _Iter>);
87     using _Size = conditional_t<_StoreSize, make_unsigned_t<iter_difference_t<_Iter>>, _Empty>;
88     _LIBCPP_NO_UNIQUE_ADDRESS _Iter __begin_ = _Iter();
94     subrange() requires default_initializable<_Iter> = default;
97     constexpr subrange(__convertible_to_non_slicing<_Iter> auto __iter, _Sent __sent)  in subrange()
103     constexpr subrange(__convertible_to_non_slicing<_Iter> auto __iter, _Sent __sent,  in subrange()
104                        make_unsigned_t<iter_difference_t<_Iter>> __n)  in subrange()
108       if constexpr (sized_sentinel_for<_Sent, _Iter>)  in subrange()
109         _LIBCPP_ASSERT((__end_ - __begin_) == static_cast<iter_difference_t<_Iter>>(__n),  in subrange()
115                __convertible_to_non_slicing<iterator_t<_Range>, _Iter> &&
125                __convertible_to_non_slicing<iterator_t<_Range>, _Iter> &&
134       requires __convertible_to_non_slicing<iterator_t<_Range>, _Iter> &&
137     constexpr subrange(_Range&& __range, make_unsigned_t<iter_difference_t<_Iter>> __n)  in subrange()
143       requires __pair_like_convertible_from<_Pair, const _Iter&, const _Sent&>
150     constexpr _Iter begin() const requires copyable<_Iter> {  in begin()
154     [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Iter begin() requires (!copyable<_Iter>) {  in begin()
168     constexpr make_unsigned_t<iter_difference_t<_Iter>> size() const  in size()
177 …[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr subrange next(iter_difference_t<_Iter> __n = 1) cons…
178       requires forward_iterator<_Iter>
185 … [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr subrange next(iter_difference_t<_Iter> __n = 1) && {
190 …[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr subrange prev(iter_difference_t<_Iter> __n = 1) const
191       requires bidirectional_iterator<_Iter>
199     constexpr subrange& advance(iter_difference_t<_Iter> __n) {  in advance()
200       if constexpr (bidirectional_iterator<_Iter>) {  in advance()
216   template<input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent>
217   subrange(_Iter, _Sent) -> subrange<_Iter, _Sent>;
219   template<input_or_output_iterator _Iter, sentinel_for<_Iter> _Sent>
220   subrange(_Iter, _Sent, make_unsigned_t<iter_difference_t<_Iter>>)
221     -> subrange<_Iter, _Sent, subrange_kind::sized>;
232   template<size_t _Index, class _Iter, class _Sent, subrange_kind _Kind>
233     requires ((_Index == 0 && copyable<_Iter>) || _Index == 1)
235   constexpr auto get(const subrange<_Iter, _Sent, _Kind>& __subrange) {  in get()  argument
242   template<size_t _Index, class _Iter, class _Sent, subrange_kind _Kind>
245   constexpr auto get(subrange<_Iter, _Sent, _Kind>&& __subrange) {  in get()  argument