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lib/libcxx/include/iterator (32601B) - Raw


      1 // -*- C++ -*-
      2 //===----------------------------------------------------------------------===//
      3 //
      4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
      5 // See https://llvm.org/LICENSE.txt for license information.
      6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #ifndef _LIBCPP_ITERATOR
     11 #define _LIBCPP_ITERATOR
     12 
     13 /*
     14     iterator synopsis
     15 
     16 #include <concepts>
     17 
     18 namespace std
     19 {
     20 template<class> struct incrementable_traits;       // since C++20
     21 template<class T>
     22   using iter_difference_t = see below;             // since C++20
     23 
     24 template<class> struct indirectly_readable_traits; // since C++20
     25 template<class T>
     26   using iter_value_t = see below;                  // since C++20
     27 
     28 template<class Iterator>
     29 struct iterator_traits;
     30 
     31 template<class T>
     32   requires is_object_v<T>                    // since C++20
     33 struct iterator_traits<T*>;
     34 
     35 template<dereferenceable T>
     36   using iter_reference_t = decltype(*declval<T&>());
     37 
     38 namespace ranges::inline unspecified {
     39     inline constexpr unspecified iter_move = unspecified; // since C++20, nodiscard as an extension
     40 }}
     41 
     42 template<dereferenceable T>
     43   requires ...
     44 using iter_rvalue_reference_t = decltype(ranges::iter_move(declval<T&>())); // since C++20
     45 
     46 // [iterator.concepts], iterator concepts
     47 // [iterator.concept.readable], concept indirectly_readable
     48 template<class In>
     49   concept indirectly_readable = see below;                      // since C++20
     50 
     51 template<indirectly_readable T>
     52   using iter_common_reference_t =
     53     common_reference_t<iter_reference_t<T>, iter_value_t<T>&>;  // since C++20
     54 
     55 // [iterator.concept.writable], concept indirectly_writable
     56 template<class Out, class T>
     57   concept indirectly_writable = see below;                // since C++20
     58 
     59 // [iterator.concept.winc], concept weakly_incrementable
     60 template<class I>
     61   concept weakly_incrementable = see below;                // since C++20
     62 
     63 // [iterator.concept.inc], concept incrementable
     64 template<class I>
     65   concept incrementable = see below;                       // since C++20
     66 
     67 // [iterator.concept.iterator], concept input_or_output_iterator
     68   template<class I>
     69     concept input_or_output_iterator = see below;          // since C++20
     70 
     71 // [iterator.concept.sentinel], concept sentinel_for
     72 template<class S, class I>
     73   concept sentinel_for = see below;                        // since C++20
     74 
     75 // [iterator.concept.sizedsentinel], concept sized_sentinel_for
     76 template<class S, class I>
     77   inline constexpr bool disable_sized_sentinel_for = false;
     78 
     79 template<class S, class I>
     80   concept sized_sentinel_for = see below;
     81 
     82 // [iterator.concept.input], concept input_iterator
     83 template<class I>
     84   concept input_iterator = see below;                      // since C++20
     85 
     86 // [iterator.concept.output], concept output_iterator
     87 template<class I, class T>
     88   concept output_iterator = see below;                     // since C++20
     89 
     90 // [iterator.concept.forward], concept forward_iterator
     91 template<class I>
     92   concept forward_iterator = see below;                    // since C++20
     93 
     94 // [iterator.concept.bidir], concept bidirectional_iterator
     95 template<class I>
     96   concept bidirectional_iterator = see below;              // since C++20
     97 
     98 // [iterator.concept.random.access], concept random_access_iterator
     99 template<class I>
    100   concept random_access_iterator = see below;              // since C++20
    101 
    102 // [indirectcallable]
    103 // [indirectcallable.indirectinvocable]
    104 template<class F, class I>
    105   concept indirectly_unary_invocable = see below;          // since C++20
    106 
    107 template<class F, class I>
    108   concept indirectly_regular_unary_invocable = see below;  // since C++20
    109 
    110 template<class F, class I>
    111   concept indirect_unary_predicate = see below;            // since C++20
    112 
    113 template<class F, class I1, class I2>
    114   concept indirect_binary_predicate = see below;           // since C++20
    115 
    116 template<class F, class I1, class I2 = I1>
    117   concept indirect_equivalence_relation = see below;       // since C++20
    118 
    119 template<class F, class I1, class I2 = I1>
    120   concept indirect_strict_weak_order = see below;          // since C++20
    121 
    122 template<class F, class... Is>
    123   using indirect_result_t = see below;                     // since C++20
    124 
    125 // [projected], projected
    126 template<indirectly_readable I, indirectly_regular_unary_invocable<I> Proj>
    127   struct projected;                                        // since C++20
    128 
    129 template<weakly_incrementable I, indirectly_regular_unary_invocable<I> Proj>
    130   struct incrementable_traits<projected<I, Proj>>;         // since C++20
    131 
    132 // [alg.req.ind.move], concept indirectly_movable
    133 template<class In, class Out>
    134   concept indirectly_movable = see below;                  // since C++20
    135 
    136 template<class In, class Out>
    137   concept indirectly_movable_storable = see below;         // since C++20
    138 
    139 // [alg.req.ind.copy], concept indirectly_copyable
    140 template<class In, class Out>
    141   concept indirectly_copyable = see below;                 // since C++20
    142 
    143 template<class In, class Out>
    144   concept indirectly_copyable_storable = see below;        // since C++20
    145 
    146 // [alg.req.ind.swap], concept indirectly_swappable
    147 template<class I1, class I2 = I1>
    148   concept indirectly_swappable = see below;                // since C++20
    149 
    150 template<class I1, class I2, class R, class P1 = identity,
    151          class P2 = identity>
    152   concept indirectly_comparable =
    153     indirect_binary_predicate<R, projected<I1, P1>, projected<I2, P2>>; // since C++20
    154 
    155 // [alg.req.permutable], concept permutable
    156 template<class I>
    157   concept permutable = see below;                          // since C++20
    158 
    159  // [alg.req.mergeable], concept mergeable
    160 template<class I1, class I2, class Out,
    161     class R = ranges::less, class P1 = identity, class P2 = identity>
    162   concept mergeable = see below;                           // since C++20
    163 
    164 // [alg.req.sortable], concept sortable
    165 template<class I, class R = ranges::less, class P = identity>
    166   concept sortable = see below;                            // since C++20
    167 
    168 template<input_or_output_iterator I, sentinel_for<I> S>
    169   requires (!same_as<I, S> && copyable<I>)
    170 class common_iterator;                                     // since C++20
    171 
    172 template<class Category, class T, class Distance = ptrdiff_t,
    173          class Pointer = T*, class Reference = T&>
    174 struct iterator                                            // deprecated in C++17
    175 {
    176     typedef T         value_type;
    177     typedef Distance  difference_type;
    178     typedef Pointer   pointer;
    179     typedef Reference reference;
    180     typedef Category  iterator_category;
    181 };
    182 
    183 struct input_iterator_tag  {};
    184 struct output_iterator_tag {};
    185 struct forward_iterator_tag       : public input_iterator_tag         {};
    186 struct bidirectional_iterator_tag : public forward_iterator_tag       {};
    187 struct random_access_iterator_tag : public bidirectional_iterator_tag {};
    188 struct contiguous_iterator_tag    : public random_access_iterator_tag {};
    189 
    190 // 27.4.3, iterator operations
    191 template <class InputIterator, class Distance>  // constexpr in C++17
    192   constexpr void advance(InputIterator& i, Distance n);
    193 
    194 template <class InputIterator>  // constexpr in C++17
    195   constexpr typename iterator_traits<InputIterator>::difference_type
    196     distance(InputIterator first, InputIterator last);
    197 
    198 template <class InputIterator>  // constexpr in C++17
    199   constexpr InputIterator next(InputIterator x,
    200 typename iterator_traits<InputIterator>::difference_type n = 1);
    201 
    202 template <class BidirectionalIterator>  // constexpr in C++17
    203   constexpr BidirectionalIterator prev(BidirectionalIterator x,
    204     typename iterator_traits<BidirectionalIterator>::difference_type n = 1);
    205 
    206 // [range.iter.ops], range iterator operations
    207 namespace ranges {
    208   // [range.iter.op.advance], ranges::advance
    209   template<input_or_output_iterator I>
    210     constexpr void advance(I& i, iter_difference_t<I> n);                          // since C++20
    211   template<input_or_output_iterator I, sentinel_for<I> S>
    212     constexpr void advance(I& i, S bound);                                         // since C++20
    213   template<input_or_output_iterator I, sentinel_for<I> S>
    214     constexpr iter_difference_t<I> advance(I& i, iter_difference_t<I> n, S bound); // since C++20
    215 }
    216 
    217 template <class Iterator>
    218 class reverse_iterator
    219     : public iterator<typename iterator_traits<Iterator>::iterator_category, // until C++17
    220                       typename iterator_traits<Iterator>::value_type,
    221                       typename iterator_traits<Iterator>::difference_type,
    222                       typename iterator_traits<Iterator>::pointer,
    223                       typename iterator_traits<Iterator>::reference>
    224 {
    225 protected:
    226     Iterator current;
    227 public:
    228     using iterator_type     = Iterator;
    229     using iterator_concept  = see below; // since C++20
    230     using iterator_category = typename iterator_traits<Iterator>::iterator_category; // since C++17, until C++20
    231     using iterator_category = see below; // since C++20
    232     using value_type        = typename iterator_traits<Iterator>::value_type; // since C++17, until C++20
    233     using value_type        = iter_value_t<Iterator>; // since C++20
    234     using difference_type   = typename iterator_traits<Iterator>::difference_type; // until C++20
    235     using difference_type   = iter_difference_t<Iterator>; // since C++20
    236     using pointer           = typename iterator_traits<Iterator>::pointer;
    237     using reference         = typename iterator_traits<Iterator>::reference; // until C++20
    238     using reference         = iter_reference_t<Iterator>; // since C++20
    239 
    240     constexpr reverse_iterator();
    241     constexpr explicit reverse_iterator(Iterator x);
    242     template <class U> constexpr reverse_iterator(const reverse_iterator<U>& u);
    243     template <class U> constexpr reverse_iterator& operator=(const reverse_iterator<U>& u);
    244     constexpr Iterator base() const;
    245     constexpr reference operator*() const;
    246     constexpr pointer   operator->() const; // until C++20
    247     constexpr pointer   operator->() const requires see below; // since C++20
    248     constexpr reverse_iterator& operator++();
    249     constexpr reverse_iterator  operator++(int);
    250     constexpr reverse_iterator& operator--();
    251     constexpr reverse_iterator  operator--(int);
    252     constexpr reverse_iterator  operator+ (difference_type n) const;
    253     constexpr reverse_iterator& operator+=(difference_type n);
    254     constexpr reverse_iterator  operator- (difference_type n) const;
    255     constexpr reverse_iterator& operator-=(difference_type n);
    256     constexpr unspecified       operator[](difference_type n) const;
    257 
    258     friend constexpr iter_rvalue_reference_t<Iterator>
    259       iter_move(const reverse_iterator& i) noexcept(see below);
    260     template<indirectly_swappable<Iterator> Iterator2>
    261       friend constexpr void
    262         iter_swap(const reverse_iterator& x,
    263                   const reverse_iterator<Iterator2>& y) noexcept(see below);
    264 };
    265 
    266 template <class Iterator1, class Iterator2>
    267 constexpr bool                          // constexpr in C++17
    268 operator==(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
    269 
    270 template <class Iterator1, class Iterator2>
    271 constexpr bool                          // constexpr in C++17
    272 operator!=(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
    273 
    274 template <class Iterator1, class Iterator2>
    275 constexpr bool                          // constexpr in C++17
    276 operator<(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
    277 
    278 template <class Iterator1, class Iterator2>
    279 constexpr bool                          // constexpr in C++17
    280 operator>(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
    281 
    282 template <class Iterator1, class Iterator2>
    283 constexpr bool                          // constexpr in C++17
    284 operator<=(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
    285 
    286 template <class Iterator1, class Iterator2>
    287 constexpr bool                          // constexpr in C++17
    288 operator>=(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);
    289 
    290 template<class Iterator1, three_way_comparable_with<Iterator1> Iterator2>
    291   constexpr compare_three_way_result_t<Iterator1, Iterator2>
    292     operator<=>(const reverse_iterator<Iterator1>& x,
    293                 const reverse_iterator<Iterator2>& y);
    294 
    295 template <class Iterator1, class Iterator2>
    296 constexpr auto
    297 operator-(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y)
    298 -> decltype(__y.base() - __x.base());   // constexpr in C++17
    299 
    300 template <class Iterator>
    301 constexpr reverse_iterator<Iterator>
    302 operator+(typename reverse_iterator<Iterator>::difference_type n,
    303           const reverse_iterator<Iterator>& x);   // constexpr in C++17
    304 
    305 template <class Iterator>
    306 constexpr reverse_iterator<Iterator> make_reverse_iterator(Iterator i); // C++14, constexpr in C++17
    307 
    308 template<class Iterator1, class Iterator2>
    309     requires (!sized_sentinel_for<Iterator1, Iterator2>)
    310   inline constexpr bool disable_sized_sentinel_for<reverse_iterator<Iterator1>,
    311                                                    reverse_iterator<Iterator2>> = true;
    312 
    313 template <class Container>
    314 class back_insert_iterator
    315     : public iterator<output_iterator_tag, void, void, void, void> // until C++17
    316 {
    317 protected:
    318     Container* container;
    319 public:
    320     typedef Container                   container_type;
    321     typedef void                        value_type;
    322     typedef void                        difference_type; // until C++20
    323     typedef ptrdiff_t                   difference_type; // since C++20
    324     typedef void                        reference;
    325     typedef void                        pointer;
    326 
    327     explicit back_insert_iterator(Container& x);  // constexpr in C++20
    328     back_insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
    329     back_insert_iterator& operator*();  // constexpr in C++20
    330     back_insert_iterator& operator++();  // constexpr in C++20
    331     back_insert_iterator  operator++(int);  // constexpr in C++20
    332 };
    333 
    334 template <class Container> back_insert_iterator<Container> back_inserter(Container& x);  // constexpr in C++20
    335 
    336 template <class Container>
    337 class front_insert_iterator
    338     : public iterator<output_iterator_tag, void, void, void, void> // until C++17
    339 {
    340 protected:
    341     Container* container;
    342 public:
    343     typedef Container                    container_type;
    344     typedef void                         value_type;
    345     typedef void                         difference_type; // until C++20
    346     typedef ptrdiff_t                    difference_type; // since C++20
    347     typedef void                         reference;
    348     typedef void                         pointer;
    349 
    350     explicit front_insert_iterator(Container& x);  // constexpr in C++20
    351     front_insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
    352     front_insert_iterator& operator*();  // constexpr in C++20
    353     front_insert_iterator& operator++();  // constexpr in C++20
    354     front_insert_iterator  operator++(int);  // constexpr in C++20
    355 };
    356 
    357 template <class Container> front_insert_iterator<Container> front_inserter(Container& x);  // constexpr in C++20
    358 
    359 template <class Container>
    360 class insert_iterator
    361     : public iterator<output_iterator_tag, void, void, void, void> // until C++17
    362 {
    363 protected:
    364     Container* container;
    365     typename Container::iterator iter;
    366 public:
    367     typedef Container              container_type;
    368     typedef void                   value_type;
    369     typedef void                   difference_type; // until C++20
    370     typedef ptrdiff_t              difference_type; // since C++20
    371     typedef void                   reference;
    372     typedef void                   pointer;
    373 
    374     insert_iterator(Container& x, typename Container::iterator i);  // constexpr in C++20
    375     insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
    376     insert_iterator& operator*();  // constexpr in C++20
    377     insert_iterator& operator++();  // constexpr in C++20
    378     insert_iterator& operator++(int);  // constexpr in C++20
    379 };
    380 
    381 template <class Container>
    382 insert_iterator<Container> inserter(Container& x, typename Container::iterator i);  // until C++20
    383 template <class Container>
    384 constexpr insert_iterator<Container> inserter(Container& x, ranges::iterator_t<Container> i);  // since C++20
    385 
    386 template <class Iterator>
    387 class move_iterator {
    388 public:
    389     using iterator_type     = Iterator;
    390     using iterator_concept  = see below; // From C++20
    391     using iterator_category = see below; // not always present starting from C++20
    392     using value_type        = iter_value_t<Iterator>; // Until C++20, iterator_traits<Iterator>::value_type
    393     using difference_type   = iter_difference_t<Iterator>; // Until C++20, iterator_traits<Iterator>::difference_type;
    394     using pointer           = Iterator;
    395     using reference         = iter_rvalue_reference_t<Iterator>; // Until C++20, value_type&&
    396 
    397     constexpr move_iterator();  // all the constexprs are in C++17
    398     constexpr explicit move_iterator(Iterator i);
    399     template <class U>
    400       constexpr move_iterator(const move_iterator<U>& u);
    401     template <class U>
    402       constexpr move_iterator& operator=(const move_iterator<U>& u);
    403 
    404     constexpr iterator_type base() const; // Until C++20
    405     constexpr const Iterator& base() const & noexcept; // From C++20
    406     constexpr Iterator base() &&; // From C++20
    407 
    408     constexpr reference operator*() const;
    409     constexpr pointer operator->() const; // Deprecated in C++20
    410     constexpr move_iterator& operator++();
    411     constexpr auto operator++(int); // Return type was move_iterator until C++20
    412     constexpr move_iterator& operator--();
    413     constexpr move_iterator operator--(int);
    414     constexpr move_iterator operator+(difference_type n) const;
    415     constexpr move_iterator& operator+=(difference_type n);
    416     constexpr move_iterator operator-(difference_type n) const;
    417     constexpr move_iterator& operator-=(difference_type n);
    418     constexpr reference operator[](difference_type n) const; // Return type unspecified until C++20
    419 
    420     template<sentinel_for<Iterator> S>
    421       friend constexpr bool
    422         operator==(const move_iterator& x, const move_sentinel<S>& y); // Since C++20
    423     template<sized_sentinel_for<Iterator> S>
    424       friend constexpr iter_difference_t<Iterator>
    425         operator-(const move_sentinel<S>& x, const move_iterator& y); // Since C++20
    426     template<sized_sentinel_for<Iterator> S>
    427       friend constexpr iter_difference_t<Iterator>
    428         operator-(const move_iterator& x, const move_sentinel<S>& y); // Since C++20
    429     friend constexpr iter_rvalue_reference_t<Iterator>
    430       iter_move(const move_iterator& i)
    431         noexcept(noexcept(ranges::iter_move(i.current))); // Since C++20
    432     template<indirectly_swappable<Iterator> Iterator2>
    433       friend constexpr void
    434         iter_swap(const move_iterator& x, const move_iterator<Iterator2>& y)
    435           noexcept(noexcept(ranges::iter_swap(x.current, y.current))); // Since C++20
    436 
    437 private:
    438     Iterator current; // exposition only
    439 };
    440 
    441 template <class Iterator1, class Iterator2>
    442 constexpr bool   // constexpr in C++17
    443 operator==(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
    444 
    445 template <class Iterator1, class Iterator2>
    446 constexpr bool   // constexpr in C++17
    447 operator!=(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
    448 
    449 template <class Iterator1, class Iterator2>
    450 constexpr bool   // constexpr in C++17
    451 operator<(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
    452 
    453 template <class Iterator1, class Iterator2>
    454 constexpr bool   // constexpr in C++17
    455 operator<=(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
    456 
    457 template <class Iterator1, class Iterator2>
    458 constexpr bool   // constexpr in C++17
    459 operator>(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
    460 
    461 template <class Iterator1, class Iterator2>
    462 constexpr bool   // constexpr in C++17
    463 operator>=(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);
    464 
    465 template <class Iterator1, class Iterator2>
    466 constexpr auto   // constexpr in C++17
    467 operator-(const move_iterator<Iterator1>& x,
    468           const move_iterator<Iterator2>& y) -> decltype(x.base() - y.base());
    469 
    470 template <class Iterator>
    471 constexpr move_iterator<Iterator> operator+(   // constexpr in C++17
    472             typename move_iterator<Iterator>::difference_type n,
    473             const move_iterator<Iterator>& x);
    474 
    475 template <class Iterator>   // constexpr in C++17
    476 constexpr  move_iterator<Iterator> make_move_iterator(const Iterator& i);
    477 
    478 template<class Iterator1, class Iterator2>
    479     requires (!sized_sentinel_for<Iterator1, Iterator2>)
    480   inline constexpr bool disable_sized_sentinel_for<move_iterator<Iterator1>,    // since C++20
    481                                                     move_iterator<Iterator2>> = true;
    482 
    483 template<semiregular S>
    484 class move_sentinel {
    485 public:
    486   constexpr move_sentinel();
    487   constexpr explicit move_sentinel(S s);
    488   template<class S2>
    489     requires convertible_to<const S2&, S>
    490       constexpr move_sentinel(const move_sentinel<S2>& s);
    491   template<class S2>
    492     requires assignable_from<S&, const S2&>
    493       constexpr move_sentinel& operator=(const move_sentinel<S2>& s);
    494 
    495   constexpr S base() const;
    496 private:
    497   S last;     // exposition only
    498 };
    499 
    500 // [default.sentinel], default sentinel
    501 struct default_sentinel_t;
    502 inline constexpr default_sentinel_t default_sentinel{};
    503 
    504 // [iterators.counted], counted iterators
    505 template<input_or_output_iterator I> class counted_iterator;
    506 
    507 template<input_iterator I>
    508   requires see below
    509   struct iterator_traits<counted_iterator<I>>;
    510 
    511 // [unreachable.sentinel], unreachable sentinel
    512 struct unreachable_sentinel_t;
    513 inline constexpr unreachable_sentinel_t unreachable_sentinel{};
    514 
    515 template <class T, class charT = char, class traits = char_traits<charT>, class Distance = ptrdiff_t>
    516 class istream_iterator
    517     : public iterator<input_iterator_tag, T, Distance, const T*, const T&> // until C++17
    518 {
    519 public:
    520     typedef input_iterator_tag           iterator_category;
    521     typedef T                            value_type;
    522     typedef Distance                     difference_type;
    523     typedef const T*                     pointer;
    524     typedef const T&                     reference;
    525 
    526     typedef charT                        char_type;
    527     typedef traits                       traits_type;
    528     typedef basic_istream<charT, traits> istream_type;
    529 
    530     istream_iterator(); // constexpr since C++11
    531     constexpr istream_iterator(default_sentinel_t); // since C++20
    532     istream_iterator(istream_type& s);
    533     constexpr istream_iterator(const istream_iterator& x) noexcept(see below);
    534     ~istream_iterator();
    535 
    536     const T& operator*() const;
    537     const T* operator->() const;
    538     istream_iterator& operator++();
    539     istream_iterator  operator++(int);
    540     friend bool operator==(const istream_iterator& i, default_sentinel_t); // since C++20
    541 };
    542 
    543 template <class T, class charT, class traits, class Distance>
    544 bool operator==(const istream_iterator<T,charT,traits,Distance>& x,
    545                 const istream_iterator<T,charT,traits,Distance>& y);
    546 template <class T, class charT, class traits, class Distance>
    547 bool operator!=(const istream_iterator<T,charT,traits,Distance>& x,
    548                 const istream_iterator<T,charT,traits,Distance>& y); // until C++20
    549 
    550 template <class T, class charT = char, class traits = char_traits<charT> >
    551 class ostream_iterator
    552     : public iterator<output_iterator_tag, void, void, void, void> // until C++17
    553 {
    554 public:
    555     typedef output_iterator_tag         iterator_category;
    556     typedef void                        value_type;
    557     typedef void                        difference_type; // until C++20
    558     typedef ptrdiff_t                   difference_type; // since C++20
    559     typedef void                        pointer;
    560     typedef void                        reference;
    561 
    562     typedef charT char_type;
    563     typedef traits traits_type;
    564     typedef basic_ostream<charT,traits> ostream_type;
    565 
    566     ostream_iterator(ostream_type& s);
    567     ostream_iterator(ostream_type& s, const charT* delimiter);
    568     ostream_iterator(const ostream_iterator& x);
    569     ~ostream_iterator();
    570     ostream_iterator& operator=(const T& value);
    571 
    572     ostream_iterator& operator*();
    573     ostream_iterator& operator++();
    574     ostream_iterator& operator++(int);
    575 };
    576 
    577 template<class charT, class traits = char_traits<charT> >
    578 class istreambuf_iterator
    579     : public iterator<input_iterator_tag, charT, traits::off_type, unspecified, charT> // until C++17
    580 {
    581 public:
    582     typedef input_iterator_tag              iterator_category;
    583     typedef charT                           value_type;
    584     typedef traits::off_type                difference_type;
    585     typedef unspecified                     pointer;
    586     typedef charT                           reference;
    587 
    588     typedef charT                           char_type;
    589     typedef traits                          traits_type;
    590     typedef traits::int_type                int_type;
    591     typedef basic_streambuf<charT, traits>  streambuf_type;
    592     typedef basic_istream<charT, traits>    istream_type;
    593 
    594     istreambuf_iterator() noexcept; // constexpr since C++11
    595     constexpr istreambuf_iterator(default_sentinel_t) noexcept; // since C++20
    596     istreambuf_iterator(istream_type& s) noexcept;
    597     istreambuf_iterator(streambuf_type* s) noexcept;
    598     istreambuf_iterator(a-private-type) noexcept;
    599 
    600     charT                operator*() const;
    601     pointer operator->() const;
    602     istreambuf_iterator& operator++();
    603     a-private-type       operator++(int);
    604 
    605     bool equal(const istreambuf_iterator& b) const;
    606     friend bool operator==(const istreambuf_iterator& i, default_sentinel_t s); // since C++20
    607 };
    608 
    609 template <class charT, class traits>
    610 bool operator==(const istreambuf_iterator<charT,traits>& a,
    611                 const istreambuf_iterator<charT,traits>& b);
    612 template <class charT, class traits>
    613 bool operator!=(const istreambuf_iterator<charT,traits>& a,
    614                 const istreambuf_iterator<charT,traits>& b); // until C++20
    615 
    616 template <class charT, class traits = char_traits<charT> >
    617 class ostreambuf_iterator
    618     : public iterator<output_iterator_tag, void, void, void, void> // until C++17
    619 {
    620 public:
    621     typedef output_iterator_tag            iterator_category;
    622     typedef void                           value_type;
    623     typedef void                           difference_type; // until C++20
    624     typedef ptrdiff_t                      difference_type; // since C++20
    625     typedef void                           pointer;
    626     typedef void                           reference;
    627 
    628     typedef charT                          char_type;
    629     typedef traits                         traits_type;
    630     typedef basic_streambuf<charT, traits> streambuf_type;
    631     typedef basic_ostream<charT, traits>   ostream_type;
    632 
    633     ostreambuf_iterator(ostream_type& s) noexcept;
    634     ostreambuf_iterator(streambuf_type* s) noexcept;
    635     ostreambuf_iterator& operator=(charT c);
    636     ostreambuf_iterator& operator*();
    637     ostreambuf_iterator& operator++();
    638     ostreambuf_iterator& operator++(int);
    639     bool failed() const noexcept;
    640 };
    641 
    642 template <class C> constexpr auto begin(C& c) -> decltype(c.begin());                   // constexpr since C++17
    643 template <class C> constexpr auto begin(const C& c) -> decltype(c.begin());             // constexpr since C++17
    644 template <class C> constexpr auto end(C& c) -> decltype(c.end());                       // constexpr since C++17
    645 template <class C> constexpr auto end(const C& c) -> decltype(c.end());                 // constexpr since C++17
    646 template <class T, size_t N> constexpr T* begin(T (&array)[N]) noexcept;
    647 template <class T, size_t N> constexpr T* end(T (&array)[N]) noexcept;
    648 
    649 template <class C> constexpr auto cbegin(const C& c) noexcept(see-below) -> decltype(std::begin(c)); // C++14
    650 template <class C> constexpr auto cend(const C& c) noexcept(see-below) -> decltype(std::end(c));     // C++14
    651 template <class C> constexpr auto rbegin(C& c) -> decltype(c.rbegin());                 // C++14, constexpr since C++17
    652 template <class C> constexpr auto rbegin(const C& c) -> decltype(c.rbegin());           // C++14, constexpr since C++17
    653 template <class C> constexpr auto rend(C& c) -> decltype(c.rend());                     // C++14, constexpr since C++17
    654 template <class C> constexpr auto rend(const C& c) -> decltype(c.rend());               // C++14, constexpr since C++17
    655 template <class E> constexpr reverse_iterator<const E*> rbegin(initializer_list<E> il); // C++14, constexpr since C++17
    656 template <class E> constexpr reverse_iterator<const E*> rend(initializer_list<E> il);   // C++14, constexpr since C++17
    657 template <class T, size_t N> constexpr reverse_iterator<T*> rbegin(T (&array)[N]);      // C++14, constexpr since C++17
    658 template <class T, size_t N> constexpr reverse_iterator<T*> rend(T (&array)[N]);        // C++14, constexpr since C++17
    659 template <class C> constexpr auto crbegin(const C& c) -> decltype(std::rbegin(c));      // C++14, constexpr since C++17
    660 template <class C> constexpr auto crend(const C& c) -> decltype(std::rend(c));          // C++14, constexpr since C++17
    661 
    662 // 24.8, container access:
    663 template <class C> constexpr auto size(const C& c) -> decltype(c.size());         // C++17
    664 template <class T, size_t N> constexpr size_t size(const T (&array)[N]) noexcept; // C++17
    665 
    666 template <class C> constexpr auto ssize(const C& c)
    667     -> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;                    // C++20
    668 template <class T, ptrdiff_t> constexpr ptrdiff_t ssize(const T (&array)[N]) noexcept; // C++20
    669 
    670 template <class C> constexpr auto empty(const C& c) -> decltype(c.empty());       // C++17
    671 template <class T, size_t N> constexpr bool empty(const T (&array)[N]) noexcept;  // C++17
    672 template <class E> constexpr bool empty(initializer_list<E> il) noexcept;         // C++17
    673 template <class C> constexpr auto data(C& c) -> decltype(c.data());               // C++17
    674 template <class C> constexpr auto data(const C& c) -> decltype(c.data());         // C++17
    675 template <class T, size_t N> constexpr T* data(T (&array)[N]) noexcept;           // C++17
    676 template <class E> constexpr const E* data(initializer_list<E> il) noexcept;      // C++17
    677 
    678 }  // std
    679 
    680 */
    681 
    682 #if __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
    683 #  include <__cxx03/iterator>
    684 #else
    685 #  include <__config>
    686 #  include <__iterator/access.h>
    687 #  include <__iterator/advance.h>
    688 #  include <__iterator/back_insert_iterator.h>
    689 #  include <__iterator/distance.h>
    690 #  include <__iterator/front_insert_iterator.h>
    691 #  include <__iterator/insert_iterator.h>
    692 #  include <__iterator/istream_iterator.h>
    693 #  include <__iterator/istreambuf_iterator.h>
    694 #  include <__iterator/iterator.h>
    695 #  include <__iterator/iterator_traits.h>
    696 #  include <__iterator/move_iterator.h>
    697 #  include <__iterator/next.h>
    698 #  include <__iterator/ostream_iterator.h>
    699 #  include <__iterator/ostreambuf_iterator.h>
    700 #  include <__iterator/prev.h>
    701 #  include <__iterator/reverse_iterator.h>
    702 #  include <__iterator/wrap_iter.h>
    703 
    704 #  if _LIBCPP_STD_VER >= 14
    705 #    include <__iterator/reverse_access.h>
    706 #  endif
    707 
    708 #  if _LIBCPP_STD_VER >= 17
    709 #    include <__iterator/data.h>
    710 #    include <__iterator/empty.h>
    711 #    include <__iterator/size.h>
    712 #  endif
    713 
    714 #  if _LIBCPP_STD_VER >= 20
    715 #    include <__iterator/common_iterator.h>
    716 #    include <__iterator/concepts.h>
    717 #    include <__iterator/counted_iterator.h>
    718 #    include <__iterator/default_sentinel.h>
    719 #    include <__iterator/incrementable_traits.h>
    720 #    include <__iterator/indirectly_comparable.h>
    721 #    include <__iterator/iter_move.h>
    722 #    include <__iterator/iter_swap.h>
    723 #    include <__iterator/mergeable.h>
    724 #    include <__iterator/move_sentinel.h>
    725 #    include <__iterator/permutable.h>
    726 #    include <__iterator/projected.h>
    727 #    include <__iterator/readable_traits.h>
    728 #    include <__iterator/sortable.h>
    729 #    include <__iterator/unreachable_sentinel.h>
    730 #  endif
    731 
    732 #  include <version>
    733 
    734 // standard-mandated includes
    735 
    736 // [iterator.synopsis]
    737 #  include <compare>
    738 #  include <concepts>
    739 
    740 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
    741 #    pragma GCC system_header
    742 #  endif
    743 
    744 #  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 17
    745 #    include <variant>
    746 #  endif
    747 
    748 #  if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
    749 #    include <cstddef>
    750 #    include <cstdlib>
    751 #    include <exception>
    752 #    include <new>
    753 #    include <type_traits>
    754 #    include <typeinfo>
    755 #    include <utility>
    756 #  endif
    757 #endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
    758 
    759 #endif // _LIBCPP_ITERATOR