xref: /llvm-project-15.0.7/libcxx/include/iterator (revision 79a2b4ba)

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_ITERATOR
#define _LIBCPP_ITERATOR

/*
    iterator synopsis

#include <concepts>

namespace std
{
template<class> struct incrementable_traits;       // since C++20
template<class T>
  using iter_difference_t = see below;             // since C++20

template<class> struct indirectly_readable_traits; // since C++20
template<class T>
  using iter_value_t = see below;                  // since C++20

template<class Iterator>
struct iterator_traits;

template<class T>
  requires is_object_v<T>                    // since C++20
struct iterator_traits<T*>;

template<dereferenceable T>
  using iter_reference_t = decltype(*declval<T&>());

namespace ranges::inline unspecified {
    inline constexpr unspecified iter_move = unspecified; // since C++20, nodiscard as an extension
}}

template<dereferenceable T>
  requires ...
using iter_rvalue_reference_t = decltype(ranges::iter_move(declval<T&>())); // since C++20

// [iterator.concepts], iterator concepts
// [iterator.concept.readable], concept indirectly_readable
template<class In>
  concept indirectly_readable = see below;                      // since C++20

template<indirectly_readable T>
  using iter_common_reference_t =
    common_reference_t<iter_reference_t<T>, iter_value_t<T>&>;  // since C++20

// [iterator.concept.writable], concept indirectly_writable
template<class Out, class T>
  concept indirectly_writable = see below;                // since C++20

// [iterator.concept.winc], concept weakly_incrementable
template<class I>
  concept weakly_incrementable = see below;                // since C++20

// [iterator.concept.inc], concept incrementable
template<class I>
  concept incrementable = see below;                       // since C++20

// [iterator.concept.iterator], concept input_or_output_iterator
  template<class I>
    concept input_or_output_iterator = see below;          // since C++20

// [iterator.concept.sentinel], concept sentinel_for
template<class S, class I>
  concept sentinel_for = see below;                        // since C++20

// [iterator.concept.sizedsentinel], concept sized_sentinel_for
template<class S, class I>
  inline constexpr bool disable_sized_sentinel_for = false;

template<class S, class I>
  concept sized_sentinel_for = see below;

// [iterator.concept.input], concept input_iterator
template<class I>
  concept input_iterator = see below;                      // since C++20

// [iterator.concept.output], concept output_iterator
template<class I, class T>
  concept output_iterator = see below;                     // since C++20

// [iterator.concept.forward], concept forward_iterator
template<class I>
  concept forward_iterator = see below;                    // since C++20

// [iterator.concept.bidir], concept bidirectional_iterator
template<class I>
  concept bidirectional_iterator = see below;              // since C++20

// [iterator.concept.random.access], concept random_access_iterator
template<class I>
  concept random_access_iterator = see below;              // since C++20

// [indirectcallable]
// [indirectcallable.indirectinvocable]
template<class F, class I>
  concept indirectly_unary_invocable = see below;          // since C++20

template<class F, class I>
  concept indirectly_regular_unary_invocable = see below;  // since C++20

template<class F, class I>
  concept indirect_unary_predicate = see below;            // since C++20

template<class F, class I1, class I2>
  concept indirect_binary_predicate = see below;           // since C++20

template<class F, class I1, class I2 = I1>
  concept indirect_equivalence_relation = see below;       // since C++20

template<class F, class I1, class I2 = I1>
  concept indirect_strict_weak_order = see below;          // since C++20

template<class F, class... Is>
  using indirect_result_t = see below;                     // since C++20

// [projected], projected
template<indirectly_readable I, indirectly_regular_unary_invocable<I> Proj>
  struct projected;                                        // since C++20

template<weakly_incrementable I, indirectly_regular_unary_invocable<I> Proj>
  struct incrementable_traits<projected<I, Proj>>;         // since C++20

// [alg.req.ind.move], concept indirectly_movable
template<class In, class Out>
  concept indirectly_movable = see below;                  // since C++20

template<class In, class Out>
  concept indirectly_movable_storable = see below;         // since C++20

// [alg.req.ind.copy], concept indirectly_copyable
template<class In, class Out>
  concept indirectly_copyable = see below;                 // since C++20

template<class In, class Out>
  concept indirectly_copyable_storable = see below;        // since C++20

// [alg.req.ind.swap], concept indirectly_swappable
template<class I1, class I2 = I1>
  concept indirectly_swappable = see below;                // since C++20

template<class I1, class I2, class R, class P1 = identity,
         class P2 = identity>
  concept indirectly_comparable =
    indirect_binary_predicate<R, projected<I1, P1>, projected<I2, P2>>; // since C++20

// [alg.req.permutable], concept permutable
template<class I>
  concept permutable = see below;                          // since C++20

 // [alg.req.mergeable], concept mergeable
template<class I1, class I2, class Out,
    class R = ranges::less, class P1 = identity, class P2 = identity>
  concept mergeable = see below;                           // since C++20

// [alg.req.sortable], concept sortable
template<class I, class R = ranges::less, class P = identity>
  concept sortable = see below;                            // since C++20

template<input_or_output_iterator I, sentinel_for<I> S>
  requires (!same_as<I, S> && copyable<I>)
class common_iterator;                                     // since C++20

template<class Category, class T, class Distance = ptrdiff_t,
         class Pointer = T*, class Reference = T&>
struct iterator                                            // deprecated in C++17
{
    typedef T         value_type;
    typedef Distance  difference_type;
    typedef Pointer   pointer;
    typedef Reference reference;
    typedef Category  iterator_category;
};

struct input_iterator_tag  {};
struct output_iterator_tag {};
struct forward_iterator_tag       : public input_iterator_tag         {};
struct bidirectional_iterator_tag : public forward_iterator_tag       {};
struct random_access_iterator_tag : public bidirectional_iterator_tag {};
struct contiguous_iterator_tag    : public random_access_iterator_tag {};

// 27.4.3, iterator operations
template <class InputIterator, class Distance>  // constexpr in C++17
  constexpr void advance(InputIterator& i, Distance n);

template <class InputIterator>  // constexpr in C++17
  constexpr typename iterator_traits<InputIterator>::difference_type
    distance(InputIterator first, InputIterator last);

template <class InputIterator>  // constexpr in C++17
  constexpr InputIterator next(InputIterator x,
typename iterator_traits<InputIterator>::difference_type n = 1);

template <class BidirectionalIterator>  // constexpr in C++17
  constexpr BidirectionalIterator prev(BidirectionalIterator x,
    typename iterator_traits<BidirectionalIterator>::difference_type n = 1);

// [range.iter.ops], range iterator operations
namespace ranges {
  // [range.iter.op.advance], ranges::advance
  template<input_or_output_iterator I>
    constexpr void advance(I& i, iter_difference_t<I> n);                          // since C++20
  template<input_or_output_iterator I, sentinel_for<I> S>
    constexpr void advance(I& i, S bound);                                         // since C++20
  template<input_or_output_iterator I, sentinel_for<I> S>
    constexpr iter_difference_t<I> advance(I& i, iter_difference_t<I> n, S bound); // since C++20
}

template <class Iterator>
class reverse_iterator
    : public iterator<typename iterator_traits<Iterator>::iterator_category, // until C++17
                      typename iterator_traits<Iterator>::value_type,
                      typename iterator_traits<Iterator>::difference_type,
                      typename iterator_traits<Iterator>::pointer,
                      typename iterator_traits<Iterator>::reference>
{
protected:
    Iterator current;
public:
    using iterator_type     = Iterator;
    using iterator_concept  = see below; // since C++20
    using iterator_category = typename iterator_traits<Iterator>::iterator_category; // since C++17, until C++20
    using iterator_category = see below; // since C++20
    using value_type        = typename iterator_traits<Iterator>::value_type; // since C++17, until C++20
    using value_type        = iter_value_t<Iterator>; // since C++20
    using difference_type   = typename iterator_traits<Iterator>::difference_type; // until C++20
    using difference_type   = iter_difference_t<Iterator>; // since C++20
    using pointer           = typename iterator_traits<Iterator>::pointer;
    using reference         = typename iterator_traits<Iterator>::reference; // until C++20
    using reference         = iter_reference_t<Iterator>; // since C++20

    constexpr reverse_iterator();
    constexpr explicit reverse_iterator(Iterator x);
    template <class U> constexpr reverse_iterator(const reverse_iterator<U>& u);
    template <class U> constexpr reverse_iterator& operator=(const reverse_iterator<U>& u);
    constexpr Iterator base() const;
    constexpr reference operator*() const;
    constexpr pointer   operator->() const; // until C++20
    constexpr pointer   operator->() const requires see below; // since C++20
    constexpr reverse_iterator& operator++();
    constexpr reverse_iterator  operator++(int);
    constexpr reverse_iterator& operator--();
    constexpr reverse_iterator  operator--(int);
    constexpr reverse_iterator  operator+ (difference_type n) const;
    constexpr reverse_iterator& operator+=(difference_type n);
    constexpr reverse_iterator  operator- (difference_type n) const;
    constexpr reverse_iterator& operator-=(difference_type n);
    constexpr unspecified       operator[](difference_type n) const;

    friend constexpr iter_rvalue_reference_t<Iterator>
      iter_move(const reverse_iterator& i) noexcept(see below);
    template<indirectly_swappable<Iterator> Iterator2>
      friend constexpr void
        iter_swap(const reverse_iterator& x,
                  const reverse_iterator<Iterator2>& y) noexcept(see below);
};

template <class Iterator1, class Iterator2>
constexpr bool                          // constexpr in C++17
operator==(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool                          // constexpr in C++17
operator!=(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool                          // constexpr in C++17
operator<(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool                          // constexpr in C++17
operator>(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool                          // constexpr in C++17
operator<=(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool                          // constexpr in C++17
operator>=(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y);

template<class Iterator1, three_way_comparable_with<Iterator1> Iterator2>
  constexpr compare_three_way_result_t<Iterator1, Iterator2>
    operator<=>(const reverse_iterator<Iterator1>& x,
                const reverse_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr auto
operator-(const reverse_iterator<Iterator1>& x, const reverse_iterator<Iterator2>& y)
-> decltype(__y.base() - __x.base());   // constexpr in C++17

template <class Iterator>
constexpr reverse_iterator<Iterator>
operator+(typename reverse_iterator<Iterator>::difference_type n,
          const reverse_iterator<Iterator>& x);   // constexpr in C++17

template <class Iterator>
constexpr reverse_iterator<Iterator> make_reverse_iterator(Iterator i); // C++14, constexpr in C++17

template<class Iterator1, class Iterator2>
    requires (!sized_sentinel_for<Iterator1, Iterator2>)
  inline constexpr bool disable_sized_sentinel_for<reverse_iterator<Iterator1>,
                                                   reverse_iterator<Iterator2>> = true;

template <class Container>
class back_insert_iterator
    : public iterator<output_iterator_tag, void, void, void, void> // until C++17
{
protected:
    Container* container;
public:
    typedef Container                   container_type;
    typedef void                        value_type;
    typedef void                        difference_type; // until C++20
    typedef ptrdiff_t                   difference_type; // since C++20
    typedef void                        reference;
    typedef void                        pointer;

    explicit back_insert_iterator(Container& x);  // constexpr in C++20
    back_insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
    back_insert_iterator& operator*();  // constexpr in C++20
    back_insert_iterator& operator++();  // constexpr in C++20
    back_insert_iterator  operator++(int);  // constexpr in C++20
};

template <class Container> back_insert_iterator<Container> back_inserter(Container& x);  // constexpr in C++20

template <class Container>
class front_insert_iterator
    : public iterator<output_iterator_tag, void, void, void, void> // until C++17
{
protected:
    Container* container;
public:
    typedef Container                    container_type;
    typedef void                         value_type;
    typedef void                         difference_type; // until C++20
    typedef ptrdiff_t                    difference_type; // since C++20
    typedef void                         reference;
    typedef void                         pointer;

    explicit front_insert_iterator(Container& x);  // constexpr in C++20
    front_insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
    front_insert_iterator& operator*();  // constexpr in C++20
    front_insert_iterator& operator++();  // constexpr in C++20
    front_insert_iterator  operator++(int);  // constexpr in C++20
};

template <class Container> front_insert_iterator<Container> front_inserter(Container& x);  // constexpr in C++20

template <class Container>
class insert_iterator
    : public iterator<output_iterator_tag, void, void, void, void> // until C++17
{
protected:
    Container* container;
    typename Container::iterator iter;
public:
    typedef Container              container_type;
    typedef void                   value_type;
    typedef void                   difference_type; // until C++20
    typedef ptrdiff_t              difference_type; // since C++20
    typedef void                   reference;
    typedef void                   pointer;

    insert_iterator(Container& x, typename Container::iterator i);  // constexpr in C++20
    insert_iterator& operator=(const typename Container::value_type& value);  // constexpr in C++20
    insert_iterator& operator*();  // constexpr in C++20
    insert_iterator& operator++();  // constexpr in C++20
    insert_iterator& operator++(int);  // constexpr in C++20
};

template <class Container>
insert_iterator<Container> inserter(Container& x, typename Container::iterator i);  // until C++20
template <class Container>
constexpr insert_iterator<Container> inserter(Container& x, ranges::iterator_t<Container> i);  // since C++20

template <class Iterator>
class move_iterator {
public:
    using iterator_type     = Iterator;
    using iterator_concept  = input_iterator_tag; // From C++20
    using iterator_category = see below; // not always present starting from C++20
    using value_type        = iter_value_t<Iterator>; // Until C++20, iterator_traits<Iterator>::value_type
    using difference_type   = iter_difference_t<Iterator>; // Until C++20, iterator_traits<Iterator>::difference_type;
    using pointer           = Iterator;
    using reference         = iter_rvalue_reference_t<Iterator>; // Until C++20, value_type&&

    constexpr move_iterator();  // all the constexprs are in C++17
    constexpr explicit move_iterator(Iterator i);
    template <class U>
      constexpr move_iterator(const move_iterator<U>& u);
    template <class U>
      constexpr move_iterator& operator=(const move_iterator<U>& u);

    constexpr iterator_type base() const; // Until C++20
    constexpr const Iterator& base() const & noexcept; // From C++20
    constexpr Iterator base() &&; // From C++20

    constexpr reference operator*() const;
    constexpr pointer operator->() const; // Deprecated in C++20
    constexpr move_iterator& operator++();
    constexpr auto operator++(int); // Return type was move_iterator until C++20
    constexpr move_iterator& operator--();
    constexpr move_iterator operator--(int);
    constexpr move_iterator operator+(difference_type n) const;
    constexpr move_iterator& operator+=(difference_type n);
    constexpr move_iterator operator-(difference_type n) const;
    constexpr move_iterator& operator-=(difference_type n);
    constexpr reference operator[](difference_type n) const; // Return type unspecified until C++20

    template<sentinel_for<Iterator> S>
      friend constexpr bool
        operator==(const move_iterator& x, const move_sentinel<S>& y); // Since C++20
    template<sized_sentinel_for<Iterator> S>
      friend constexpr iter_difference_t<Iterator>
        operator-(const move_sentinel<S>& x, const move_iterator& y); // Since C++20
    template<sized_sentinel_for<Iterator> S>
      friend constexpr iter_difference_t<Iterator>
        operator-(const move_iterator& x, const move_sentinel<S>& y); // Since C++20
    friend constexpr iter_rvalue_reference_t<Iterator>
      iter_move(const move_iterator& i)
        noexcept(noexcept(ranges::iter_move(i.current))); // Since C++20
    template<indirectly_swappable<Iterator> Iterator2>
      friend constexpr void
        iter_swap(const move_iterator& x, const move_iterator<Iterator2>& y)
          noexcept(noexcept(ranges::iter_swap(x.current, y.current))); // Since C++20

private:
    Iterator current; // exposition only
};

template <class Iterator1, class Iterator2>
constexpr bool   // constexpr in C++17
operator==(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool   // constexpr in C++17
operator!=(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool   // constexpr in C++17
operator<(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool   // constexpr in C++17
operator<=(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool   // constexpr in C++17
operator>(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr bool   // constexpr in C++17
operator>=(const move_iterator<Iterator1>& x, const move_iterator<Iterator2>& y);

template <class Iterator1, class Iterator2>
constexpr auto   // constexpr in C++17
operator-(const move_iterator<Iterator1>& x,
          const move_iterator<Iterator2>& y) -> decltype(x.base() - y.base());

template <class Iterator>
constexpr move_iterator<Iterator> operator+(   // constexpr in C++17
            typename move_iterator<Iterator>::difference_type n,
            const move_iterator<Iterator>& x);

template <class Iterator>   // constexpr in C++17
constexpr  move_iterator<Iterator> make_move_iterator(const Iterator& i);

template<semiregular S>
class move_sentinel {
public:
  constexpr move_sentinel();
  constexpr explicit move_sentinel(S s);
  template<class S2>
    requires convertible_to<const S2&, S>
      constexpr move_sentinel(const move_sentinel<S2>& s);
  template<class S2>
    requires assignable_from<S&, const S2&>
      constexpr move_sentinel& operator=(const move_sentinel<S2>& s);

  constexpr S base() const;
private:
  S last;     // exposition only
};

// [default.sentinel], default sentinel
struct default_sentinel_t;
inline constexpr default_sentinel_t default_sentinel{};

// [iterators.counted], counted iterators
template<input_or_output_iterator I> class counted_iterator;

template<input_iterator I>
  requires see below
  struct iterator_traits<counted_iterator<I>>;

// [unreachable.sentinel], unreachable sentinel
struct unreachable_sentinel_t;
inline constexpr unreachable_sentinel_t unreachable_sentinel{};

template <class T, class charT = char, class traits = char_traits<charT>, class Distance = ptrdiff_t>
class istream_iterator
    : public iterator<input_iterator_tag, T, Distance, const T*, const T&> // until C++17
{
public:
    typedef input_iterator_tag           iterator_category;
    typedef T                            value_type;
    typedef Distance                     difference_type;
    typedef const T*                     pointer;
    typedef const T&                     reference;

    typedef charT                        char_type;
    typedef traits                       traits_type;
    typedef basic_istream<charT, traits> istream_type;

    istream_iterator(); // constexpr since C++11
    constexpr istream_iterator(default_sentinel_t); // since C++20
    istream_iterator(istream_type& s);
    istream_iterator(const istream_iterator& x);
    ~istream_iterator();

    const T& operator*() const;
    const T* operator->() const;
    istream_iterator& operator++();
    istream_iterator  operator++(int);
    friend bool operator==(const istream_iterator& i, default_sentinel_t); // since C++20
};

template <class T, class charT, class traits, class Distance>
bool operator==(const istream_iterator<T,charT,traits,Distance>& x,
                const istream_iterator<T,charT,traits,Distance>& y);
template <class T, class charT, class traits, class Distance>
bool operator!=(const istream_iterator<T,charT,traits,Distance>& x,
                const istream_iterator<T,charT,traits,Distance>& y); // until C++20

template <class T, class charT = char, class traits = char_traits<charT> >
class ostream_iterator
    : public iterator<output_iterator_tag, void, void, void, void> // until C++17
{
public:
    typedef output_iterator_tag         iterator_category;
    typedef void                        value_type;
    typedef void                        difference_type; // until C++20
    typedef ptrdiff_t                   difference_type; // since C++20
    typedef void                        pointer;
    typedef void                        reference;

    typedef charT char_type;
    typedef traits traits_type;
    typedef basic_ostream<charT,traits> ostream_type;

    ostream_iterator(ostream_type& s);
    ostream_iterator(ostream_type& s, const charT* delimiter);
    ostream_iterator(const ostream_iterator& x);
    ~ostream_iterator();
    ostream_iterator& operator=(const T& value);

    ostream_iterator& operator*();
    ostream_iterator& operator++();
    ostream_iterator& operator++(int);
};

template<class charT, class traits = char_traits<charT> >
class istreambuf_iterator
    : public iterator<input_iterator_tag, charT, traits::off_type, unspecified, charT> // until C++17
{
public:
    typedef input_iterator_tag              iterator_category;
    typedef charT                           value_type;
    typedef traits::off_type                difference_type;
    typedef unspecified                     pointer;
    typedef charT                           reference;

    typedef charT                           char_type;
    typedef traits                          traits_type;
    typedef traits::int_type                int_type;
    typedef basic_streambuf<charT, traits>  streambuf_type;
    typedef basic_istream<charT, traits>    istream_type;

    istreambuf_iterator() noexcept; // constexpr since C++11
    constexpr istreambuf_iterator(default_sentinel_t) noexcept; // since C++20
    istreambuf_iterator(istream_type& s) noexcept;
    istreambuf_iterator(streambuf_type* s) noexcept;
    istreambuf_iterator(a-private-type) noexcept;

    charT                operator*() const;
    pointer operator->() const;
    istreambuf_iterator& operator++();
    a-private-type       operator++(int);

    bool equal(const istreambuf_iterator& b) const;
    friend bool operator==(const istreambuf_iterator& i, default_sentinel_t s); // since C++20
};

template <class charT, class traits>
bool operator==(const istreambuf_iterator<charT,traits>& a,
                const istreambuf_iterator<charT,traits>& b);
template <class charT, class traits>
bool operator!=(const istreambuf_iterator<charT,traits>& a,
                const istreambuf_iterator<charT,traits>& b); // until C++20

template <class charT, class traits = char_traits<charT> >
class ostreambuf_iterator
    : public iterator<output_iterator_tag, void, void, void, void> // until C++17
{
public:
    typedef output_iterator_tag            iterator_category;
    typedef void                           value_type;
    typedef void                           difference_type; // until C++20
    typedef ptrdiff_t                      difference_type; // since C++20
    typedef void                           pointer;
    typedef void                           reference;

    typedef charT                          char_type;
    typedef traits                         traits_type;
    typedef basic_streambuf<charT, traits> streambuf_type;
    typedef basic_ostream<charT, traits>   ostream_type;

    ostreambuf_iterator(ostream_type& s) noexcept;
    ostreambuf_iterator(streambuf_type* s) noexcept;
    ostreambuf_iterator& operator=(charT c);
    ostreambuf_iterator& operator*();
    ostreambuf_iterator& operator++();
    ostreambuf_iterator& operator++(int);
    bool failed() const noexcept;
};

template <class C> constexpr auto begin(C& c) -> decltype(c.begin());
template <class C> constexpr auto begin(const C& c) -> decltype(c.begin());
template <class C> constexpr auto end(C& c) -> decltype(c.end());
template <class C> constexpr auto end(const C& c) -> decltype(c.end());
template <class T, size_t N> constexpr T* begin(T (&array)[N]);
template <class T, size_t N> constexpr T* end(T (&array)[N]);

template <class C> auto constexpr cbegin(const C& c) -> decltype(std::begin(c));        // C++14
template <class C> auto constexpr cend(const C& c) -> decltype(std::end(c));            // C++14
template <class C> auto constexpr rbegin(C& c) -> decltype(c.rbegin());                 // C++14
template <class C> auto constexpr rbegin(const C& c) -> decltype(c.rbegin());           // C++14
template <class C> auto constexpr rend(C& c) -> decltype(c.rend());                     // C++14
template <class C> constexpr auto rend(const C& c) -> decltype(c.rend());               // C++14
template <class E> reverse_iterator<const E*> constexpr rbegin(initializer_list<E> il); // C++14
template <class E> reverse_iterator<const E*> constexpr rend(initializer_list<E> il);   // C++14
template <class T, size_t N> reverse_iterator<T*> constexpr rbegin(T (&array)[N]);      // C++14
template <class T, size_t N> reverse_iterator<T*> constexpr rend(T (&array)[N]);        // C++14
template <class C> constexpr auto crbegin(const C& c) -> decltype(std::rbegin(c));      // C++14
template <class C> constexpr auto crend(const C& c) -> decltype(std::rend(c));          // C++14

// 24.8, container access:
template <class C> constexpr auto size(const C& c) -> decltype(c.size());         // C++17
template <class T, size_t N> constexpr size_t size(const T (&array)[N]) noexcept; // C++17

template <class C> constexpr auto ssize(const C& c)
    -> common_type_t<ptrdiff_t, make_signed_t<decltype(c.size())>>;                    // C++20
template <class T, ptrdiff_t> constexpr ptrdiff_t ssize(const T (&array)[N]) noexcept; // C++20

template <class C> constexpr auto empty(const C& c) -> decltype(c.empty());       // C++17
template <class T, size_t N> constexpr bool empty(const T (&array)[N]) noexcept;  // C++17
template <class E> constexpr bool empty(initializer_list<E> il) noexcept;         // C++17
template <class C> constexpr auto data(C& c) -> decltype(c.data());               // C++17
template <class C> constexpr auto data(const C& c) -> decltype(c.data());         // C++17
template <class T, size_t N> constexpr T* data(T (&array)[N]) noexcept;           // C++17
template <class E> constexpr const E* data(initializer_list<E> il) noexcept;      // C++17

}  // std

*/

#include <__assert> // all public C++ headers provide the assertion handler
#include <__config>
#include <__debug>
#include <__iterator/access.h>
#include <__iterator/advance.h>
#include <__iterator/back_insert_iterator.h>
#include <__iterator/bounded_iter.h>
#include <__iterator/common_iterator.h>
#include <__iterator/concepts.h>
#include <__iterator/counted_iterator.h>
#include <__iterator/data.h>
#include <__iterator/default_sentinel.h>
#include <__iterator/distance.h>
#include <__iterator/empty.h>
#include <__iterator/erase_if_container.h>
#include <__iterator/front_insert_iterator.h>
#include <__iterator/incrementable_traits.h>
#include <__iterator/indirectly_comparable.h>
#include <__iterator/insert_iterator.h>
#include <__iterator/istream_iterator.h>
#include <__iterator/istreambuf_iterator.h>
#include <__iterator/iter_move.h>
#include <__iterator/iter_swap.h>
#include <__iterator/iterator.h>
#include <__iterator/iterator_traits.h>
#include <__iterator/mergeable.h>
#include <__iterator/move_iterator.h>
#include <__iterator/move_sentinel.h>
#include <__iterator/next.h>
#include <__iterator/ostream_iterator.h>
#include <__iterator/ostreambuf_iterator.h>
#include <__iterator/permutable.h>
#include <__iterator/prev.h>
#include <__iterator/projected.h>
#include <__iterator/readable_traits.h>
#include <__iterator/reverse_access.h>
#include <__iterator/reverse_iterator.h>
#include <__iterator/size.h>
#include <__iterator/sortable.h>
#include <__iterator/unreachable_sentinel.h>
#include <__iterator/wrap_iter.h>
#include <__memory/addressof.h>
#include <__memory/pointer_traits.h>
#include <compare>
#include <concepts> // Mandated by the Standard.
#include <cstddef>
#include <initializer_list>
#include <type_traits>
#include <version>

#ifndef _LIBCPP_REMOVE_TRANSITIVE_INCLUDES
#  include <exception>
#  include <new>
#  include <typeinfo>
#  include <utility>
#endif

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#  pragma GCC system_header
#endif

#endif // _LIBCPP_ITERATOR