libcxx/include/__iterator/reverse_iterator.h

// -*- 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_REVERSE_ITERATOR_H
#define _LIBCPP___ITERATOR_REVERSE_ITERATOR_H

#include <__algorithm/unwrap_iter.h>
#include <__compare/compare_three_way_result.h>
#include <__compare/three_way_comparable.h>
#include <__concepts/convertible_to.h>
#include <__config>
#include <__iterator/concepts.h>
#include <__iterator/incrementable_traits.h>
#include <__iterator/iter_move.h>
#include <__iterator/iter_swap.h>
#include <__iterator/iterator.h>
#include <__iterator/iterator_traits.h>
#include <__memory/addressof.h>
#include <__type_traits/conditional.h>
#include <__type_traits/enable_if.h>
#include <__type_traits/is_assignable.h>
#include <__type_traits/is_convertible.h>
#include <__type_traits/is_nothrow_constructible.h>
#include <__type_traits/is_pointer.h>
#include <__type_traits/is_same.h>
#include <__utility/declval.h>

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

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Iter>
class reverse_iterator
    : public __iterator_base<reverse_iterator<_Iter>,
                             typename iterator_traits<_Iter>::iterator_category,
                             typename iterator_traits<_Iter>::value_type,
                             typename iterator_traits<_Iter>::difference_type,
                             typename iterator_traits<_Iter>::pointer,
                             typename iterator_traits<_Iter>::reference> {
private:
#ifndef _LIBCPP_ABI_NO_REVERSE_ITERATOR_SECOND_MEMBER
  _Iter __t_; // no longer used as of LWG #2360, not removed due to ABI break
#endif

#if _LIBCPP_STD_VER >= 20
  static_assert(__has_bidirectional_iterator_category<_Iter>::value || bidirectional_iterator<_Iter>,
                "reverse_iterator<It> requires It to be a bidirectional iterator.");
#endif // _LIBCPP_STD_VER >= 20

protected:
  _Iter current;

public:
  using iterator_type = _Iter;

  using iterator_category =
      _If<__has_random_access_iterator_category<_Iter>::value,
          random_access_iterator_tag,
          typename iterator_traits<_Iter>::iterator_category>;
  using pointer = typename iterator_traits<_Iter>::pointer;
#if _LIBCPP_STD_VER >= 20
  using iterator_concept = _If<random_access_iterator<_Iter>, random_access_iterator_tag, bidirectional_iterator_tag>;
  using value_type       = iter_value_t<_Iter>;
  using difference_type  = iter_difference_t<_Iter>;
  using reference        = iter_reference_t<_Iter>;
#else
  using value_type      = typename iterator_traits<_Iter>::value_type;
  using difference_type = typename iterator_traits<_Iter>::difference_type;
  using reference       = typename iterator_traits<_Iter>::reference;
#endif

#ifndef _LIBCPP_ABI_NO_REVERSE_ITERATOR_SECOND_MEMBER
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator() : __t_(), current() {}

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 explicit reverse_iterator(_Iter __x) : __t_(__x), current(__x) {}

  template <class _Up, __enable_if_t<!is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator(const reverse_iterator<_Up>& __u)
      : __t_(__u.base()), current(__u.base()) {}

  template <class _Up,
            __enable_if_t<!is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value &&
                              is_assignable<_Iter&, _Up const&>::value,
                          int> = 0>
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator=(const reverse_iterator<_Up>& __u) {
    __t_ = current = __u.base();
    return *this;
  }
#else
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator() : current() {}

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 explicit reverse_iterator(_Iter __x) : current(__x) {}

  template <class _Up, __enable_if_t<!is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value, int> = 0>
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator(const reverse_iterator<_Up>& __u)
      : current(__u.base()) {}

  template <class _Up,
            __enable_if_t<!is_same<_Up, _Iter>::value && is_convertible<_Up const&, _Iter>::value &&
                              is_assignable<_Iter&, _Up const&>::value,
                          int> = 0>
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator=(const reverse_iterator<_Up>& __u) {
    current = __u.base();
    return *this;
  }
#endif
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 _Iter base() const { return current; }
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reference operator*() const {
    _Iter __tmp = current;
    return *--__tmp;
  }

#if _LIBCPP_STD_VER >= 20
  _LIBCPP_HIDE_FROM_ABI constexpr pointer operator->() const
    requires is_pointer_v<_Iter> || requires(const _Iter __i) { __i.operator->(); }
  {
    _Iter __tmp = current;
    --__tmp;
    if constexpr (is_pointer_v<_Iter>) {
      return __tmp;
    } else {
      return __tmp.operator->();
    }
  }
#else
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pointer operator->() const { return std::addressof(operator*()); }
#endif // _LIBCPP_STD_VER >= 20

  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator++() {
    --current;
    return *this;
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator operator++(int) {
    reverse_iterator __tmp(*this);
    --current;
    return __tmp;
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator--() {
    ++current;
    return *this;
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator operator--(int) {
    reverse_iterator __tmp(*this);
    ++current;
    return __tmp;
  }
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator
  operator+(difference_type __n) const {
    return reverse_iterator(current - __n);
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator+=(difference_type __n) {
    current -= __n;
    return *this;
  }
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator
  operator-(difference_type __n) const {
    return reverse_iterator(current + __n);
  }
  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator& operator-=(difference_type __n) {
    current += __n;
    return *this;
  }
  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reference
  operator[](difference_type __n) const {
    return *(*this + __n);
  }

#if _LIBCPP_STD_VER >= 20
  [[nodiscard]]
  _LIBCPP_HIDE_FROM_ABI friend constexpr iter_rvalue_reference_t<_Iter> iter_move(const reverse_iterator& __i) noexcept(
      is_nothrow_copy_constructible_v<_Iter> && noexcept(ranges::iter_move(--std::declval<_Iter&>()))) {
    auto __tmp = __i.base();
    return ranges::iter_move(--__tmp);
  }

  template <indirectly_swappable<_Iter> _Iter2>
  _LIBCPP_HIDE_FROM_ABI friend constexpr void
  iter_swap(const reverse_iterator& __x, const reverse_iterator<_Iter2>& __y) noexcept(
      is_nothrow_copy_constructible_v<_Iter> && is_nothrow_copy_constructible_v<_Iter2> &&
      noexcept(ranges::iter_swap(--std::declval<_Iter&>(), --std::declval<_Iter2&>()))) {
    auto __xtmp = __x.base();
    auto __ytmp = __y.base();
    ranges::iter_swap(--__xtmp, --__ytmp);
  }
#endif // _LIBCPP_STD_VER >= 20
};

template <class _Iter1, class _Iter2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
operator==(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
#if _LIBCPP_STD_VER >= 20
  requires requires {
    { __x.base() == __y.base() } -> convertible_to<bool>;
  }
#endif // _LIBCPP_STD_VER >= 20
{
  return __x.base() == __y.base();
}

template <class _Iter1, class _Iter2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
operator<(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
#if _LIBCPP_STD_VER >= 20
  requires requires {
    { __x.base() > __y.base() } -> convertible_to<bool>;
  }
#endif // _LIBCPP_STD_VER >= 20
{
  return __x.base() > __y.base();
}

template <class _Iter1, class _Iter2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
operator!=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
#if _LIBCPP_STD_VER >= 20
  requires requires {
    { __x.base() != __y.base() } -> convertible_to<bool>;
  }
#endif // _LIBCPP_STD_VER >= 20
{
  return __x.base() != __y.base();
}

template <class _Iter1, class _Iter2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
operator>(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
#if _LIBCPP_STD_VER >= 20
  requires requires {
    { __x.base() < __y.base() } -> convertible_to<bool>;
  }
#endif // _LIBCPP_STD_VER >= 20
{
  return __x.base() < __y.base();
}

template <class _Iter1, class _Iter2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
operator>=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
#if _LIBCPP_STD_VER >= 20
  requires requires {
    { __x.base() <= __y.base() } -> convertible_to<bool>;
  }
#endif // _LIBCPP_STD_VER >= 20
{
  return __x.base() <= __y.base();
}

template <class _Iter1, class _Iter2>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 bool
operator<=(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
#if _LIBCPP_STD_VER >= 20
  requires requires {
    { __x.base() >= __y.base() } -> convertible_to<bool>;
  }
#endif // _LIBCPP_STD_VER >= 20
{
  return __x.base() >= __y.base();
}

#if _LIBCPP_STD_VER >= 20
template <class _Iter1, three_way_comparable_with<_Iter1> _Iter2>
_LIBCPP_HIDE_FROM_ABI constexpr compare_three_way_result_t<_Iter1, _Iter2>
operator<=>(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) {
  return __y.base() <=> __x.base();
}
#endif // _LIBCPP_STD_VER >= 20

#ifndef _LIBCPP_CXX03_LANG
template <class _Iter1, class _Iter2>
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
_LIBCPP_CONSTEXPR_SINCE_CXX17 auto operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
    -> decltype(__y.base() - __x.base()) {
  return __y.base() - __x.base();
}
#else
template <class _Iter1, class _Iter2>
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI typename reverse_iterator<_Iter1>::difference_type
operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y) {
  return __y.base() - __x.base();
}
#endif

template <class _Iter>
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator<_Iter>
operator+(typename reverse_iterator<_Iter>::difference_type __n, const reverse_iterator<_Iter>& __x) {
  return reverse_iterator<_Iter>(__x.base() - __n);
}

#if _LIBCPP_STD_VER >= 20
template <class _Iter1, class _Iter2>
  requires(!sized_sentinel_for<_Iter1, _Iter2>)
inline constexpr bool disable_sized_sentinel_for<reverse_iterator<_Iter1>, reverse_iterator<_Iter2>> = true;
#endif // _LIBCPP_STD_VER >= 20

#if _LIBCPP_STD_VER >= 14
template <class _Iter>
[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI
_LIBCPP_CONSTEXPR_SINCE_CXX17 reverse_iterator<_Iter> make_reverse_iterator(_Iter __i) {
  return reverse_iterator<_Iter>(__i);
}
#endif

template <class _Iter, bool __b>
struct __unwrap_iter_impl<reverse_iterator<reverse_iterator<_Iter> >, __b> {
  using _UnwrappedIter _LIBCPP_NODEBUG  = decltype(__unwrap_iter_impl<_Iter>::__unwrap(std::declval<_Iter>()));
  using _ReverseWrapper _LIBCPP_NODEBUG = reverse_iterator<reverse_iterator<_Iter> >;

  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ReverseWrapper
  __rewrap(_ReverseWrapper __orig_iter, _UnwrappedIter __unwrapped_iter) {
    return _ReverseWrapper(
        reverse_iterator<_Iter>(__unwrap_iter_impl<_Iter>::__rewrap(__orig_iter.base().base(), __unwrapped_iter)));
  }

  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _UnwrappedIter __unwrap(_ReverseWrapper __i) _NOEXCEPT {
    return __unwrap_iter_impl<_Iter>::__unwrap(__i.base().base());
  }
};

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___ITERATOR_REVERSE_ITERATOR_H