iterator.hpp

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#pragma once
 
#include <iterator>
 
#if YACLIB_CXX_STANDARD < 20 ||                                                                                        \
  (defined(__clang__) && __clang_major__ <= 12)  // std::counted_iterator not implemented in stl
 
namespace yaclib::detail {
 
struct DefaultSentinel {};
 
template <typename It>
class counted_iterator {
 public:
  using iterator_category = typename std::iterator_traits<It>::iterator_category;
  using value_type = typename std::iterator_traits<It>::value_type;
  using difference_type = typename std::iterator_traits<It>::difference_type;
  using pointer = typename std::iterator_traits<It>::pointer;
  using reference = typename std::iterator_traits<It>::reference;
 
  counted_iterator() : _it{}, _n{0} {
  }
 
  counted_iterator(It it, difference_type n) : _it{it}, _n{n} {
  }
 
  reference operator*() const {
    return *_it;
  }
 
  pointer operator->() const {
    return _it.operator->();
  }
 
  counted_iterator& operator++() {
    ++_it;
    --_n;
    return *this;
  }
 
  counted_iterator operator++(int) {
    auto tmp = *this;
    ++(*this);
    return tmp;
  }
 
  bool operator==(const counted_iterator& rhs) const {
    return _it == rhs._it;
  }
 
  bool operator!=(const counted_iterator& rhs) const {
    return !(*this == rhs);
  }
 
 private:
  It _it;
  difference_type _n;
 
  friend bool operator==(const counted_iterator<It>& lhs, [[maybe_unused]] DefaultSentinel rhs) {
    return lhs._n == 0;
  }
 
  friend bool operator==(DefaultSentinel lhs, const counted_iterator<It>& rhs) {
    return rhs == lhs;
  }
 
  friend bool operator!=(const counted_iterator<It>& lhs, DefaultSentinel rhs) {
    return !(lhs == rhs);
  }
 
  friend bool operator!=(DefaultSentinel lhs, const counted_iterator<It>& rhs) {
    return !(lhs == rhs);
  }
 
  friend difference_type operator-(const counted_iterator<It> lhs, [[maybe_unused]] DefaultSentinel rhs) {
    return -lhs._n;
  }
 
  friend difference_type operator-(DefaultSentinel lhs, const counted_iterator<It> rhs) {
    return -(rhs - lhs);
  }
};
 
}  // namespace yaclib::detail
 
namespace yaclib_std {
 
using default_sentinel_t = yaclib::detail::DefaultSentinel;
 
inline constexpr default_sentinel_t default_sentinel{};
 
using yaclib::detail::counted_iterator;
 
}  // namespace yaclib_std
 
#else
 
namespace yaclib_std {
 
using std::default_sentinel_t;
 
inline constexpr default_sentinel_t default_sentinel{};
 
using std::counted_iterator;
 
}  // namespace yaclib_std
 
#endif