json-validator/include/jvalidate/compat/enumerate.h

#pragma once

#if __cplusplus >= 202302L
#include <ranges>
#if __cpp_lib_ranges_enumerate >= 202302L
#define JVALIDATE_USE_STD_RANGES_ENUMERATE
#endif
#endif

#ifdef JVALIDATE_USE_STD_RANGES_ENUMERATE
namespace jvalidate::detail {
using std::ranges::views::enumerate;
}
#else

#include <iterator>
#include <utility>

#include <jvalidate/detail/deref_proxy.h>

namespace jvalidate::detail {

/**
 * @brief A replacement for std::ranges::views::enumerate in C++20 (as enumerate
 * is a C++23 feature).
 * Much like python's enumerate() function, this is an iterator adapter that
 * attaches the "index" of the iteration to each element - incrementing it as
 * we go.
 */
template <typename It> class enumurate_iterator {
public:
  using traits_t = std::iterator_traits<It>;

  using value_type = std::pair<size_t, typename traits_t::value_type>;
  using reference = std::pair<size_t const &, typename traits_t::reference>;
  using pointer = DerefProxy<reference>;
  using difference_type = typename traits_t::difference_type;
  using iterator_category = std::forward_iterator_tag;

private:
  size_t index_ = 0;
  It iter_;

public:
  enumurate_iterator(It iter) : iter_(iter) {}

  reference operator*() const { return {index_, *iter_}; }
  pointer operator->() const { return operator*(); }

  enumurate_iterator & operator++() {
    ++index_;
    ++iter_;
    return *this;
  }

  friend bool operator==(enumurate_iterator<It> rhs, enumurate_iterator<It> lhs) {
    return rhs.iter_ == lhs.iter_;
  }
  friend bool operator!=(enumurate_iterator<It> rhs, enumurate_iterator<It> lhs) {
    return rhs.iter_ != lhs.iter_;
  }
};

template <typename C> auto enumerate(C && container) {
  struct {
    auto begin() const { return enumurate_iterator(c.begin()); }
    auto end() const { return enumurate_iterator(c.end()); }

    C c;
  } rval{std::forward<C>(container)};
  return rval;
}
}
#endif