A C++ iterator class that uses integer indices rather than pointers

buf_idx_iter.hpp

template<typename T>
class buf_idx_iter
{
public:
  using iterator_category = std::random_access_iterator_tag;
  using value_type = T;
  using difference_type = std::ptrdiff_t;
  using pointer = T*;
  using reference = T&;

  buf_idx_iter(pointer ptr = nullptr, size_t idx = 0) : m_ptr(ptr), m_idx(idx) {}

  friend auto operator<=>(const buf_idx_iter& lhs, const buf_idx_iter& rhs) {return lhs.m_idx <=> rhs.m_idx;};
  friend bool operator==(const buf_idx_iter& lhs, const buf_idx_iter& rhs) {return lhs.m_idx == rhs.m_idx;};
  friend difference_type operator-(const buf_idx_iter& lhs, const buf_idx_iter& rhs) { return lhs.m_idx - rhs.m_idx;}

  pointer operator->() const    { return m_ptr + m_idx; }
  reference operator*() const   { return *(m_ptr + m_idx); }

  buf_idx_iter& operator++() { ++m_idx; return *this; }
  buf_idx_iter& operator--() { --m_idx; return *this; }
  buf_idx_iter operator+(difference_type n) const { return buf_idx_iter(m_ptr, m_idx + n); }
  buf_idx_iter operator-(difference_type n) const { return buf_idx_iter(m_ptr, m_idx - n); }

private:
  pointer m_ptr;
  size_t m_idx;
};

template <typename V> buf_idx_iter<V> ibegin(std::vector<V>& vec){ return buf_idx_iter<V>(vec.data(), 0); }
template <typename V> buf_idx_iter<V> iend(std::vector<V>& vec) { return buf_idx_iter<V>(vec.data(), vec.size()); }