Boost C++ Libraries

// In header: <boost/histogram/indexed.hpp>

template<typename Histogram> 
class indexed_range {
public:
  // member classes/structs/unions

  // Pointer-like class to access value and index of current cell.

  class accessor {
  public:
    // member classes/structs/unions

    // Array-like view into the current multi-dimensional index.

    class index_view {
    public:
      // construct/copy/destruct
      index_view(const cache_item *, const cache_item *);

      // public member functions
      auto begin() const noexcept;
      auto end() const noexcept;
      auto size() const noexcept;
      int operator[](unsigned) const noexcept;
      int at(unsigned) const;
    };
    // construct/copy/destruct
    accessor(indexed_range &, value_iterator);

    // public member functions
    decltype(auto) operator *() const noexcept;
    decltype(auto) get() const noexcept;
    decltype(auto) operator->() const noexcept;
    int index(unsigned = 0) const noexcept;
    auto indices() const noexcept;
    template<unsigned N = 0> 
      decltype(auto) bin(std::integral_constant< unsigned, N > = {}) const;
    decltype(auto) bin(unsigned) const;
    double density() const;
  };

  struct cache_item {

    // public data members
    int idx;
    int begin;
    int end;
    int extent;
  };

  class range_iterator : public boost::iterator_adaptor< range_iterator, value_iterator, accessor, std::forward_iterator_tag, accessor >
  {
  public:
    // construct/copy/destruct
    range_iterator(indexed_range *, value_iterator) noexcept;

    // public member functions
    accessor operator *() const noexcept;

    // private member functions
    void increment() noexcept;
  };
  // construct/copy/destruct
  indexed_range(Histogram &, coverage);

  // public member functions
  range_iterator begin() noexcept;
  range_iterator end() noexcept;
};