cpp-useful-iterators/include/iterator/recursive_iterator.hpp

//
//  recursive_iterator.hpp
//  iterator
//
//  Created by Sam Jaffe on 2/17/17.
//

#pragma once

#include <tuple>

#include "iterator_fwd.hpp"
#include "recursive/impl.hpp"
#include "recursive/traits.hpp"

namespace iterator {
  /**
   * @class recursive_iterator
   * @brief An iterator type for nested collections, allowing you to treat it as
   * a single-layer collection.
   *
   * In order to provide a simple interface, if an associative container is used
   * in the chain, the type returned by operator*() is a tuple. If multiple
   * associative containers are nested, then the tuple will be of the form
   * std::tuple<key1, key2, ..., keyN, value>. To avoid copies, and allow
   * editting of underlying values, the tuple contains references.
   *
   * @tparam Iterator The iterator type of the top-level collection.
   */
  template <typename Iterator>
  class recursive_iterator : public recursive::impl<Iterator> {
  public:
    using super = recursive::impl<Iterator>;
    using reference = decltype(*std::declval<super>());
    using value_type = std::remove_cv_t<std::remove_reference_t<reference>>;
    using pointer = decltype(std::declval<super>().operator->());
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::forward_iterator_tag;

  public:
    using super::super;
    recursive_iterator() = default;

    recursive_iterator & operator++() {
      (void)super::next();
      return *this;
    }

    recursive_iterator operator++(int) {
      recursive_iterator tmp{*this};
      (void)super::next();
      return tmp;
    }

    bool operator!=(recursive_iterator const & other) const {
      return !(static_cast<super const &>(*this) == other);
    }
  };

  /**
   * @class recursive_iterator_n
   * @copydoc recursive_iterator
   * This object has bounded recursive depth, so that it can be used to get
   * sub-collections, which may be used in other functions.
   *
   * For Example:
   * @code
   * using map_type = std::map<std::string, std::map<std::string,
   * std::vector<Data> > >;
   * ...
   * recursive_iterator_n<map_type::iterator, 2> iter{ ... };
   * std::vector<Data> & data = std::get<2>(*iter);
   * reload_data_from_file( std::get<1>(*iter), data );
   * @endcode
   *
   * @tparam N The maximum depth to recurse into the object
   */
  template <typename Iterator, std::size_t N>
  class recursive_iterator_n : public recursive::bounded_impl<Iterator, 1, N> {
  public:
    using super = recursive::bounded_impl<Iterator, 1, N>;
    using reference = decltype(*std::declval<super>());
    using value_type = std::remove_cv_t<std::remove_reference_t<reference>>;
    using pointer = decltype(std::declval<super>().operator->());
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::forward_iterator_tag;

  public:
    using super::super;
    recursive_iterator_n() = default;

    recursive_iterator_n & operator++() {
      (void)super::next();
      return *this;
    }

    recursive_iterator_n operator++(int) {
      recursive_iterator_n tmp{*this};
      (void)super::next();
      return tmp;
    }

    bool operator!=(recursive_iterator_n const & other) const {
      return !(static_cast<super const &>(*this) == other);
    }
  };
}

namespace std {
  template <std::size_t I, typename It>
  auto get(::iterator::recursive_iterator<It> const & iter) ->
      typename ::iterator::recursive::accessor<
          I, ::iterator::recursive_iterator<It>>::type {
    return iter;
  }

  template <std::size_t I, typename It, std::size_t N>
  auto get(::iterator::recursive_iterator_n<It, N> const & iter) ->
      typename ::iterator::recursive::accessor<
          I, ::iterator::recursive_iterator_n<It, N>>::type {
    static_assert(I < N, "Cannot get past bounding level");
    return iter;
  }
}

template <typename C>
auto make_recursive_iterator(C & collect)
    -> iterator::recursive_iterator<decltype(std::begin(collect))> {
  return iterator::recursive_iterator<decltype(std::begin(collect))>{
      make_end_aware_iterator(collect)};
}

template <typename C>
auto make_recursive_iterator(C const & collect)
    -> iterator::recursive_iterator<decltype(std::begin(collect))> {
  return iterator::recursive_iterator<decltype(std::begin(collect))>{
      make_end_aware_iterator(collect)};
}

template <std::size_t Max, typename C>
auto make_recursive_iterator(C & collect)
    -> iterator::recursive_iterator_n<decltype(std::begin(collect)), Max> {
  return iterator::recursive_iterator_n<decltype(std::begin(collect)), Max>{
      make_end_aware_iterator(collect)};
}

template <std::size_t Max, typename C>
auto make_recursive_iterator(C const & collect)
    -> iterator::recursive_iterator_n<decltype(std::begin(collect)), Max> {
  return iterator::recursive_iterator_n<decltype(std::begin(collect)), Max>{
      make_end_aware_iterator(collect)};
}