cpp-useful-iterators/include/iterator/cascade_iterator.h

#pragma once

#include <cstddef>

#include <iterator/concepts.h>
#include <iterator/detail/projection_tuple.h>
#include <iterator/detail/recursive_expander.h>
#include <iterator/end_aware_iterator.h>
#include <iterator/forwards.h>
#include <iterator/recursive_iterator.h>

namespace iterator {
template <typename It, typename Projs, typename MaxDepth>
class ProjectingRecursiveIterator;

template <typename It, typename... Projs, typename MaxDepth>
class ProjectingRecursiveIterator<It, detail::Projections<Projs...>, MaxDepth>
    : public RecursiveHelper<It, MaxDepth, detail::Projections<Projs...>>::type,
      public Facade<ProjectingRecursiveIterator<
          It, detail::Projections<Projs...>, MaxDepth>> {
public:
  using sentinel_type = sentinel_t;

public:
  ProjectingRecursiveIterator() = default;

  explicit ProjectingRecursiveIterator(Range auto & range, Projs... projs)
      : ProjectingRecursiveIterator(EndAwareIterator(range), projs...) {}

  explicit ProjectingRecursiveIterator(Range auto & range, MaxDepth,
                                       Projs... projs)
      : ProjectingRecursiveIterator(EndAwareIterator(range), projs...) {}

  explicit ProjectingRecursiveIterator(EndAwareIterator<It> iter, MaxDepth,
                                       Projs... projs)
      : ProjectingRecursiveIterator::RecursiveBase(iter, projs...) {}

  explicit ProjectingRecursiveIterator(EndAwareIterator<It> iter,
                                       Projs... projs)
      : ProjectingRecursiveIterator::RecursiveBase(iter, projs...) {}

  template <typename Ot>
  explicit ProjectingRecursiveIterator(EndAwareIterator<Ot> other,
                                       Projs... projs)
      : ProjectingRecursiveIterator(EndAwareIterator<It>(other), projs...) {}

  template <typename Ot>
  explicit ProjectingRecursiveIterator(EndAwareIterator<Ot> other, MaxDepth,
                                       Projs... projs)
      : ProjectingRecursiveIterator(EndAwareIterator<It>(other), projs...) {}
};

template <Range R, typename... Projs>
ProjectingRecursiveIterator(R, Projs...)
    -> ProjectingRecursiveIterator<iterator_t<R>, detail::Projections<Projs...>,
                                   bounded<sizeof...(Projs) + 1>>;

template <typename It, typename... Projs>
ProjectingRecursiveIterator(EndAwareIterator<It>, Projs...)
    -> ProjectingRecursiveIterator<It, detail::Projections<Projs...>,
                                   bounded<sizeof...(Projs) + 1>>;

template <Range R, typename... Projs, size_t N>
  requires(N > sizeof...(Projs))
ProjectingRecursiveIterator(R, bounded<N>, Projs...)
    -> ProjectingRecursiveIterator<iterator_t<R>, detail::Projections<Projs...>,
                                   bounded<N>>;

template <typename It, typename... Projs, size_t N>
  requires(N > sizeof...(Projs))
ProjectingRecursiveIterator(EndAwareIterator<It>, bounded<N>, Projs...)
    -> ProjectingRecursiveIterator<It, detail::Projections<Projs...>,
                                   bounded<N>>;

template <Range R, typename... Projs>
ProjectingRecursiveIterator(R, unbounded, Projs...)
    -> ProjectingRecursiveIterator<iterator_t<R>, detail::Projections<Projs...>,
                                   unbounded>;

template <typename It, typename... Projs>
ProjectingRecursiveIterator(EndAwareIterator<It>, unbounded, Projs...)
    -> ProjectingRecursiveIterator<It, detail::Projections<Projs...>,
                                   unbounded>;
}