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

//
//  iterator_fwd.h
//  iterator
//
//  Created by Sam Jaffe on 2/18/17.
//

#pragma once

#include <cstdlib>
#include <iterator>

namespace iterator::recursive {
struct unbounded;
template <size_t N, size_t I = 1> struct bounded;
template <typename, typename = unbounded> class rimpl;
}

namespace iterator {
enum class category : unsigned char {
  single_pass, // input/output iterator, for example
  forward,
  bidirectional,
  random_access
};

struct sentinel_t;

// Iterator types
template <typename Iterator> class end_aware_iterator;
template <typename Iterator, typename Predicate> class filter_iterator;
template <typename OuterIterator> class joining_iterator;
template <typename Iterator> class unkeyed_iterator;
template <typename... Iterators> class zip_iterator;

template <typename Iterator>
using recursive_iterator = recursive::rimpl<Iterator>;
template <typename Iterator, std::size_t N>
using recursive_iterator_n = recursive::rimpl<Iterator, recursive::bounded<N>>;

template <typename CRTP, category C> class facade;

template <typename Iterator, typename CRTP,
          typename = typename std::iterator_traits<Iterator>::iterator_category>
class proxy;
}