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 {
struct sentinel_t;

// Iterator types
template <typename It> class CaptureIterator;
template <typename It> class EndAwareIterator;
template <typename It> class EnumerateIterator;
template <typename It, typename Pred> class FilterIterator;
template <typename OIt> class JoinIterator;
template <typename It> class ValuesIterator;
template <typename... Its> class ZipIterator;

struct unbounded {};
template <size_t N>
  requires(N > 0)
struct bounded {};

template <typename It, typename MaxDepth = unbounded> class RecursiveIterator;
template <typename It, size_t N>
using RecursiveIteratorN = RecursiveIterator<It, bounded<N>>;
template <typename It, typename Projs, typename MaxDepth>
class ProjectingRecursiveIterator;

template <typename CRTP> class Facade;

template <typename It, typename CRTP,
          typename = typename std::iterator_traits<It>::iterator_category>
class Proxy;
}