cpp-lazy-stream/include/stream/iota_view.h

//
//  iota_view.h
//  stream
//
//  Created by Sam Jaffe on 3/29/23.
//

#pragma once

#include <iterator/facade.h>

namespace stream::ranges {
template <typename T, typename Bound>
class iota_iterator : public facade<iota_iterator<T, Bound>> {
public:
  using sentinal_type = Bound;

  iota_iterator() = default;
  iota_iterator(T value, Bound bound) : value_(value), bound_(bound) {}

  T const & dereference() const { return value_; }
  void increment() { ++value_; }
  bool at_end() const { return value_ == bound_; }
  // Some weird bug in dependent template instantiation???
  bool equal_to(iota_iterator const & other) const {
    return value_ == other.value_;
  }
  std::ptrdiff_t distance_to(iota_iterator const & other) const {
    return other.value_ - value_;
  }

private:
  T value_;
  Bound bound_;
};

template <typename T, typename Bound> struct iota_view {
public:
  constexpr static inline bool has_size_v = std::is_constructible_v<T, Bound>;

private:
  T value_;
  Bound bound_;

public:
  iota_view(T value, Bound bound) : value_(value), bound_(bound) {}

  auto begin() const { return iota_iterator(value_, bound_); }
  auto end() const {
    if constexpr (has_size_v) {
      return iota_iterator(bound_, bound_);
    } else {
      return bound_;
    }
  }

  bool empty() const { return begin().at_end(); }
  auto size() const -> std::enable_if_t<has_size_v, size_t> {
    return begin().distance_to(end());
  }
};
}

namespace stream::ranges::views {
template <typename T, typename Bound> auto iota(T value, Bound bound) {
  return iota_view(value, bound);
}
}

MAKE_ITERATOR_FACADE_TYPEDEFS_T(stream::ranges::iota_iterator);