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

  class iterator : facade<iterator> {
  public:
    using sentinal_type = Bound;

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

    T const & dereference() const { return value_; }
    void increment() const { ++value_; }
    bool at_end() const { return value_ == bound_; }
    std::ptrdiff_t distance_to(iterator const & other) const {
      return other.value_ - value_;
    }

  private:
    T value_;
    Bound bound_;
  };

private:
  T value_;
  Bound bound_;

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

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