cpp-lazy-stream/include/stream/algorithm/size.h

//
//  size.h
//  stream
//
//  Created by Sam Jaffe on 3/30/23.
//

#pragma once

#include <stream/detail/traits.h>

namespace stream::ranges {
template <typename It, typename S> std::ptrdiff_t distance(It it, S end) {
  if constexpr (detail::is_sized_sentinel_v<It, S>) {
    return end - it;
  } else {
    std::ptrdiff_t accum = 0;
    for (; it != end; ++it) {
      ++accum;
    }
    return accum;
  }
}

template <typename Stream> size_t size(Stream const & stream) {
  if constexpr (detail::has_size_v<Stream>) {
    return stream.size();
  } else {
    return distance(stream.begin(), stream.end());
  }
}

template <typename Stream> bool empty(Stream const & stream) {
  if constexpr (detail::has_empty_v<Stream>) {
    return stream.empty();
  } else {
    return stream.begin() == stream.end();
  }
}
}