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

//
//  count_if.h
//  stream
//
//  Created by Sam Jaffe on 4/2/23.
//

#pragma once

#include <stream/forward.h>

#include <stream/detail/identity.h>
#include <stream/detail/invoke.h>

namespace stream::ranges {
template <typename It, typename S, typename Pred,
          typename Proj = detail::identity>
auto count_if(It it, S end, Pred pred, Proj proj = {}) {
  size_t result = 0;
  for (; it != end; ++it) {
    if (detail::invoke(pred, *it, proj)) { ++result; }
  }
  return result;
}

template <typename Stream, typename Pred, typename Proj = detail::identity>
auto count_if(Stream const & stream, Pred pred, Proj proj = {}) {
  return count_if(stream.begin(), stream.end(), std::ref(pred), std::ref(proj));
}
}