template<typename It, typename OutIt, typename UnaryPredicate>
It move_if(It begin, It end, OutIt dst, UnaryPredicate pred)
{
  It last = end;
  while (begin != last) {
    if (pred(*begin)) {
      *dst++ = std::move(*begin);
      std::swap(*begin, *(--last));
    } else {
      ++begin;
    }
  }
  return last;
}