#include <iterator>
#include <istream>
#include <string>

class StreamedLines
{
public:
  struct Iterator
  {
  public:
    using iterator_category = std::input_iterator_tag;
    using difference_type   = void;
    using value_type        = std::string;
    using reference         = std::string&;
    using pointer           = std::string*;

    Iterator() = default;
    Iterator(StreamedLines *pStreamHolder)
      : m_pStreamHolder(pStreamHolder)
    {
      std::getline(m_pStreamHolder->m_in, m_currentLine);
    }

    Iterator(const Iterator &other) = default;
    Iterator(Iterator &&other)
    {
      m_pStreamHolder = other.m_pStreamHolder;
      m_currentLine = move(other.m_currentLine);
    }

    Iterator &operator=(const Iterator &other) = default;
    Iterator &operator=(Iterator &&other)
    {
      m_pStreamHolder = other.m_pStreamHolder;
      m_currentLine = move(other.m_currentLine);
      return *this;
    }

    std::string &operator*() { return m_currentLine; }
    std::string *operator->() { return &m_currentLine; }

    Iterator &operator++()
    {
      std::getline(m_pStreamHolder->m_in, m_currentLine);
      return *this;
    }
    Iterator operator++(int)
    {
      auto prev = *this;
      ++*this;
      return prev;
    }

    bool operator==(const Iterator &other)
    {
      return m_pStreamHolder == other.m_pStreamHolder
             || !m_pStreamHolder && other.m_pStreamHolder->m_in.eof()
             || !other.m_pStreamHolder && m_pStreamHolder->m_in.eof();
    }
    bool operator!=(const Iterator &other)
    {
      return !(*this == other);
    }

  private:
    StreamedLines *m_pStreamHolder;
    std::string m_currentLine;
  };

  StreamedLines(std::istream &in)
    : m_in(in)
  {
  }

  Iterator begin() { return Iterator(this); }
  Iterator end() { return Iterator(); }

private:
  std::istream &m_in;
};