Class to save and restore ostream state in C++, to make floating point format management a bit saner

ostream_state.cpp

class ostream_state {
  std::ostream::fmtflags flags;
  std::streamsize precision = 6;

 public:
  class Save {
    friend ostream_state;

    friend std::ostream& operator<<(std::ostream& out, const Save& save) {
      save.save(out);
      return out;
    }

    ostream_state& state;

    Save(ostream_state& state) : state(state) {}

    void save(const std::ostream& out) const {
      state.flags = out.flags();
      state.precision = out.precision();
    }
  };

  Save save() { return Save(*this); }

  class Restore {
    friend ostream_state;

    friend std::ostream& operator<<(std::ostream& out, const Restore& restore) {
      restore.restore(out);
      return out;
    }

    const ostream_state& state;

    Restore(const ostream_state& state) : state(state) {}

    void restore(std::ostream& out) const {
      out.flags(state.flags);
      out.precision(state.precision);
    }
  };

  Restore restore() { return Restore(*this); }
};