#include <mutex>
class Y {
private:
  int some_detail;
  mutable std::mutex m;

  int get_detail() const
  {
    std::lock_guard<std::mutex> lock_a(m);
    return some_detail;
  }

public:
  Y(int sd) : some_detail(sd) {}

  friend bool operator==(Y const& lhs, Y const& rhs)
  {
    if (&lhs == &rhs)
      return true;
    int const lhs_value = lhs.get_detail();
    int const rhs_value = rhs.get_detail();
    return lhs_value == rhs_value;
  }
};

int
main()
{
}