⎗ ✓ 1 2 3 4 5 6 7 8 9 10 11 12 13class Out { static mutex mtx; public: Out() = default; Out(const Out&) = delete; Out& operator=(const Out&) =delete; template<class T> ostream& operator<<(const T& data){ lock_guard<mutex> lock(mtx); return cout << data; } };