Method destructor

muduo/base/ThreadLocal.h:45–51

 private:

  static void destructor(void *x)
  {
    T* obj = static_cast<T*>(x);
    typedef char T_must_be_complete_type[sizeof(T) == 0 ? -1 : 1];
    T_must_be_complete_type dummy; (void) dummy;
    delete obj;
  }

 private:
  pthread_key_t pkey_;