To disallow copying or assigning a class it\'s common practice to make the copy constructor and assignment operator private. Both Google and Qt have macros to make this eas
See Boost.Utility, specifically boost::noncopyable. It's not a macro but a base class with private copy and assignment. It prevents the compiler from generating implicit copy and assignment in derived classes.
edit: Sorry, this was not an answer to the original question. By the way, boost::noncopyable uses a const reference as return type for the assignment operator. I was under the impression that the type of the return value doesn't matter since it's not supposed to be used. Still, making the operator private doesn't prevent usage inside the class or friends in which case a non-usual return type (like void, a const reference, etc) might lead to compilation errors and catch additional bugs.