C++ Primer, Fifth Edition

Message Copy-Assignment Operator

In common with most assignment operators, our Folder copy-assignment operator must do the work of the copy constructor and the destructor. As usual, it is crucial that we structure our code to execute correctly even if the left- and right-hand operands happen to be the same object.

In this case, we protect against self-assignment by removing pointers to this Message from the folders of the left-hand operand before inserting pointers in the folders in the right-hand operand:

Message& Message::operator=(const Message &rhs){    // handle self-assignment by removing pointers before inserting them    remove_from_Folders();   // update existing Folders    contents = rhs.contents; // copy message contents from rhs    folders ...