C++ Primer, Fifth Edition

Managing the Discriminant and Destroying the string

The assignment operators will set tok and assign the corresponding member of the union. Like the destructor, these members must conditionally destroy the string before assigning a new value to the union:

Token &Token::operator=(int i){    if (tok == STR) sval.~string(); // if we have a string, free it    ival = i;                       // assign to the appropriate member    tok = INT;                      // update the discriminant    return *this;}

If the current value in the union is a string, we must destroy that string before assigning a new value to the union. We do so by calling the string destructor. Once we’ve cleaned up the string member, we assign the given value to the member that ...