Chapter 4, Swap - From Simple to Subtle

1. The swap function exchanges the state of the two objects. After the swap call, the objects should remain unchanged, except for the names they are accessed by.
2. Swap is usually employed in programs that provide commit-or-rollback semantics; a temporary copy of the result is created first, then swapped into its final destination only if no errors were detected.
3. The use of swap to provide commit-or-rollback semantics assumes that the swap operation itself cannot throw an exception or otherwise fail and leave the swapped objects in an undefined state.
4. A non-member swap function should always be provided, to ensure that the calls to non-member swap are executed correctly. A member swap function can also be provided, for two reasons—first, it is the only way to swap an object with a temporary, and second, the swap implementation usually needs access to the private data members of the class. If both are provided, the non-member...