Being more complex than single inheritance, Multiple inheritance (MI) can lead to ambiguity issues and to the need for virtual inheritance, the latter of which imposes costs in size, speed, and complexity of initialization and assignment, so it’s more practical to make “empty” virtual base classes.

Private inheritance means is-implemented-in-terms-of. It is usually inferior to composition, but it makes sense when a derived class needs access to protected base members or needs to redefine inherited virtual functions. For library developers who strive to minimize object sizes, it also offers the ability of empty base optimization.

In the application domain, composition means has-a. In the implementation domain, it means is-implemented-in-terms-of.

Defaul parameter values are statically bound, while virtual function - the only functions we should be overriding - are dynamically bound.

A generalized basic rule from item 7.