Why do we actually need Private or Protected inheritance in C++?

Question

In C++, I can\'t think of a case in which I would like to inherit private/protected from a base class:

class Base;
class Derived1 : private Base;
class Deri         


        

Answer 1

Public inheritance models IS-A.
Non-public inheritance models IS-IMPLEMENTED-IN-TERMS-OF.
Containment models HAS-A, which is equivalent to IS-IMPLEMENTED-IN-TERMS-OF.

Sutter on the topic. He explains when you'd choose non-public inheritance over containment for implementation details.