C++ Coding Standards: 101 Rules, Guidelines, and Best Practices

37. Public inheritance is substitutability. Inherit, not to reuse, but to be reused

Summary

Know what: Public inheritance allows a pointer or reference to the base class to actually refer to an object of some derived class, without destroying code correctness and without needing to change existing code.

Know why: Don’t inherit publicly to reuse code (that exists in the base class); inherit publicly in order to be reused (by existing code that already uses base objects polymorphically).

Discussion

Despite two decades of object-oriented design knowledge, the purpose and practice of public inheritance are still frequently misunderstood, and many uses of inheritance are flawed.

Public inheritance must always model “is-a” (“works-like-a”) according ...