Item 34: Differentiate Between Inheritance of Interface and Inheritance of Implementation

Consider: Pure virtual (with or without implementation), simple (impure) virtual, and non-virtual function.

• Pure virtual: Inherit interface only (and if it comes with an implementation, the derived class may explicitly choose to inherit the implementation)
  • Pure virtual must be redeclared in (direct) derived class (you may use this to force derived class explicitly choose the inherit implementation)
• Simple virtual: Inherit interface and implicitly inherit implementation
• Non-virtual: Inherit interface and a mandatory implementation
  • You may think of this as an invariance over specialization (all derived class will maintain this invariance)