Cpp Coding Standards/VIRTUAL
Contents
Hierarchies of Virtual Classes
These items refer to class hierarchies where the base class is virtual and the derived classes are intended to be used – at least sometimes – via pointers or references to the base class.
Summary
Liskov
Always follow the Liskov Substitution Principle: Everything a client can do with a base class, it must be able to do with each derived class as well.
Instantiation
In an inheritance tree of virtual classes, instantiate only the leaves. Make all other classes either abstract or their constructors protected, so instantiation is impossible.
Overrides
Do not give overrides of a virtual function stronger preconditions or weaker postconditions.
Give them the same default values.
Use the “virtual” keyword also on all overrides.
RightDestructor
All virtual classes need a virtual destructor. If the class can not be instantiated, the destructor may be inline, else it has to be non-inline. Non-virtual mix-in classes need a protected destructor.
NonVirtualInterfaces
If a class has more than one parallel derived class, use the Non Virtual Interface idiom.
SafeCopying
If a virtual class needs to be copied via references to a base class, disable the copy constructor and operator=() in the base classes and implement the clone() idiom instead.
