Virtual Functions & Multiple Inheritance in Visual FoxPro

• Microsoft Visual FoxPro for Windows, version 3.0

SUMMARY

Multiple inheritance or the ability to create a single subclass from several base classes at once is not supported in Visual FoxPro version 3.0.

Each subclass can have only one, single immmediate ancestor. However derived subclasses can be used as base classes themselves for subsequent derived classes, which may override or add methods and properties

MORE INFORMATION

C++ programmers use virtual functions to create abstract classes. In C++, member functions are bound at compile time unless specifically classified as virtual by using the key word 'virtual' in the declaration of the function. Virtual functions often do not have any code associated with them and are present only to provide type compatibility with variable assignment.

For example, an array may be declared as an array of pointers to a base class type with a virtual function. It is then possible to assign each element a pointer for a given subclass of the base class without generating a compiler error. Derived classes from the base class define code that is to be used for the particular object. The reason virtual functions are needed in C++ and not in Visual FoxPro is because C++ is a strongly typed language and Visual FoxPro is not. With Visual FoxPro, you can have an array hold references to different object types in its elements.

REFERENCES

"Data abstraction and structures using C++" Mark R. Headington and David D.

 Riley, D.C. Heath and Company 1994 ISBN 92-75664