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c++inheritanceterminology

Proper inheritance

What is meant by proper inheritance?

Solution

  • I would like to add to what Justin and Baxter said.

    The term proper inheritance is not really well-defined. Properly using inheritance is quite a subjective issue...

    Consider the following example:

    • An interface: Bird
    • A concrete class: Ostrich

    Should Ostrich inherits from Bird ? From a zoological point of view it makes sense, but from a Computer Science point of view... not so much. If Bird has a fly method, then how am I supposed to handle this in Ostrich::fly :x ?

    There is somewhat of a war in the CS community. Indeed you'll regularly see books where Circle inherits from Ellipse (or the other way around) when it doesn't really makes sense from a CS point of view.

    So my own little definition:

    Considering that the interface defines precise semantics for each of its methods, a concrete class should only inherit from the interface if the implementation of each of the method matches the semantics specified.