Introduction to Inheritance

• He starts the section with a semi-example.
  • I would like to make it more concrete.
  • This example is good
    • It shows the power of inheritance
      • Code reuse
      • Code Extension
      • Code Replacement.
  • This example is bad
    • It is sort of a non-cooperating version
    • So some things are not done "right"
• I have built a Container class.
  • It is rather silly, it is just a wrapper for a vector of ints.
• It does have an interesting feature or two however.
  • I used an initializer list.
  • I also used a compiler generated default constructor. (Why?)
  • I don't like the data access function, but we need to get to exceptions to do this correctly.
  • I did overload the [] operator.
    • There are two cases of this.
    • One is used for const objects.
    • The other is not.
    • Notice they both return a reference.
    • But one is const and the other is not.
      • The const is what makes a difference in the function signature.
      • We will see in the derived class the difference is important.
    • By the way, the [] is discussed on page 486
      • It always takes a single argument.
      • It really should return a value.
        • This is not required.
      • However there is a fairly standard rule that says "make things behave the same".
        • And what does the [] operator do?
  • Have a look at Container.h and Container.cpp
• I have created a derived class from the base class.
  • Note, I do not need access to the implementation code. (I can move that to another directory if you wish.
  • This class demonstrates the major abilities of inheritance.
  • We employ the underlying data structure and most methods.
  • We override some of the existing methods.
  • We augment the class by providing new methods.
  • We disable existing methods.
• The new class is an EvenContainer
  • Like the base class, it holds multiple integers.
  • Unlike the base class, it will only hold even integers.
• To accomplish this I needed to
  • Modify the constructor.
  • Modify or replace the insertion operator
  • Delete the variable [] operator.
• Have a look at EvenContainer.h and EvenContainer.cpp
• Notice a cool thing in main.cpp.
  • Even though PrintContainer takes a Container, it can also take an Event Container.
    • It prints just fine.
    • But unfortunately, it can chagne the container too.
    • This is an example of slicing
      • We essentually passed in the base class.
      • So the modifications were removed.
      • We will deal with this later.