inheritance, a.k.a. subclassing


two is-a's and a has-a
  is-a (instance of)
    describes instance-class relationship
    e.g. Martin is an instance of human being
    e.g. ticketingQ is an instance of CarQueue

  is-a (kind of)
    describes class-class relationship
    e.g. professor is a kind of human being
    e.g. ColorPoint is a kind of Point

  has-a (contains)
    describes class-instance relationship
    e.g. human being has a brain (usually)
    e.g. FerrySim has a CarQueue (two, in fact)

We know how to express "is-a instance of" and "has-a" in
C++, but not "is-a" kind of yet.  Our feature language
feature is "inheritance" or "subclassing".


ways of thinking about inheritance

  An instance of a derived class is/has everything that an
  instance of its base clase is/has and more.*
  
  *caveat:  If a var. or method is private in the base class, 
   it cannot be referenced in the derived class.

  A subclass describes a specialization of its superclass.


levels of hiding/protection
  public
    can be referenced by any code (client, implementation, etc.)
  protected
    can be referenced by implementation of this class and 
    derived classes
  private
    can *only* be referenced by implementation of this class


initializer list
  means of initializing private member variables of base class


method overriding
  derived class defines method with same name and parameter
    types (number, type and order) as method in base class
  overriding overriding using :: (class scope operator)
  not the same as overloading, which is independent of inheritance


examples
  Point, ColorPoint (Slide Set Q) 
  contrived, self-documenting example:  Base and Derived


other remarks...  What have we learned?
  Use the debugger and asserts when coding with pointers.
  Successful compilation is half the battle.
  Syntax errors are inexcusable.
  Think more, code less.
  Read instructions carefully!