Intro to Inheritance

• This is chapter 10.
  • You should read this.
• We learn how to implement an is-a relationship.
• A frog is a animal
  • In this case the animal is a base class.
  • The frog is a derived class.
• The base class is the most generic
  • Methods and data in the base class apply to all derived classes.
  • We can replace functionalitity
  • We can add functionality
  • But we should not remove functionality.
    • If we need to do this, it was not a member of the generic base class.
• A word of caution, what we think of as inheritence in the real world only goes so far.
  • The animal and frog relationship depends on the abstraction.
  • This gets tricky.
• I plan to develop the idea of a 2d game board
  • the board has the following operations
    • Rows, Cols
    • Move
    • [row,col]
  • I have at least two different types of boards.
    • periodic boundary conditions
    • fixed bondary conditions.
  • I want to share all of the memory allocation routines
  • I want a common interface
  • But I want to deal with "out of bounds" differently in each.
• I could just
  • Implement the animal class.
  • Copy the code to the frog class and change it.
• This creates several problems however
  • The classes are no longer related via code,
    • I have duplicate code.
    • I need to remember to update the code in both (all) places.
  • The compiler doesn't know about the relationship between these, so I can't employ polymophism
• Syntax

  • class BaseT {
    };
    
    class DerivedT : public BaseT {
    };
            

• The dervied class
  • HAS all of the base class' methods and data.
  • Has direct access to all public and potected methods and data.
  • Has indirect access (throught the base class public and protected methods) to the base class' private data and methods.
• To a client passed a reference or a pointer to the base class It can be either
  • We will discuss the mechanism later, but believe this for now.
  • dynamic_cast< dest type>(expression)
    • Converts pointers and references from one type to another.
    • reference.
    • It is important that the class has a virtual function.