,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,*,*,Five Fundamental Patterns,Working with Classes and Interfaces,Jim Fawcett,CSE776 Design Patterns,Summer 2004,Reference,Working with Classes and Interfaces,five fundamental patterns,Dirk,Riehle,C+Report,March 2000.,A Pattern Language for OOD,Small patterns,Design idioms,Good practice,Pattern language,Coordinated set of patterns,One focused topic area,Individual patterns often stated in abbreviated style,Simple Class Pattern,Problem:,You need to design and implement a concept.,Context:,One implementation is sufficient,no other is needed.,Changes to implementation may affect clients.,You want to make it as simple as possible,but not simpler.,Solution:,Implement the concept as a single class,Design by Primitives,Problem:,You need to implement a class.,Context:,You expect to evolve the class.,You want it to be easy to add new member functions.,You want to avoid a fragile class in which changes to a function affect many other functions.,You want to make it as simple as possible,but not simpler.,Solution:,Separate more complex non-,primative,member functions from primitive member functions.,Determine the primitive member functions that best help implement the class.,Implement non-primitive member functions using primitive member functions.,Interface Class,Problem:,You need to design and implement a concept with different implementations.,Context:,You want to give clients freedom of choice:,for selecting an implementation.,to not care about the implementation.,You want to change implementations without affecting clients.,You want to introduce new implementations without making clients notice.,You want to separate implementations from their clients.,You want to make it as simple as possible,but not simpler.,Solution:,Determine the functionality of the concept separately from its implementations.,Represent the functionality as an interface class(only pure virtual functions).,Make implementation classes inherit and implement the interface class.,Abstract Base Class,Problem:,You need to ensure identical behavior of concept implementations where functionality is identical,and provide different behavior,where functionality is different.,Context:,You want to avoid redundant code.,You want to ease adding other implementations.,You want to make it as simple as possible,but not simpler.,Solution:,Separate variant functionality of the implementations from invariant functionality.,Implement the invariant part as shared functionality in an abstract base class.,Declare the variant part in the abstract base class using pure virtual functions.,Make implementations subclasses of the abstract base class that implement the variant part.,Narrow Interface Class,Problem:,You need to minimize effort to introduce new subclasses of an abstract base class.,Context:,You are using an abstract base class with many pure virtual member functions.,You expect existing subclasses to evolve and new subclasses to enter the system.,You want to make it as simple as possible,but not simpler.,Solution:,Reduce the number of pure virtual member,fuctions,to it minimum by using design by primitives.,Provide default implementations of primitives were possible.,Implement all non-primitive member functions using primitives.,