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Back to Outline 19 - Design Patterns for SaaS. On to Outline 21 - Course Wrapup.

Summary

Related Pages

We continue our exploration of good program design.

Overview

• Design Patterns.
• The GoF List.
• Some Questions.
• SOLID.

Administrivia

Design Patterns

• Inspired by C. Alexander's work on Architecture, A Pattern Language.
• Leading OO-programmers/designers looked at common software architecture tasks/problems and came up with a taxonomy of common solutions to those problems.
• Valuable in (at least) two ways
  • For novice programmers, provides better approaches to tasks that they don't realize are old.
  • For experienced programmers, provides a language to talk about approaches.
• There are growing movements to write "patterns" (and "anti-patterns") for many different classes of problems. There are even teaching patterns.
• Most folks at Grinnell believe that you apply patterns loosely; they are intended as a way to help you think, rather than strict strategies.
• Some patterns will feel obvious to you.
  • Some have always been part of functional languages
  • Some are now incorporated into language design

Some Questions

GoF Patterns

Creational

• Abstact Factory
• Factory Method
• Singleton
• Prototype
• Builder

Structural

• Adapter
• Proxy
• Facade
• Bridge
• Decorator
• Composite
• Flyweight

Behavioral

• Template Method
• Strategy
• Observer
• Iterator
• Visitor
• State
• Chain of Responsibility
• Mediator
• Interpreter
• Command

SOLID Principles

Intended as a mechanism for thinking about class design. Five basic principles.

• Single Responsibility - Do one thing well.
• Open/Closed - Open for extension, closed against modification.
• Liskov Substitution Principle - T's subclasses follow the interface
• Interface Segregation
• Dependency Inversion