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SOLID Agile Software Design Principles- C#

A Consulting Division Presentation

Month Date, 2006 — © — All Rights Reserved

Tim Star

tstar@intertech.comhttp://www.intertech.com/Blog/

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Intertech

Training Training through hands-on, real

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Our Company Over 35 awards for growth,

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Principal Consultant / .Net Architect Writing Software over 20 Years 5 X Microsoft MVP Visual Studio ALM Ranger – 6 years MCPD Enterprise App Development 3.5/4.0 Framework MCTS WPF/TFS MCP – VS ALM and Testing with MTM MCT

Experience – Tim Star

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Single Responsibility Principle (SRP)Open Closed Principle (OCP)Liskov Substitution Principle (LSP)Interface Segregation Principle (ISP)Dependency Inversion Principle (DIP)

Simple Examples

Agenda

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We want the “ability to develop software quickly, in the face of rapidly changing requirements”. – “Uncle Bob” Martin

Flexibility Maintainability Testability

Motivation

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Every class should have a single responsibility, and that responsibility should be entirely encapsulated by the class. All its services should be narrowly aligned with that responsibility

Martin defines a responsibility as a reason to change, and concludes that a class or module should have one, and only one, reason to change.

Single Responsibility Principle

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Benefits Highly cohesive classes are easier to maintain Simplifies testing

Drawbacks More classes tends to add complexity

Code Smells Class with 1000’s of Lines of Code Class with Many unrelated or loosely related Methods

SRP Continued

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Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification

Open Closed Principle

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Benefits Working code stays working Changes are achieved via new code

Drawbacks Tends to add complexity

Code Smells Switch logic If/Then/Else TypeOf()

OCP Continued

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Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program

Liskov Substitution Principle

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Benefits Reuse Maintainable Robust

Drawbacks Code Smells

Method Hiding Not Implemented Exception Covariance object[] array = new String[10]; Derived Class Violates Reasonable Assumptions

LSP Continued

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Many client-specific interfaces are better than one general-purpose interface

Interface Segregation Principle

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Benefits Less Code Lower Test Impact with Change

Drawbacks Adds Complexity – Can “Overdo It”

Code Smells Long Interfaces Interfaces with Unrelated Concerns

ISP Continued

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Depend upon Abstractions. Do not depend upon concretions.

Dependency Inversion Principle

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Benefits Maintainable / Resilient To Change Testable

Drawbacks Adds Complexity – Can “Overdo It”

Code Smells New()

DIP Continued

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Demo

SOLID

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Great resource: “Agile Principles, Patterns, and Practices in C#”

http://www.butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

http://en.wikipedia.org/wiki/Solid_(object-oriented_design)

Reference

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Next Oxygen Blasts July 30th

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Upcoming Webinars and Training

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Questions or Feedback?Patrick Schaber – pschaber@Intertech.com

Thank You