Designing SOLID, Patterned Code

Most developers who have been in industry for a while will have heard about the SOLID principles, some may even have been asked interview questions about them, but far fewer fully understand them. The SOLID principles, understood and judiciously applied, result in code that is easier to understand, maintain, and test. With that end in mind we will cover each of the SOLID principles striving to understand them and their relationship to design patterns. In this session we’ll get our hands dirty designing a command line application that allows new commands with their associated switches and options to be easily added, parsed, and validated.

Transcript

1. Designing SOLID, Patterned Code By Kaleb Pederson
2. Foundational Principles
3. “BAD” Software?
4. RIGIDity Image Courtesy: http://www.medicalexpo.com/prod/dicarre/product-103728-672472.html
5. Image Courtesy: http://teresanfischer.blogspot.com/2012/02/salon-international-2012-and-precarious.html FRAGILity
6. IMMOBILity Image Courtesy: http://thequestionconcerningtechnology.blogspot.com/2012/10/on-immovable-technologies.html
7. Viscos ity Image Courtesy: https://3docean.net/item/viscous-fluid/15365560
8. Needless Complexity Image Courtesy: https://www.laserfiche.com/simplicity/how-complexity-makes-it-harder-to-use/
9. 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Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition 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Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Repetition Needless Needless Repetition
11. Bob & Micah Martin’s Agile Principles, Patterns, and Practices in C#
12. “GOOD” Software?
13. “GOOD” Software = !(BAD Software)
14. SOLID principles
15. Single Responsibility Principle Open-Closed Principle Liskov Substitution Principle Interface Segregation Principle Dependency Inversion Principle - By Uncle Bob Martin
17. SRP?
18. def Single Responsibility Principle (SRP): “A class should have only one reason to change.”
19. SRP Example
21. def Open Closed Principle (OCP): “...open for extension but closed for modification”
22. I.E. “The behaviors of an object that are expected to change should be able to change without modifying the object itself.”
23. Password? • 1 upper case character • 1 lower case character • 1 number • 2 symbols
26. def Liskov Substitution Principle (LSP):
27. def Liskov Substitution Principle (LSP): “If it can be assumed, it will be, but don’t violate assumptions.”
28. LSP ?Counter? Example Rectangle Square
29. LSP Example «IShape» +Draw() Rectangle Square
30. LSP Counter Example Rectangle +Width +Height Square
32. Contravariance LSP Func Reqs: One
33. Covariance LSP Func Reqs: Two
34. new Exception LSP Func Reqs: Three
35. new Preconditions LSP Behavioral Reqs: 1
36. del Postconditions LSP Behavioral Reqs: 2
37. Enforce Invariants LSP Behavioral Reqs: 3
38. Hyrum’s Law ...all observable behaviors of your system will be depended on by somebody.
40. def Interface Segregation Principle (ISP): “No client should be forced to depend on methods it does not use.”
41. Role Interfaces «IParent» «IChild» +Method() ?
44. def Dependency Inversion Principle (ISP) [1/2]: «Low Level» «Abstractions» «High Level»
45. def Dependency Inversion Principle (ISP) [2/2]: «Low Level» «Abstractions» «High Level»
46. Invert ?pe
47. PasswordValidator Main LengthRule NumberRule
48. PasswordValidator Main LengthRule NumberRule 2 ... 1 ...
49. PasswordValidator Main LengthRule NumberRule 2 ... 1 ... IOC
50. «IPasswordValidator» Main LengthRule NumberRule PasswordValidator «IPasswordRule» App.Validation App.Contracts
51. Domain
52. «IPasswordValidator» Main LengthRule NumberRule PasswordValidator «IPasswordRule» App.Validation
53. Source Code URL https://github.com/kalebpederson/sample-solid-cli
54. Credits • Colors via Miss_Anthropy@ColourLovers.com • SOLID posters from LosTechies.com on MSDN: https://blogs.msdn.microsoft.com/cdnde vs/2009/07/15/the-solid-principles-explai ned-with-motivational-posters/ • Others as posted on slides
55. References • Agile Principles, Practices, and Patterns by Robert Martin and Micah Martin • 99 Bottles of OOP by Sandi Metz and Katrina Owen • “Clean Code: SOLID Principles” by Uncle Bob on CleanCoders.com