Solid principles presentation on GibDevs meetup by Vytautas Dagilis on 22/08/2019

1. SOLID PRINCIPLES
SOLID CODE
Vytautas Dagilis

2. “EMPLOYEES WHO WERE NEVER
COMPETENT ARE PROMOTEDTO
MANAGEMENTTO LIMIT THE
DAMAGETHEY CAN DO”
© Scott Adams

3. ROBERT C. MARTIN
a.k.a. Uncle Bob
https://blog.cleancoder.com

4. WHY DOES GOOD CODE
MATTER?

5. WE DID NOT GET INTHE BUSINESS
OF SOFTWARETO KILL PEOPLE;
BUT WE ARE KILLING PEOPLE
© Uncle Bob

6. WHO WRITES BAD CODE?

7. WHAT IS GOOD CODE!?

8. SINGLE RESPONSIBILITY
Every module or class should have responsibility over a single
part of the functionality provided by the software

9. class Post
{
void CreatePost(Database db, string postMessage)
{
try
{
db.Add(postMessage);
}
catch (Exception ex)
{
db.LogError("An error occured: ", ex.ToString());
File.WriteAllText("LocalErrors.txt",ex.ToString());
}
}
}

10. class Post
{
private ErrorLogger errorLogger = new ErrorLogger();
void CreatePost(Database db, string postMessage)
{
try
{
db.Add(postMessage);
}
catch (Exception ex)
{
errorLogger.log(ex.ToString())
}
}
}

11. LOOKS GOOD!?

12. OPEN/CLOSED PRINCIPLE
Software entities (classes, modules, functions, etc.) should be
open for extensions, but closed for modification.

13. CODE SAMPLE

14. LISKOV SUBSTITUTION
PRINCIPLE
If S is a subtype of T, then objects of type T may be replaced
(or substituted) with objects of type S

15. CLIENT DOES NOT NEEDTO
KNOW SPECIFICS

16. LOOKS ABOUT RIGHT…

17. INTERFACE SEGREGATION
PRINCIPLE
The interface segregation principle states that no client should
be forced to depend on methods it does not use.

19. DEPENDENCY INVERSION
PRINCIPLE
High-level modules should not depend on low-level modules. Both should depend on
abstractions.
Abstractions should not depend on details. Details should depend on abstractions

20. COMPILETIME DEPENDENCY

21. COMPILETIME DEPENDENCY

22. COMPILETIME DEPENDENCY

23. CODE SAMPLE

24. HEXAGONAL, ONION,
CLEAN…
source: https://herbertograca.com/2017/11/16/explicit-architecture-01-ddd-hexagonal-onion-clean-cqrs-how-i-put-it-all-together/

25. SOURCES
• https://www.youtube.com/watch?
v=QHnLmvDxGTY
• https://www.youtube.com/watch?
v=BHnMItX2hEQ
• https://itnext.io/solid-principles-explanation-and-
examples-715b975dcad4

26. GOOD READS

27. QUESTIONS!?