Reprise: The four design smells (Rigidity, Fragility, Immobility, Viscosity) SOLID reprise: Quick overview of the first five principles SRP Update: It's not just about classes! Package Cohesion Principles: * Release-Reuse Equivalency Principle (REP) * Common Closure / Cohesion Collocation Principle (CCP) * Common Reuse Principle (CRP) Package Coupling Principles: * Acyclic Dependencies Principle (ADP) * Stable Dependencies Principle (SDP) * Stable Abstractions Principle (SAP) Mnemonics for remembering them: ACCESS, CASE And don't forget Robert "Uncle Bob" C. Martin! This is the original Google Drive slides: https://docs.google.com/a/nelkinda.com/presentation/d/1yEOCYWhIgMfiDAJYtvB5ongE2qvcA91tPqLB4TzEcwM/edit?usp=sharing

1. Beyond SOLID:
The Package Principles
Red Panda Innovation Labs
Code Words 2016-04-22
Christian Hujer
CEO / CTO Nelkinda Software Craft Pvt Ltd

2. Agenda
1.The Four Design Smells
2.Origins and Reprise of SOLID
3.ACCESS / CASE - The Package Principles
a.Package Cohesion Principles
b.Package Coupling Principles
c.Mnemonics

3. Definitions
Software Entity
Statement / line / method / class / package / service
Component
Logical (model / architecture / design) group of Software Entities
Package
Physical (e.g. directory, gem, jar) group of Software Entities
Collocation
Putting things in the same Component / Package
Cohesion
Things that are changed together
Coupling
Dependency that potentially propagates change

4. 1.
The Four Design Smells

5. The Four Design Smells
●Rigidity
●Fragility
●Immobility
●Viscosity

6. Rigidity
What is Rigidity?
Existing Code that causes Effort (known Effort)
What causes Rigidity?
Coupling

7. Fragility
●What is Fragility?
○Existing Code that causes Risk (unknown Effort)
●What causes Fragility?
○Coupling
○Lack of Cohesion

8. Immobility
What is Immobility?
The difficulty (extra Effort) to reuse something.
Rigidity and Fragility in the context of reuse.
What causes Immobility?
Coupling
Lack of Cohesion

9. Viscosity
What is Viscosity?
Continuous extra Effort (Time)
What causes Viscosity?
Coupling
Bad development setup / tools

10. 2.
The SOLID Principles
A short reminder

11. SRP - Single Responsibility
OCP - Open-Closed
LSP - Liskov Substitution
ISP - Interface Segregation
DIP - Dependency Inversion
Reminder of SOLID

12. Design Principles and Design
Patterns (2000)
Mentions 10 principles
● Principles of Object Oriented Class Design:
OCP, LSP, DIP, ISP
● Principles of Package Architecture:
REP, CCP, CRP, ADP, SDP, SAP
Origin of SOLID

13. 3.
The Package Principles

14. The Package Principles
Package Cohesion Principles
REP - Release Reuse Equivalency
CCP - Common Closure
CRP - Common Reuse
Package Coupling Principles
ADP - Acyclic Dependencies
SDP - Stable Dependencies
SAP - Stable Abstractions

15. 3.a.
Package Cohesion
Principles

16. Release Reuse Equivalency Principle
“The granule of reuse is the granule of release.”
Reuse === Release
Bundler / Gems, NPM, Jars / Maven, RPM,
APT, Brew...

17. Common Closure Principle (Cohesion)
“Classes that change together belong
together.”
⇒ This also is a nice pragmatic definition of
cohesion and that cohesive elements should be
collocated.
I call it: Cohesion Collocation Principle

18. Common Reuse Principle (Cohesion)
“Classes that aren’t reused together should not
be grouped together.”
This is really the inversion of the idea that
“Classes that change together belong
together.”

19. 3.b.
Package Coupling
Principles

20. Acyclic Dependencies Principle
“The dependencies between packages must
not form cycles.”

21. Stable Dependencies Principle
“Depend in the direction of stability.”

22. Stable Abstractions Principle
“Stable packages should be abstract
packages.”

23. 3.c.
Mnemonics
How to remember all this stuff?!

24. ACCESS
Your new mnemonic acronym
Combine to SOLID ACCESS

25. ACCESS Mnemonic Acronym
ADP - Acyclic Dependencies
CCP - Common Closure (Cohesion Collocation)
CRP - Common Reuse
REP - Release Reuse Equivalency
SAP - Stable Abstractions
SDP - Stable Dependencies

26. CASE
A shorter mnemonic acronym
Combine to SOLID CASE

27. CASE - A new mnemonic acronym
Cohesion / Common
CCP / CRP Common Closure / Reuse
Acyclic
ADP Acyclic Dependencies
Stability
SAP / SDP Stable Abstractions / Dependencies
Equivalence
REP Release Reuse Equivalency

28. Related Topics
Software Architecture and Design
Software Metrics
Clean Code
Refactoring
TDD, ATDD and BDD
Agile Methods, Scrum, Extreme Programming
Continuous Integration / Delivery / Deployment, DevOps
Software Craftsmanship
Law of Demeter / Tell Don’t Ask
CQS - Command Query Separation
Programming Paradigms (Functional, Structured, Object-Oriented, Object-
Functional, Logic)

29. References
● SOLID and Package Principles, Design Smells: Design
Principles and Design Patterns (Robert C. Martin, 2000)
● ACCESS mnemonic: Christian Hujer
● CASE mnemonic: Christian Hujer and Mark Burns

30. Thank you!
Questions?
Follow me on Twitter:
@christianhujer