Functional core, imperative shell

Clean Architecture and Gary Bernhardt's functional core, imperative shell. They are all the same. This presentation will simplify and clarify an architecture that so many people have "discovered" independently. It is an architecture that decouples an application's core logic from the services it uses. It allows an application to be equally driven by users, programs, automated tests or batch scripts.

Transcript

1. Functional Core Imperative Shell
2. Pains Lack of reuse Complexity Decrease in delivery velocity Maintenance difficulty
3. It doesn’t have to be this way
4. Architecture Goals A place for everything Testable Technology agnostic consumption Maintainable
5. Historical Solutions Transaction script Layers
6. Transaction Script
7. Good Bad Simple! Easy debugging …? No reuse No abstraction Algorithm hidden Refactoring difficult
8. Badwords 1. Query a web page 2. Search for “bad words” 3. Rate the page on the number of bad words 4. Report the number of bad words to level up 5. Write the url to a text file, if the # of bad words is odd
9. Transaction Script Demo
10. Layers
11. Good Bad Some reuse Hard to test Full stack coupling Inflexible
12. Hexagonal Architecture
15. Functional Core Imperative Shell Algorithms & coordinators Shell Core UI Database Service
16. Keep logic and I/O separate Implement application logic in a pure functional core The core should have no external dependencies Define an application API (ports) to be used by all presentations (adapters) All dependencies point inwards towards the core Rules
18. IoC and Mocking 1. Query that does not depend on an output of the computation 2. Query that does depend on the an output of the computation 3. Output
19. Badwords 1. Query a web page 2. Search for “bad words” 3. Rate the page on the number of bad words 4. Report the number of bad words to level up 5. Write the url to a text file, if the # of bad words is odd
20. Activity Home Fetching a URL from the terminal Core Shell Fetching content of a web page Find ‘bad words’ in content Calculate rating
21. Activity Home Write file? Core Shell Write file
22. Functional Core Imperative Shell Demo
23. Testing Goals Verify the logic Don’t test the framework
24. Test Demo
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