Koin vs Dagger (Service Locator vs D.I.)

With Koin 2.0 it’s time for us to evaluate this age old debate. What exactly do we mean by service locator vs dependency injection? Does it matter in a modern age? I will discuss this topic along with how both libraries are implemented with an emphasis on their differences and how that affects us.

1. service locator (koin) vs dependency injection (dagger) brian plummer @plummermakes
2. Why this talk
3. Koin 2.0 - May 2019
4. Looks really neat!
5. and it got me thinking!
6. We have lots of options today
7. What do you use?
8. Let’s take some steps back
9. Inversion of Control • Swappable Components • Decoupling or modularity • E.g. Logger implementations
10. –Michael Mattsson 1996 “This inversion of control is sometimes named the Hollywood principle, “Do not call us, we call You””
11. Martin Fowler
12. Martin Fowler • Popularized the term Dependency Injection • A signing member of the Manifesto for Agile Software Development • Inversion of Control Containers and the Dependency Injection pattern • Strangler Fig Pattern
13. Dependency injection is a technique whereby one object supplies the dependencies of another object
14. DI implements IoC through composition
15. No Injection
16. Why is no injection bad? • No Inversion of Control • Can’t mock out our data source
17. 3 Types of Injection • Constructor • Setter • Interface
18. Constructor Injection
19. Constructor Injection shows us bad smell
20. Setter Injection
21. Interface Injection
22. how dagger works • Compile time verification of dependencies • Compile time code generation
24. Service Locators
25. The service locator pattern is used to encapsulate the processes involved in obtaining a service with a strong abstraction layer
26. Static Service Locator
27. Dynamic Service Locator
28. how koin works
29. Conclusions on DI vs SL • Both provide separation • Difference is how dependencies are provided • Not mutually exclusive
30. Not mutually exclusive? • Dependencies created with injection -> served up via service locator • Can create dependencies with constructor injection
31. Thoughts…
32. Thoughts - Guarantees • What guarantees do we have? • Hard guarantees or pinky swears?
33. Thoughts - Costs • What are the costs? • Increased complexity? • Increased build time?
34. Thoughts - You! • What is your situation? • Greenfield vs Existing • Onboarding of new developers
35. What does it give us? • Abstracts how we construct our dependencies • Improves testability • Scoping
36. –Martin Fowler “The choice between Service Locator and Dependency Injection is less important than the principle of separating service configuration from the use of services within an application.”
37. Thank you! @plummermakes