Kotlin "by" Delegation

Delegation is design pattern that allows same code reuse as inheritance. In this talk we go through the details of why we should favor composition over inheritance by using delegation pattern and how the Kotlin programming language implements this concept out of the box.

Transcript

1. Kotlin “by” Delegation G O O G L E D E V E L O P E R G R O U P D A K A R R y g e l L o u v
2. I am here because I know few stuff about programming. Hello! I Am Rygel Louv @rygelouv @rygellouv @rygel
3. Delegation?
4. —Google
5. “ “In software engineering, the delegation pattern is an object-oriented design pattern that allows object composition to achieve the same code reuse as inheritance.” —Wikipedia
6. Inheritance Seriously ? We all know what it is
7. Inheritance can be bad ?
8. Problems with Inheritance Breaks encapsulation Builds static relationship Multiple inheritance brings The Diamond problem Etc…
9. Favor Composition Over Inheritance
10. Composition ?
11. Kotlin “by” Class Delegation
12. Use case: Inheritance
13. Composition with Manual Delegation
14. Composition with Manual Delegation
15. Let’s Use Kotlin now
16. Composition with Kotlin Delegation
17. Rules Can only delegates Interface Must have a concrete class that implements the Interface class ClassName: ParentInterface by ObjectDelegate Syntax: Delegate to instance object of that concrete class
18. Composition with Kotlin Delegation
19. How does it work ?
20. Decompile
21. Kotlin “by” Property Delegation
22. “ “Put in one place a property behavior so that it can be reused”
23. Lazy Property “The value gets computed only upon first access”
24. Lazy Property Delegation val/var <property name>: <Type> by <expression> Syntax:
25. Lazy property delegation By default, the evaluation of lazy properties is synchronized: the value is computed only in one thread, and all threads will see the same value.
26. Observable Property “Listeners get notified about changes to this property”
27. Observable Property Delegation
28. Custom Delegate “Create your own delegates”
29. Custom Property Delegation
31. Thanks! Any questions? @rygelouv @rygellouv @rygel