Revisiting types in Kotlin

Snippets
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Collections and functions:
https://gist.github.com/pakoito/0fd5d1bd6c1523ad965b52cc7b592433

Domain Modeling with Sealed classes:
https://gist.github.com/pakoito/0b942c6f68441b76756a7a761cb9272d

VIDEO
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TBD

Transcript

1. REVISITING TYPES IN KOTLIN “PACO” ESTEVEZ
2. FROM CLASSES TO TYPES EAT YOUR VEGGIES
3. CLASSES ENCAPSULATE DATA AND BEHAVIOUR. Classic OOP
4. DATA
5. DATA CHALLENGES ▸ Beans and not Beans ▸ Immutability ▸ Nullables and validation ▸ equals(), hashCode(), and toString()
6. BEHAVIOUR
7. HERE BE MONSTERS BEHAVIOUR IN JAVA
8. BUT WHAT IS A TYPE ANYWAY? Someone at the back
9. WHAT IS A TYPE ▸ A finite set of encapsulated operations ▸ A representation of either value or behaviour ▸ Some types can be represented with classes, some need language support ▸ They can be checked at compile time, so sometimes they’re called proofs ▸ Remember this
10. PRIMITIVES No implicit type coercion. Boxing is hidden from you.
11. FUNCTIONS
12. FUNCTIONS IN KOTLIN ▸ Functions are runtime objects too! ▸ Create an instance using operator :: ▸ Define them using lambda nomenclature ▸ A function as last parameter to another function gets syntactic sugar ▸ Great for DSLs
13. COLLECTIONS AND COMBINATORS
14. COLLECTIONS IN KOTLIN ▸ Saner version of Java’s, and fully compatible ▸ Two flavours: mutable and immutable ▸ Operations with function parameters: map, filter, reduce… https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/
16. DATA CLASSES
17. DATA CLASSES IN KOTLIN ▸ Synthetic accessors ▸ val for immutable, var for mutable ▸ Nullable types and Default values ▸ Named parameters ▸ data qualifier: all of the above plus equals(), hashCode() and toString()
18. OPEN CLASSES AND INTERFACES
19. HERE BE JAVA
20. ENUMS
21. ENUM CLASSES IN KOTLIN ▸ Similar to Java ▸ values ▸ ordinal position ▸ Implement Enum<T> interface if you’re a generic abstractions kind of person ▸ Look into Kotlin’s reified generics when you get home
22. SEALED CLASSES
23. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour
24. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour ▸ Express execution flows as data
25. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour ▸ Express execution flows as data ▸ Encode behaviour in types
26. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour ▸ Express execution flows as data ▸ Encode behaviour in types ▸ Make illegal states unrepresentable
27. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour ▸ Express execution flows as data ▸ Encode behaviour in types ▸ Make illegal states unrepresentable ▸ Push validation to edges
28. PART TWO
29. SEALED CLASSES IN KOTLIN ▸ Closed inheritance ▸ Accessing fields and methods requires dereferencing using when() and is -> ▸ The compiler checks that all cases are handled! ▸ Data classes and implement interfaces (1.1) ▸ Type alias (1.1)
30. MAKE THE COMPILER WORK FOR YOU! Me
31. WHAT IF I CAN’T USE KOTLIN? JAVA 8 ▸ JavaSealedUnions JAVA 6 ▸ RxSealedUnions SCALA ▸ You should be on stage pacoworks.com/ @fe_hudl github.com/pakoito tinyurl.com/KMobi16