A domain driven approach to Kotlin's new types

A short roundup of two new class types introduced in Kotlin, and how our programs can use them to improve maintainability.

Final code snippet: https://gist.github.com/pakoito/0b942c6f68441b76756a7a761cb9272d

Talk summary: https://skillsmatter.com/meetups/8409-lscc-talks-september-2016

Transcript

1. A DOMAIN DRIVEN APPROACH TO KOTLIN'S NEW TYPES PACO ESTEVEZ
2. FROM CLASSES TO TYPES EAT YOUR VEGGIES
3. CLASSES ENCAPSULATE DATA AND BEHAVIOUR. Classic OOP
4. DATA
5. DATA PROBLEMS ▸ Beans and not Beans ▸ Immutability ▸ Nullables and validation ▸ equals(), hashCode(), and toString()
6. DATA CLASSES IN KOTLIN ▸ Synthetic accessors ▸ val for immutable, var for mutable ▸ Nullable types and Default values ▸ data qualifier: all of the above plus equals(), hashCode() and toString()
7. BEHAVIOUR
8. HERE BE MONSTERS BEHAVIOUR IN JAVA
9. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour
10. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour ▸ Express execution flows as data
11. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour ▸ Express execution flows as data ▸ Encode behaviour in types
12. DOMAIN DRIVEN DESIGN WITH TYPES ▸ Separate data from behaviour ▸ Express execution flows as data ▸ Encode behaviour in types ▸ Make illegal states unrepresentable
13. 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
14. SEALED CLASSES BEHAVIOUR IN KOTLIN
15. SEALED CLASSES IN KOTLIN ▸ Closed inheritance ▸ Requires dereferencing using when() -> is ▸ Data classes and implement interfaces (1.1) ▸ Type alias (1.1)
16. 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