Building DSLs in Kotlin for Fun and Profit

Talk given at Milan Kotlin Community Conference.
Talk includes a demo, the sample can be found here: https://github.com/zmarkan/kurl

Transcript

1. @zmarkan @pusher Building 
 DSLs in Kotlin 
 for fun and profit
2. @zmarkan @pusher Pusher Hosted APIs for 
 collaboration & communication Channels, Beams, Chatkit pusher.com @pusher
3. @zmarkan @pusher DSLWTF
4. @zmarkan @pusher •Adapting the language to suit a domain •Allowing non-devs to read code •Making the API neater DSLs are for
5. @zmarkan @pusher + Save time on repetitive things + Improve readability - Learning curve & maintainability of DSL - (Can cause) unintended side-effects
6. @zmarkan @pusher •Adapting the language to suit a domain •Allowing non-devs to read code •Making the API neater •Job security DSLs are for
7. @zmarkan @pusher Use-Cases
8. @zmarkan @pusher Internal DSLs live inside the host language External have fewer boundaries Depends on your “domain” Internal vs External DSLs
9. @zmarkan @pusher • Text processing - awk/sed • Testing - gherkin / hamcrest / *spec • Configuration - make, rake, gradle • Visual, statistic, etc…
10. @zmarkan @pusher • View creation - Anko / hotlinx.html • Build definition - gradle.kts • Injection - Koin • …
11. @zmarkan @pusher • Type-safe Builders • Configuration syntax • Tasks, objects, …
12. @zmarkan @pusher What Kotlin Gives us
13. @zmarkan @pusher • Type aliases • Extension functions • Lambdas • named arguments • default values
14. @zmarkan @pusher • Function Literals with receiver • Infix functions • Operator overloading • @DslMarker annotation
15. @zmarkan @pusher Instantiate function types with literals Receiver itself providing the receiver object Common way to “enter” the DSL Literals with receiver
16. @zmarkan @pusher Literals with receiver
17. @zmarkan @pusher Call methods without the . and ()
 object.method(argument) becomes
 object method argument. Infix notation
18. @zmarkan @pusher Infix notation
19. @zmarkan @pusher Override +, -, /, (), and others to add arithmetic-like methods to classes Operator overloading
20. @zmarkan @pusher Operator overloading
21. @zmarkan @pusher Override +, -, /, (), and others to add arithmetic-like methods to classes …or with arithmetic ones, if you like to watch the world burn Operator overloading
22. @zmarkan @pusher Never EVER do that.
24. @zmarkan @pusher •Avoid children from accessing methods on the parent receiver •Limit scope for what can be called •Compiler will enforce it @DslMarker
25. @zmarkan @pusher Demo - kurl
 Kotlin HTTP DSL
26. @zmarkan @pusher •Kotlin gives you tools for building DSLs •DSLs can make APIs more readable •Configuration, testing are the top use-cases •Avoid anything “too” crazy Summary
27. @zmarkan @pusher COM IN G (VERY) SOON
28. @zmarkan @pusher Zan Markan zan@pusher.com / pusher.com slides: bit.ly/building-kotlin-dsls sample: https://github.com/zmarkan/kurl fin
29. @zmarkan @pusher • https://kotlinlang.org/docs/reference/type-safe-builders.html • https://github.com/zsmb13/VillageDSL • https://speakerdeck.com/writtmeyer/kotlin-dsls • https://javieracero.com/blog/internal-vs-external-dsl • https://martinfowler.com/bliki/InternalDslStyle.html Resources