Pragmatic Kotlin Libraries: Containing Platform Types

In this talk I present a pragmatic approach for porting Java Libraries to Kotlin without leaking platform types into the public API through a interesting case study.

Platform types destroy some of the wonderful safety guarantees that Kotlin provides. They're a necessary evil to provide nice interop with Java, but that doesn't mean we have to allow them to propogate throughout our code base.

The example we'll look at is creating a Kotlin version of the wonderful Github Scientist library. Recently, I was trying to PoC something out for a team to illustrate how Github Scientist's interesting approach to data-driven refactoring could be applied in Kotlin. Unfortunately, there wasn't a Kotlin version of Github Scientist available, so I had to create one :).

Transcript

1. Welcome to Chicago Kotlin!
2. Pragmatic Kotlin Libraries - David Julia Associate Director of Engineering @Pivotal Software Twitter: @DavidJulia
3. The Problem • We have legacy code calculating an estimated price for a good • The old way is slow! • We have a new faster way of calculating those prices, but we’re not sure if we’ve covered all of the edge cases
4. Github Scientist “A Ruby library for carefully refactoring critical paths” The Solution
5. Github Scientist “A Ruby library for carefully refactoring critical paths” The Solution
6. Github Scientist Example require "scientist" class MyWidget def allows?(user) experiment = Scientist::Default.new "widget-permissions" experiment.use { model.check_user?(user).valid? } # old way experiment.try { user.can?(:read, model) } # new way experiment.run end end
7. Github Scientist Example: An Even Nicer Version! require "scientist" class MyWidget include Scientist def allows?(user) science "widget-permissions" do |experiment| experiment.use { model.check_user(user).valid? } # old way experiment.try { user.can?(:read, model) } # new way end # returns the control value end end
8. How do we get this on the JVM?
9. Options • Will it work in jRuby? • Find a Java implementation and use it • Implement your own? • Wrap a Java Library
10. Options • Will it work in jRuby? <- Could be awful • Find a Java implementation and use it <- I miss Kotlin • Implement your own? <- I started down this path • Wrap a Java Library <- This is where I landed
11. Wrapping Java Libraries = A Pragmatic Approach! • Don’t pollute your code with platform types • Leverage nice clean Kotlin!
12. And now, some code. https://github.com/dajulia3/kotlin-scientist-meetup