> "The actual implementation of Universalis uses Kotlin DataFrames"

Neat. My favorite talk at the 2025 Kotlin Conf was the demo of the new compiler plugin that allows ad-hoc type inference from DataFrame expressions.

Essentially, say that you have an input type like:

  type User { name: String, age: Int }

And you do something like ".map(it => { doubledAge: it.age * 2 })"

The inferred type of that intermediate operation is now:

  type User_synthetic { doubledAge: Int }

Which is wild, since you essentially have TypeScript-like inference in a JVM language.

Timestamp to talk:

https://www.youtube.com/watch?v=F5NaqGF9oT4&t=543s