Poko goes multiplatform

August 9, 2023

Poko is a Kotlin compiler plugin that generates equals, hashCode, and toString functions for annotated classes based on their properties. Inspired by Jake Wharton’s blog post on maintaining compatibility in public APIs , it partially mimics the behavior of Kotlin data classes while leaving out the copy and componentN functions, which are difficult to maintain without breaking API compatibility. Our Paraphrase and Redwood runtimes use Poko.

The equals, hashCode, and toString functions are familiar to all JVM developers. But Kotlin generates the exact same set of functions for data classes on all of its multiplatform targets—not just the JVM. It stands to reason that Poko should do the same. And thanks to a slew of recent contributions from Jake, now it does! In addition to the JVM and Android platforms it has supported since its first release 3 years ago, Poko 0.15.0 now supports native and JS targets as well.

The generated functions behave the same on all platforms, and by default implement the same behavior that data classes implement: equals and hashCode depend on each of the class’s primary constructor properties, and toString prints the values of each of these properties.

In addition to standard data class behavior, Poko also recently added support for respecting array content via an @ArrayContentBased annotation. Normally, data classes and Poko classes compare array properties only by reference (unlike collections, which always compare contents), because this mirrors the JVM’s default treatment of arrays. But in some cases, the performance gains of using arrays are considerable—particularly on JS, where List types involve several wrappers around the native Array. In runtimes like those of Paraphrase and Redwood, which are only invoked by generated code, the awkwardness of using array properties is less important than this performance difference. @ArrayContentBased makes it possible to opt in to array use in these cases. Like the rest of Poko, it now works for all target platforms.

Whether using arrays or not, it’s important for library authors to maintain API compatibility across releases. Now, Kotlin multiplatform library authors can easily ship public data models with minimal concern about breaking their APIs.

This post concludes Cash App’s Summer of Kotlin Multiplatform series.

How Poko works