Native payload types

Structs, enums, Date and Data across the Swift and Kotlin boundary

Method arguments, results, view props and callback arguments cross as JSON by default, and four richer shapes cross with it: a Codable struct or data class crosses as its object shape, a String or Int backed enum crosses as its raw value, a Date crosses as an ISO string revived to a Date, and Data or ByteArray crosses as base64 revived to a Uint8Array.

struct Point: Codable {
  var x: Double
  var y: Double
  var label: String? = nil
}

enum Direction: String {
  case north
  case south
}

@MainActor final class Atlas: PeachModule {
  init() {}

  func pin(_ point: Point) -> Point { point }
  func heading(_ direction: Direction) -> Direction { direction }
  func at(_ when: Date) -> Date { when }
}

data class Point(val x: Double, val y: Double, val label: String? = null)

enum class Direction {
    NORTH,
    SOUTH
}

object Atlas : OneModule {
    fun pin(point: Point): Point = point
    fun at(when: Date): Date = when
    fun blob(data: ByteArray): ByteArray = data
}

import { Atlas, type Point } from './native/Atlas.swift'

const point: Point = { x: 1, y: 2 }
await Atlas.pin(point)
await Atlas.at(new Date())

A struct field with a value is optional in TypeScript; Codable and the generated Kotlin glue fill the default when the key is missing. A Kotlin default must be visible to the generated glue. Structs nest, including inside arrays and maps. An enum needs its cases listed without explicit raw values or associated values. Every struct and enum lives in the file that uses it, must be visible to the generated glue, and a Swift struct must conform to Codable in its declaration. Anything else keeps failing with the file and line that declares it.

Pass a real Date and a real Uint8Array: anything else throws before the call leaves JavaScript. Native results revive the same way, so what arrives is a Date and a Uint8Array, never the string on the wire.