KMPStateSupportMacro

#KMPStateSupport is a Swift macro that generates withChanges(...) and apply(path:value:) functions for a Kotlin Multiplatform (KMP) state type, routing AnyKeyPath-based property updates through KTStateWrapper key paths.

Requirements

• Swift 6.3 toolchain or later (tested with Xcode 27)
• Platforms: macOS 14, iOS 13, tvOS 13, watchOS 6, macCatalyst 13

Installation

Add this package to your SwiftPM dependencies and import KMPStateSupportMacro in the files where you use the macro.

Usage

Use #KMPStateSupport inside an extension on your KMP state type. Pass the state type first, followed by one ("propertyName", Type.self) tuple per property:

import KMPStateSupportMacro

extension ProfileState {
  #KMPStateSupport(
    ProfileState.self,
    ("name", String.self),
    ("count", Int.self)
  )
}

Generated:

public func withChanges(name: String? = nil, count: Int? = nil) -> Self {
  Self(name: name ?? self.name, count: count ?? self.count)
}

public func apply(path: AnyKeyPath, value: Any) -> Self {
  typealias State = ProfileState

  return switch path {
  case \KTStateWrapper<State>.kt.name:
    withChanges(name: value as? String)
  case \KTStateWrapper<State>.kt.count:
    withChanges(count: value as? Int)
  default:
    fatalError("Unknown key path \(path)")
  }
}

Optional Properties

Optional properties (for example ("trigger", Trigger?.self)) become closure parameters of type (() -> T?)? = nil, so a value can be explicitly reset to nil.

Kotlin Bridged Types

Kotlin boxed types such as KotlinDouble, KotlinInt, or KotlinBoolean are exposed with their Swift equivalents (Double, Int32, Bool, ...) in withChanges(...) and apply(path:value:), and converted back to the Kotlin type when building the new state.

Access Level

The generated functions are public by default. Pass internalAccessor: true as the last argument to generate them with internal access:

#KMPStateSupport(ProfileState.self, ("name", String.self), internalAccessor: true)