KMP&CMP Community Boosts ArkTS-Kotlin Interop with Advanced Syntax & Compile-Time Type Solidification

In KMP (Kotlin Multiplatform) development for HarmonyOS, cross-language interaction between ArkTS and Kotlin is a core scenario. ArkTS has accumulated native base capabilities that KMP must call to avoid duplicate development, while ArkTS business code needs to invoke KMP-encapsulated cross-platform capabilities (network requests, data parsing) to ensure multi-platform logic consistency.

However, the native NAPI interaction chain is verbose: developers must sequentially load modules, obtain objects, extract methods, convert parameters, and invoke methods. The KMP community edition aims to provide a better cross-language development experience and performance. Kuaishou, as a community member, actively contributes to syntax expansion and annotation enhancement.

Syntax Completeness Improvement: 28% → 78%

The cross-language library now supports additional high-level Kotlin syntax:

Complex generics — e.g.,

@KNExportFunction fun <T : BaseViewModel> consumeElement(element: GenericElement<in T, *>)

Function expressions — return type as lambda callable from ArkTS:

@KNExportFunction fun returnKtBlock(a: Int, b: Int): (Int) -> String { return { c: Int -> val sum = a + b + c; "$sum" } }

; parameter type as lambda invokable from ArkTS:

@KNExportFunction fun invokeTsBlock(cb: (arg: Int) -> String): String { return cb(1) }

Abstract class inheritance — exported abstract classes can be subclassed in ArkTS:

@KNExportClass abstract class AbstracClassTest(val x: Int, val y: Int) { abstract fun caclate(): Double; fun sum(): Int = x + y }

typealias —

@KNExportTypeAlias typealias myLambda = (Int, (Int?) -> String?) -> String?

These extensions improve cross-language development convenience and enable the library to adapt to more real-world business code scenarios.

Annotation Capability Enhancement: Compile-Time Type Solidification

Manual low-level conversion logic is time-consuming and error-prone. Declarative annotations shift complex conversion logic to auto-generated bridge code. For example, adding @KNExportFunction to a Kotlin function enables direct invocation from ArkTS.

This contribution introduces Kuaishou's KSP (Kotlin Symbol Processing) bridge code generation capability, achieving compile-time type solidification. Two new annotations were added: @KNExportTypeAlias — supports exporting typealias definitions @KNHide — hides specific declarations from cross-language exposure

Traditional cross-language interaction suffers from generic erasure at runtime. This work solidifies Kotlin-side types at compile time so runtime carries complete type information. The core technical pipeline:

KSP (sole type window) — captures full KSType at compile time; generic parameters, nullability, and nested structures propagate layer by layer.

typeOf<T> (type information solidification) — writes KType into machine code, bypassing generic erasure, serving as the compile-time to runtime type bridge.

KNapiInvokable (runtime carrier) — TypeConverter dispatches precisely based on classifier and recursively restores generic parameters without reflection.

The article includes a link to the cross-language library usage guide:

https://atomgit.com/CPF-KMP-CMP/docs/blob/main/zh-cn/深入开发/跨语言调用用户手册.md