73 lines
2.2 KiB
Markdown
73 lines
2.2 KiB
Markdown
# Kotlin Bridge: Lyng-First Class Binding
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This note describes the Lyng-first workflow where a class is declared in Lyng and Kotlin provides extern implementations.
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## Overview
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- Lyng code declares a class and marks members as `extern`.
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- Kotlin binds implementations with `LyngClassBridge.bind(...)`.
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- Binding must happen **before the first instance is created**.
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- `bind(className, module, importManager)` requires `module` to resolve class names; use
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`bind(moduleScope, className, ...)` or `bind(ObjClass, ...)` if you already have a scope/class.
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- Kotlin can store two opaque payloads:
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- `instance.data` (per instance)
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- `classData` (per class)
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## Lyng: declare extern members
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```lyng
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class Foo {
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extern fun add(a: Int, b: Int): Int
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extern val status: String
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extern var count: Int
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private extern fun secret(): Int
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static extern fun ping(): Int
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fun callAdd() = add(2, 3)
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fun callSecret() = secret()
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fun bump() { count = count + 1 }
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}
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```
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## Kotlin: bind extern implementations
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```kotlin
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LyngClassBridge.bind(className = "Foo", module = "bridge.mod", importManager = im) {
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classData = "OK"
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init { _ ->
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data = CounterState(0)
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}
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addFun("add") { _, _, args ->
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val a = (args.list[0] as ObjInt).value
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val b = (args.list[1] as ObjInt).value
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ObjInt.of(a + b)
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}
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addVal("status") { _, _ -> ObjString(classData as String) }
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addVar(
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"count",
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get = { _, instance ->
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val st = (instance as ObjInstance).data as CounterState
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ObjInt.of(st.count)
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},
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set = { _, instance, value ->
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val st = (instance as ObjInstance).data as CounterState
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st.count = (value as ObjInt).value
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}
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)
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addFun("secret") { _, _, _ -> ObjInt.of(42) }
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addFun("ping") { _, _, _ -> ObjInt.of(7) }
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}
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```
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## Notes
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- Visibility is respected by usual Lyng access rules; private extern members can be used only within class code.
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- Use `init { scope -> ... }` for receiver-style init, or `initWithInstance { scope, instance -> ... }` for explicit instance access.
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- `classData` and `instance.data` are Kotlin-only payloads and do not appear in Lyng reflection.
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- Binding after the first instance of a class is created throws a `ScriptError`.
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