Kotlin External Function

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Syntax

external fun computeHash(input: String): ByteArray

class NativeProcessor {
    // Member external function
    external fun processData(buffer: ByteArray): Int
}

// Extension external function
external fun String.toNativeString(): Long

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Technical Characteristics

• No Body: An external function cannot have a block body { ... } or an expression body = .... Attempting to provide one results in a compilation error.
• Property Accessors: The external modifier can be applied to property getters and setters. To target an accessor, the external modifier must be placed directly on the get or set keyword itself, rather than on the property declaration.

val systemTime: Long
    external get
    
var hardwareState: Int
    external get
    external set

• Visibility and Modifiers: external functions support standard visibility modifiers (private, internal, public) and can be combined with other modifiers like open or override when participating in inheritance hierarchies.

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Platform-Specific Resolution

class NativeProcessor {
    init {
        System.loadLibrary("processor_lib")
    }
    external fun processData(buffer: ByteArray): Int
}

@JsModule("crypto-js")
@JsNonModule
external fun md5(message: String): String