ShouldRefineInSwift.md

Interop annotations - @ShouldRefineInSwift

@ShouldRefineInSwift helps to replace a Kotlin declaration with a wrapper written in Swift. Experimental.

Explanations

In Kotlin:

interface Person {
    @ShouldRefineInSwift
    val namePair: Pair<String, String>
}

class RealPerson: Person {
    override val namePair = "First" to "Last"
}

In Swift:

extension Person {
    var name: (firstName: String, lastName: String) {
        let namePair = __namePair
        return (namePair.first! as String, namePair.second! as String) 
    }
}

func shouldRefineInSwiftExample(){
    let authorNames = RealPerson().name
    print("Author is: \(authorNames.firstName) \(authorNames.lastName)")
}

Using the @ShouldRefineInSwift annotation, we are indicating that we intend to refine the definition of namePair in Swift. The annotation marks the property as swift_private in the generated Objective-C API. Such declarations get a __ prefix, which makes them invisible from Xcode’s autocomplete.

Setup

Since the annotation is experimental, it is necessary to opt-in.

sourceSets {
    all {
        languageSettings.optIn("kotlin.experimental.ExperimentalObjCRefinement")
    }
}

Credits

With thanks to Rick Clephas for the annotation contribution and example code.

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