Generic functions.md

Generic functions

Automatic type inference and nullability are not supported.

Explanations

Let's write a simple generic function that takes generic as input and returns the same.

fun <T> convert(data: T): T {  
    return data  
}

private fun example() {
    val s: String = convert("322")
    val p: Int = convert(122)
    val l: Long = convert(122L)
}

On the Swift side, the type T is interpreted as Any?, which means that additional type casts have to be introduced:

let result1: Int = GenericFunctionsKt.convert(data: 12) as! Int
let result2: String = GenericFunctionsKt.convert(data: "'222'") as! String

In order for Swift to see that the type is definitely not null, you need to use the boundary syntax on the Kotlin side:

fun <T : Any> strictedGeneric(data: T): T {  
    return data  
}

Then the function strictedGeneric on the Swift side returns Any, not Any?.

But automatic type inference is not supported.

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