For example, here we’ve got a function that accepts a List and returns Any. Alternatives Abstract Arguments and/or Return TypesĪn alternative to our generic function above would be a function that accepts a more abstract type. This shouldn’t trip you up much, since the real difference is that, in Kotlin, the return type has simply been moved to be after the function. In Java, the type parameter declaration goes before the return type. In Kotlin, the type parameter declaration goes before the function name. Generic functions in Kotlin are similar to Java, but the type parameter is declared in slightly different locations: fun middleItem(list: List): T = //. In other words, we didn’t have to cast the result back to an Int or String. (In fact, it can work with a List of any type!) When this function returns the result, the type is preserved. Val middleString: String = middleItem(listOf('one', 'two', 'three'))Īs this code demonstrates, our generic function can work with both List and List. Usage val middleInteger: Int = middleItem(listOf(1, 2, 3, 4, 5))

What exactly is the type of T? Well, it depends on the call sites, so let’s look at how we’d call this function. A return type of T, which is the same as the type of the items in the List.

An argument that accepts a List of items that are of type T.This type parameter declaration goes before the name of the function, and it’s written here as.

Here’s a Kotlin generic function that returns the middle-most item out of a List: fun middleItem(list: List): T = list Yeah, that’s a mouthful, so let’s just take a look at an example. Generic functions are functions that accept a type parameter, which allows different call sites to pass different types, without sacrificing type safety.

Kotlin any type