in Rust, I can define a `trait` (which roughly tra...

# getting-started

[y]

in Rust, I can define a trait (which roughly translated to a Kotlin interface), and then implement that trait for types which were defined elsewhere.

can I do something similar in Kotlin? I know I can kind of simulate this with extension functions.

[ephemient]

that wouldn't be compatible with the Java object model

[ephemient]

depending on what you're trying to do, you might be able to simulate it with extension functions, or possibly context receivers

[Youssef Shoaib [MOD]]

Context receivers are aboslutely the way to go here. Here's an example of how they can be used:

interface Summable<T> { // similar to a trait Summable that is implemented for some type T
    operator fun T.plus(other: T)
    val zero: T
}

// You can even define methods that need T to be summable
context(Summable<T>)
fun <T> List<T>.sumAll(): T = fold(zero) { acc, t -> t + acc }

// implementing Summable for a type is trivial
object IntSummable: Summable<Int> {
    override val zero = 0
    override fun Int.plus(other: Int) = this + other
}

//usage is slightly ugly in that you have to explicitly bring the implementation of Summable<Int> into scope

with(IntSummable) {
    listOf(1, 2, 3, 4, 5).sumAll()
}

[y]

that… looks quite good. thanks a lot. I’ll give it a try and see how it works for my use case.