Hello everyone, I have just started using Kotlin at work. Can someone explain what this line of code...

# getting-started

[Sajal]

Hello everyone, I have just started using Kotlin at work. Can someone explain what this line of code mean (declaring a method argument):

interface Contract

fun someMethod(someLambda: Contract.() -> Unit) {

}

Here we are declaring a method that takes a lambda someLambda , where the lambda must take in a Contract.() and return nothing (Unit). But what does Contract.() mean? Are we dot-accessing something on an interface?

[ephemient]

https://kotlinlang.org/docs/lambdas.html#function-types

Function types can optionally have an additional receiver type, which is specified before the dot in the notation

[Sajal]

I was looking for a name of this syntax to read up on it. Thanks.

[Tung97 Hl]

someLambda is the parameter with the type of function: Contract.() mean the someLambda must be an extension function of type Contract, and someLambda is the function which returns Unit.

[ephemient]

not quite. it doesn't need to be an extension function:

val someLambda: (Contract) -> Unit = { ... }
someMethod(someLambda)

will compile and run just fine. what it does do, though, is make it so that when you write a lambda right there, it is inferred to have a receiver of type `Contract`:

someMethod {
    this is Contract
}

[Tung97 Hl]

@ephemient thanks for correct me