Initialize variables with ".()" expression in Kotlin-CodePudding

I'm using Ktor to make websocket requests.
The method "websocket(...)" I use takes two lambda expressions.

So as I only can call one with curly brackets I have to give the other one via a variable. So I tried this:

val request: HttpRequestBuilder.() -> Unit
val socket = ktorHttpClient.webSocket(request = request) {

}

The data types fit now but of course it still says "Variable 'request' must be initialized", so I tried to initialize it:

val request: HttpRequestBuilder.() -> Unit = HttpRequestBuilder.()

Now the error is gone but inside the last brackets it says "Expecting an expression", what am I missing here?

PS: Maybe there's even somebody who can explain in detail how initialization works when using ".()".

CodePudding user response：

As you said yourself, you need to pass two lambdas. You can do it either directly:

ktorHttpClient.webSocket({ /* request lambda */ }) {
    /* block lambda */
}

Or split it as you did:

val request: HttpRequestBuilder.() -> Unit = { /* request lambda */ } 
val socket = ktorHttpClient.webSocket(request) {
    /* block lambda */
}

More info on how to initialize lambdas / function types can be found here: https://kotlinlang.org/docs/lambdas.html#instantiating-a-function-type