Is there a simple way to create a generic type safe builder that can be used with a lambda like `functionName lt ClassName gt className functions ` I know it can be done specifically but I was wondering if there was a way to create a generic approach in Kotlin

I started with this ```interface BaseRobot fun lt T gt screen init T gt Unit T = init as T ```

with the limited context of having a generic way to call object members with a lambda `T gt R` is the correct approach but casting the lambda to `T` will never work at least the way you ve written it in your example

Is there a simple way to create a generic type safe builder kotlinlang #getting-started

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Title

Joshy Josh

12/04/2020, 11:19 PM

Is there a simple way to create a generic type-safe builder that can be used with a lambda? like

functionName<ClassName> { …className functions}

? I know it can be done specifically, but I was wondering if there was a way to create a generic approach. in Kotlin.

More specifically, where ClassName could be any class passed in the the type.

I started with this:

interface BaseRobot {
    fun <T> screen(init: T.() -> Unit): T = init as T
}

It allows to call, but then when using it will perform a cast error or do nothing with no error.

Shawn

12/05/2020, 12:36 AM

what exactly are you trying to accomplish with this?

Joshy Josh

12/05/2020, 12:38 AM

Basically have a generic way to call object members using a lambda notation,

screen<class> { function() }

Typically, when I create object for this I have to specify the class in the function using a function outside of the class utilizing the type safe builder approach.

Shawn

12/05/2020, 12:39 AM

I mean, if you have an instance of the object in question, you could use

run

with

, or

apply

Joshy Josh

12/05/2020, 12:40 AM

I did try, but got a casting error.

Shawn

12/05/2020, 12:40 AM

care to be be more specific about the error?

with the limited context of “having a generic way to call object members with a lambda”

T.() -> R

is the correct approach, but casting the lambda to

will never work (at least the way you’ve written it in your example)

Joshy Josh

12/05/2020, 12:44 AM

I stepped away, so I don't have the exact error log, but it was saying I cannot cast type T to Unit. Basically, I was trying to make this function generic...

fun screen(bot: Bot.()-> Unit): Bot = Bot().apply(bot())

I was so close. Ended up using this:

Inline fun <reified T: Any> screen(bot: T.() -> Unit): T? = T::class.java.newInstance().apply { bot() }

Then I can use it like

screen<ScreenObject> { functionsFromScreenObjectClass }

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