Is there a way to pass these references without ha...

# announcements

[Marc Knaup]

Is there a way to pass these references without having to repeat User:: over and over again? 🤔

[Gabriel Shanahan]

I actually dealt with that in a small library I made, take a look: https://github.com/gabrielshanahan/moroccode. The basic trick is to define lambdas with receivers (the receiver being the User object), then you can just use the field names themselves. Hope this helps

[Marc Knaup]

Thanks Gabriel, but I do need the KProperty and I don’t have an instance of User here. Thus I cannot call anything where User is a receiver parameter.

[Gabriel Shanahan]

can you show me the signature of conversion<T>?

[Gabriel Shanahan]

however, if you need the KProperty, I'm afraid there's not much you can do

[Marc Knaup]

inline fun <reified Value : Any> conversion(noinline configure: Conversion<Value>.() -> Unit) =
			conversion(valueClass = Value::class, configure = configure)

[Gabriel Shanahan]

class Test(val a: Int, b: Int)

fun myFun(test: Test, f:Test.() -> Unit) {
    test.f()
}

myFun(Test(1, 2)) {
    println((::a).javaClass)
}

[Gabriel Shanahan]

I tried out this real quick:

[Gabriel Shanahan]

but got a "References to variables aren't supported yet" error. So..maybe someday 🙂

[Marc Knaup]

and you need an instance here 🙂

[Gabriel Shanahan]

I didn't understand what you meant when you said that the first time, now I get that you're working with the actual KProperties themselves. Sorry I can't help you more

[Marc Knaup]

Thanks for trying though!

[robstoll]

you can do it but intellij does not support it

class A {
    val a = 1
    fun foo() = "a"
}

fun bar(f: A.() -> Unit) = 1

fun test() {
    bar { ::a }
}

[Marc Knaup]

@robstoll same problem here. I don’t have an instance of A.

[robstoll]

ah right, upvote the following feature request 😉
https://youtrack.jetbrains.com/issue/KT-23777

[Marc Knaup]

Wouldn’t that make it worse in my case? 😄

[Marc Knaup]

7x field(typeOf(???)::someProp)

[Marc Knaup]

That’s worse than repeating the name

[robstoll]

😄

[Marc Knaup]

Basically we’d need to be able to scope into a type instead of a value.

withType<User> {
   field(::birthday)
}

I guess that would change the language a lot 😅

[earroyoron]

Apply?

[Marc Knaup]

You can’t apply() on a class, only on an instance.

[Marc Knaup]

User.apply { … } won’t work (or use the companion, which is not intended)

[robstoll]

I would have imagined that typeOf give some kind of meta-structure for the corresponding type (just saw that typeOf now actually exists in Kotlin -> KType). However, it is dumb and you cannot do something like:

fun bar(f: KType<A>.() -> Unit) = 1

@ExperimentalStdlibApi
fun test() {
    bar { ::a }(typeOf(A))
}

[Marc Knaup]

That looks super confusing 😅

[robstoll]

ok, for you, to lower the confusion 😉

with(typeOf(A)){
    ::a
}

which is what you wanted no?

[Marc Knaup]

Kinda, yeah.

[Marc Knaup]

KType isn’t generic though :)

[Marc Knaup]

And ::a potentially ambiguous now.
Is it a property of KType or of the type that KType is referring to? ^^

[robstoll]

you are right 🙂 that's something which would need to be specified. easiest would be if you can do typeOf(A).a which returns KProperty<Int>

[robstoll]

but yeah.. this does not exist so it does not really make sense to dream about it, right?

[Marc Knaup]

Yeah, unlikly that it’ll be valuable enough so that it’s worth introducing a lot of new complexity.

[TormentedDan]

Hmm, maybe you can use contracts?

[TormentedDan]

https://devdocs.io/kotlin/api/latest/jvm/stdlib/kotlin.contracts/index

[TormentedDan]

On second tought, I don't think contracts would be useful here. Tbh, it seems like this is out of reach at least for now