Hi! I'm not sure of which channel is best for this...

# getting-started

[Matthieu Stombellini]

Hi! I'm not sure of which channel is best for this, but I'm trying to get provideDelegate to work with generic output types. Basically, what I'm trying to do is the following setup:

class Producer {
    inline fun <reified T> create(): ReadOnlyProperty<Any, T> {
        println("Creating a property with create(), return type is ${T::class}")
        TODO()
    }
    
    inline operator fun <reified T> provideDelegate(thisRef: Any, prop: KProperty<*>): ReadOnlyProperty<Any, T> {
        println("Creating a property with provideDelegate, return type is ${T::class}")
        TODO()
    }
}

class MyClass(producer: Producer) {
    val one: String by producer.create()
    //val two: String by producer
}

While the val one works perfectly fine, if I uncomment val two, it no longer compiles. Is there any way to do this? Kotlin Playground link: https://pl.kotl.in/vXOAoeauS
Compilation fails with:

Property delegate must have a 'provideDelegate(MyClass, KProperty<*>)' method. None of the following functions is suitable: public final inline operator fun <reified T> provideDelegate(thisRef: Any, prop: KProperty<*>): ReadOnlyProperty<Any, ???> defined in Producer

[Youssef Shoaib [MOD]]

Looks the same as KT-17440. Only workaround seems to be using a method. If you need access to the KProperty inside create, then make create return a PropertyDelegateProvider instead like so:

import kotlin.reflect.*
import kotlin.properties.*

class Producer {
    inline fun <reified T> create(): PropertyDelegateProvider<Any?, ReadOnlyProperty<Any?, T>>  = PropertyDelegateProvider { _, prop ->
        println("Creating a property with provideDelegate, return type is ${T::class}")
        TODO()
    }
}

class MyClass(producer: Producer) {
    val one: String by producer.create()
    val two: String by producer.create()
}

fun main() {
    val obj = MyClass(Producer()) // will fail immediately because of the TODO()s, that's normal
}