Is it possible to provide multiple delegate types with a single class?

Question

I'd like to provide multiple different delegates from a single class, with differing types. For example:

class A {
  val instanceOfB = B()

  val aNumber: SomeType by instanceOfB
  val anotherNumber: SomeOtherType by instanceOfB
}

class B {
  operator fun <T1: SomeType> getValue(thisRef: Any?, property: KProperty<T1>): T1 {
    return SomeType()
  }

  operator fun <T2: SomeOtherType> getValue(thisRef: Any?, property: KProperty<T2>): T2 {
    return SomeOtherType()
  }
}

open class SomeType {}
open class SomeOtherType {}

This example gives the following compiler error: 'operator' modifier is inapplicable on this function: second parameter must be of type KProperty<*> or its supertype

Is there some way to specify the generic type arguments such that I can achieve this?

Answer 1

Only way I got it to compile and run, albeit I highly advise against using it aside from proof of concept since inline will generate a lot of trash code, and each getValue call will run through entire when statement:

class B {
  inline operator fun <reified T : Any>getValue(thisRef: Any?, property: KProperty<*>): T {
    return when(T::class.java){
        SomeType::class.java -> SomeType() as T
        SomeOtherType::class.java-> SomeOtherType() as T
        else -> Unit as T
    }
  }
}

There's also operator fun provideDelegate that generates the delegates, but it's limited to 1 return value as well. I don't think there's elegant / supported way to doing what you need right now.