Hi, is it possible to resolve generic types with k...

# koin

[holgerbrandl]

Hi, is it possible to resolve generic types with koin? I've tried with

import org.koin.core.KoinComponent
import org.koin.core.context.startKoin
import org.koin.dsl.module

class State<T>(val initialValue: T, name: String? = null)

fun main() {
    val sim = module(createdAtStart = true) {

        single{ State("red") }
        single{ State(false) }
    }

    startKoin() { modules(sim) }

    val koin = (object : KoinComponent {}).getKoin()
    val boolState = koin.get<State<Boolean>>()
    val stringState = koin.get<State<Boolean>>()
}

but this fails with

Exception in thread "main" org.koin.core.error.DefinitionOverrideException: Definition '[Single:'State']' try to override existing definition. Please use override option or check for definition '[Single:'State']'

[tynn]

It's not possible directly. Koin uses KClass as key and thus looses the generic parameter types.

[tynn]

I worked around it by defining extensions using typeOf to create a custom Qualifier with this type: TypeQualifier(KType,Qualifier)

[holgerbrandl]

Thanks for sharing your insights @tynn. Could you provide an example to illustrate how typeOf can be used here?

[tynn]

Sure...
The qualifier type should look similar to this one...

data class TypedQualifier(
  private val type: KType,
  private val qualifier: Qualifier,
) : Qualifier {
  override val value = "$type:${qualifier.value}"
}

Then just override the DSL to support it...

inline fun <reified T> inject2<T>(
  qualifier: Qualifier,
  ...,
) = inject<T>(
  TypedQualifier(typeOf<T>(), qualifier),
  ...,
)

[holgerbrandl]

How does this differ from the existing TypeQualifier in the koin API? With that we can doe already

single(TypeQualifier(Boolean::class)){ State<String>("red") }

[tynn]

TypeQualifier uses KClass<T> while the implementation above uses KType which doesn't loose the generic types.

[deviant]

kodein lib can handle types. they use some reflection magic to retrieve a type

[holgerbrandl]

Indeed & thanks @deviant this is possible with kodein. Since it seems to be an implementation issue, I've created https://github.com/InsertKoinIO/koin/issues/976