DEPRECATED example how to obtain KType instance from reified T. Please use "typeOf" since 1.3.40!

getKType.kt

import java.lang.reflect.*
import kotlin.reflect.KClass
import kotlin.reflect.KType
import kotlin.reflect.KTypeProjection
import kotlin.reflect.KVariance
import kotlin.reflect.full.createType

// --- Interface ---

inline fun <reified T : Any> getKType(): KType =
        object : SuperTypeTokenHolder<T>() {}.getKTypeImpl()

// --- Implementation ---

@Suppress("unused")
open class SuperTypeTokenHolder<T>

fun SuperTypeTokenHolder<*>.getKTypeImpl(): KType =
        javaClass.genericSuperclass.toKType().arguments.single().type!!

fun KClass<*>.toInvariantFlexibleProjection(arguments: List<KTypeProjection> = emptyList()): KTypeProjection {
    // TODO: there should be an API in kotlin-reflect which creates KType instances corresponding to flexible types
    // Currently we always produce a non-null type, which is obviously wrong
    val args = if (java.isArray()) listOf(java.componentType.kotlin.toInvariantFlexibleProjection()) else arguments
    return KTypeProjection.invariant(createType(args, nullable = false))
}

fun Type.toKTypeProjection(): KTypeProjection = when (this) {
    is Class<*> -> this.kotlin.toInvariantFlexibleProjection()
    is ParameterizedType -> {
        val erasure = (rawType as Class<*>).kotlin
        erasure.toInvariantFlexibleProjection((erasure.typeParameters.zip(actualTypeArguments).map { (parameter, argument) ->
            val projection = argument.toKTypeProjection()
            projection.takeIf {
                // Get rid of use-site projections on arguments, where the corresponding parameters already have a declaration-site projection
                parameter.variance == KVariance.INVARIANT || parameter.variance != projection.variance
            } ?: KTypeProjection.invariant(projection.type!!)
        }))
    }
    is WildcardType -> when {
        lowerBounds.isNotEmpty() -> KTypeProjection.contravariant(lowerBounds.single().toKType())
        upperBounds.isNotEmpty() -> KTypeProjection.covariant(upperBounds.single().toKType())
        // This looks impossible to obtain through Java reflection API, but someone may construct and pass such an instance here anyway
        else -> KTypeProjection.STAR
    }
    is GenericArrayType -> Array<Any>::class.toInvariantFlexibleProjection(listOf(genericComponentType.toKTypeProjection()))
    is TypeVariable<*> -> TODO() // TODO
    else -> throw IllegalArgumentException("Unsupported type: $this")
}

fun Type.toKType(): KType = toKTypeProjection().type!!

// --- Usage example ---

fun main(args: Array<String>) {
    println(getKType<List<Map<String, Array<Double>>>>())
    println(getKType<List<*>>())
    println(getKType<Array<*>>())
    println(getKType<Array<Array<String>>>())
    println(getKType<Unit>())
}

@hinls1007 @JLLeitschuh This code is licensed under WTFPL Version 2.

createType doesn't seem to exist anymore