I am not able to make this simple example of code work:

package com.example

import kotlin.reflect.full.memberProperties

fun main() {
    val person = Person("Alice", 29)
    person::class.memberProperties.forEach {
        println("${it.name} = ${it.get(person)}")
    }
}

data class Person(val name: String, val age: Int)

It should print the list of properties with their values but when executed it throws exception: Argument type mismatch: actual type is 'com.example.Person', but 'CapturedType(out com.example.Person)' was expected.

I am not able to make this simple example of code work:

package com.example

import kotlin.reflect.full.memberProperties

fun main() {
    val person = Person("Alice", 29)
    person::class.memberProperties.forEach {
        println("${it.name} = ${it.get(person)}")
    }
}

data class Person(val name: String, val age: Int)

It should print the list of properties with their values but when executed it throws exception: Argument type mismatch: actual type is 'com.example.Person', but 'CapturedType(out com.example.Person)' was expected.

• kotlin
• reflection

1 Answer 1

You should use Person::class instead of person::class. The latter gives you a KClass<out Person>. From the compiler's point of view, KClass<out Person> can represent a subclass of Person too. This means memberProperties may contain properties exclusive to that (unknown) subclass. Therefore, it is not safe to pass a Person to it.get, because it might not be a property that the instance of Person has.

Of course, in reality Person cannot have subclasses. If you cannot hardcode Person::class (because you do not know the runtime type of person at compile time for some reason), you can use an unchecked cast to convince the compiler.

(person::class as KClass<Any>).memberProperties.forEach {
    println("${it.name} = ${it.get(person)}")
}