Kotlin: Adding generics to a List<Any>

I have a generic object:

data class MyObject<T>(
    val entity: T
)

I want to concatenate two lists of these objects, with different types T, and return them.

I tried

fun concatLists(): List<MyObject<Any>> {
val listOfAs = listOf(MyObject<A>())
val listOfBs = listOf(MyObject<B>())

return mutableListOf<MyObject<Any>>().also {
            it.addAll(listOfAs)
            it.addAll(listOfBs)
        }
}

however I get the error:

Type mismatch.
Required:
Collection<MyObject<Any>>
Found:
List<MyObject<A>>

I don't understand why this error is being thrown as I thought Collection was a child of List, and type A was a child of Any, that this would work.

Solution

For your use case you can use star projection, like

fun concatLists(): List<MyObject<*>> {
    val listOfAs = listOf(MyObject(A()))
    val listOfBs = listOf(MyObject(B()))

    return mutableListOf<MyObject<*>>().also {
        it.addAll(listOfAs)
        it.addAll(listOfBs)
    }
}