Why I keep getting this compile error: `Error:(2, ...

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[Hexa]

Why I keep getting this compile error: Error:(2, 44) Kotlin: Type parameter T is declared as 'in' but occurs in 'invariant' position in type SomeClass<String, T>
But it compiles when I remove the in keyword like this: abstract class A<T>? Given someMethod(item: SomeClass<String, T>) takes T as an input then using in should work in this case?

abstract class A<in T> {
    fun someMethod(item: SomeClass<String, T>) {
        println(item)
    }
}

open class SomeClass<K,V>(
    override val entries: Set<Map.Entry<K, V>>,
    override val keys: Set<K>,
    override val size: Int,
    override val values: Collection<V>
) : Map<K,V>{
    override fun containsKey(key: K): Boolean {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

    override fun containsValue(value: V): Boolean {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

    override fun get(key: K): V? {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

    override fun isEmpty(): Boolean {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }
}

[Kroppeb]

I suggest you look up "invariance". There are quite a few useful resources about it.

[Ruckus]

@Foso I think you posted that to the wrong person

@Hexa Because V is invariant in SomeClass. (Only SomeClass is in the in position, not its parameters.)

[Foso]

@Ruckus you are right, it was the wrong person

[Hexa]

@Ruckus thnx