Just Generic Code Snippet for reference

gen_code_snippet.kt

// If we use out / in <out T> / <in T> restricts for getter and setter. Also, variance can be used on Classes and Interfaces.

abstract class Test<T> {
    abstract fun getTest(input: T): T
}

class TestImpAbs : Test<Int>() {
    override fun getTest(input: Int): Int {
        return 0
    }
}

interface TestClass<T> {
    fun getTest(): T
}

class TestImp : TestClass<String> {
    override fun getTest(): String {
        return ""
    }
}

// Can't use Variance (out/in) on the function.
fun <T> test(classa: T): T {
    return classa
}