Variance.kt

// Why do we need variance

// Invariant class List, just like in Java
class List<T> { /* normal list */ }

fun printContents(list: List<Any>) {
    for (item in list) {
        println(item)
    }
}

fun test() {
    val list: List<String> = listOf("a", "b")
    
    printContents(list) // ERROR: List<String> is not a subtype of List<Any>
}

Just for the record. On the matter of variance in Java (which is called use-site variance): https://prezi.com/lnw_oiv1gs-j/java-8-vs-kotlin/