assertIs

Common
JVM
JS
Native
1.5
fun <reified T> assertIs(
    value: Any?,
    message: String? = null
): T

(source)

Asserts that value is of type T, with an optional message.

Note that due to type erasure the type check may be partial (e.g. assertIs<List<String>>(value) only checks for the class being List and not the type of its elements because it's erased).