data class FunctionWrapper<T>(
    val function: (T) -> Any?
)

fun main() {
    val stringFun = FunctionWrapper<String> { s -> s.trim() }
    val intFun = FunctionWrapper<Int> { s -> s * 2 }
    val funs = listOf(stringFun, intFun)

    val value: Any = "testValue"

    for (f in funs) {
        when (f) {
            is Function<*> -> f.function.invoke(value)  // only allows Nothihng 
        }
    }
}