measuretimeContract.kt

@ExperimentalContracts
fun main(args: Array<String>) {
    var assign: String
    val time = measureTimeMillis {
        assign = "Value Assigned"
    }
    println("$time ms. spent assigning: '$assign'")
}

@ExperimentalContracts
private inline fun measureTimeMillis(block: () -> Unit): Long {
    contract {
        callsInPlace(block, kotlin.contracts.InvocationKind.EXACTLY_ONCE)
    }
    val start = System.currentTimeMillis()
    block()
    return System.currentTimeMillis() - start
}