Exceptions and Defensive Coding

Require-Style Checks

Check a precondition and return a clear rejection result.

Require-Style Checks

RequireChecks.kt 
fun labelAmount(amount: Int): String {
    if (amount <= 0) {
        return "rejected"
    }
    return "amount:$amount"
}

fun main() {
    val amount = 
    val label = labelAmount(amount)

    println("amount=$amount")
    println("label=$label")
}

fun labelAmount(amount: Int): String {
    if (amount <= 0) {
        return "rejected"
    }
    return "amount:$amount"
}

fun main() {
    val amount = 
    val label = labelAmount(amount)

    println("amount=$amount")
    println("label=$label")
}

fun labelAmount(amount: Int): String {
    if (amount <= 0) {
        return "rejected"
    }
    return "amount:$amount"
}

fun main() {
    val amount = 
    val label = labelAmount(amount)

    println("amount=$amount")
    println("label=$label")
}
precondition A precondition check keeps invalid data out of the main calculation.