unless is not a built-in keyword in Kotlin, but it can be implemented using an if-else statement. The unless statement can be used in place of an if statement where it evaluates a boolean condition and executes its code block if the condition is false.
Here's an example:
fun main() {
val number = 10
unless(number > 20) { // Call the unless function and pass in the boolean expression
println("The number is less than or equals to 20.")
}
}
fun unless(condition: Boolean, body: () -> Unit) {
if (!condition) {
body()
}
}
Output:
The number is less than or equals to 20.
In the code above, we first define the unless function which takes in two parameters: a boolean condition and a lambda function body. The unless function then invokes the body function if the given condition is false.
In the main function, we then use the unless function to output a message if the number variable is less than or equals to 20.