run

Like let, run is another scoping function from the standard library. Basically, it does the same: executes a code block and returns its result. The difference is that inside run the object is accessed by this. This is useful when you want to call the object's methods rather than pass it as an argument.

fun main() {
    fun getNullableLength(ns: String?) {
        println("for \"$ns\":")
        ns?.run {                                                  // 1
            println("\tis empty? " + isEmpty())                    // 2
            println("\tlength = $length")                           
            length                                                 // 3
        }
    }
    getNullableLength(null)
    getNullableLength("")
    getNullableLength("some string with Kotlin")
}

1. Calls the given block on a nullable variable.
2. Inside run, the object's members are accessed without its name.
3. run returns the length of the given String if it's not null.