kotlin标准库扩展之 let run apply also（一）

The Kotlin standard library function let can be used for scoping and null-checks.
 When called on an object, let executes the given block of code and 
 returns the result of its last expression. 
The object is accessible inside the block by the reference it.

fun letFun() {
    val empty = "test".let {
        customPrint(it)
    }
    println("is empty: $empty")
    fun printNonNull(str: String?) {
        println("Printing \"$str\"")
        str?.let {
            print("\t")
            customPrint(it)
            println()
        }
    }
    printNonNull(null)
    printNonNull("my string")
}

fun runFun() {
    fun getNullableLengt(ns: String) {
        println("for \"$ns\":")
        ns.run {
            println("\tis empty? " + this.isEmpty())
            println("\tlenght =${this.length}")
        }
    }
}