Function extension, attribute extension and non empty type extension in kotlin

val myStr: String = "AAA"
// Extended attributes 
val String.myInfo: String
    get() = "yuknight"

fun String.showPrintln(): String {
    println(" Printout , Parallel chain call , The content is :$this")
    return this
}

val String.strValue: String
    get() = " At present ${System.currentTimeMillis()}, Call once , The value is :$this, The length is $length"

// Yes  String?== Function extension of null type 
fun String?.outputStrValueF(defaultValue:String) = println(this ?: defaultValue)
fun String?.outputStrValueFget(defaultValue: String) = if (this == null) defaultValue else this

fun main(){
    val str:String = "ABC"
    println(str.myInfo)
    // spread function 
    str.showPrintln().showPrintln().showPrintln()
    // Extended attributes 
    str.myInfo.showPrintln().showPrintln()
    "yuknight".strValue.showPrintln().showPrintln()
    /****************************************/
    val infoValue:String? = null //infoValue It's a nullable type  String String?== Null type 
    infoValue.outputStrValueF(" The default value is 1")

    val name = "yuknight"
    name.outputStrValueFget(" The default value is 2")

    println(infoValue.outputStrValueFget(" The default value is 3"))
    println(name.outputStrValueFget(" The default value is 4"))
}