属性代理

class Delegates{
    val hello by lazy {
        "HelloWorld"
    }
    val hello2 by X()
    var hello3 by X()
}
class X{
    private var value: String? = null
    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
        println("getValue: $thisRef -> ${property.name}")
        return value?: ""
    }
    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String){
        println("setValue, $thisRef -> ${property.name} = $value")
        this.value = value
    }
}
fun main(args: Array<String>) {
    val delegates = Delegates()
    println(delegates.hello)
    println(delegates.hello2)
    println(delegates.hello3)
    delegates.hello3 = "value of hello3"
    println(delegates.hello3)
}