Kotlin委托Delegate托管by

Kotlin委托Delegate托管by

import kotlin.reflect.KProperty

fun main() {
    var user: String by MyDelegate()
    user = "fly"
    println(user)
}

class MyDelegate {
    private var v: String? = null

    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
        return "property='${property.name}' getValue ${v}"
    }

    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
        v = value
        println("property='${property.name}' setValue -> $value")
    }
}

property='user' setValue -> fly
property='user' getValue fly

import kotlin.properties.*

fun main() {
    var len: Int by Delegates.observable(0) { prop, oldValue, newValue ->
        println("$oldValue -> $newValue")
    }

    len = 2023
    len = 2024
}

0 -> 2023
2023 -> 2024

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