التفويض إلى الأعضاء

تركيب السلوك

دوران وفئة واحدة

interface Reader { fun read(): String }
interface Writer { fun write(s: String): String }

class FileReader : Reader { override fun read() = "contents" }
class FileWriter : Writer { override fun write(s: String) = "wrote " + s }

class FileIO(r: Reader, w: Writer) : Reader by r, Writer by w

fun main() {
    val io = FileIO(FileReader(), FileWriter())
    println(io.read())
    println(io.write("data"))
}

مفوَّضون متعددون

interface Logger { fun log(m: String): String }
interface Validator { fun valid(m: String): Boolean }

class ConsoleLogger : Logger { override fun log(m: String) = "LOG: " + m }
class LengthValidator : Validator { override fun valid(m: String) = m.isNotEmpty() }

class Service(l: Logger, v: Validator) : Logger by l, Validator by v

fun main() {
    val s = Service(ConsoleLogger(), LengthValidator())
    println(s.valid("hi"))
    println(s.log("started"))
}

تخزين المفوَّض كعضو

interface Cache { fun get(k: String): String }

class MapCache : Cache {
    override fun get(k: String) = "value-of-" + k
}

class TracingCache(private val inner: Cache) : Cache by inner {
    override fun get(k: String): String {
        println("lookup " + k)
        return inner.get(k)
    }
}

fun main() {
    println(TracingCache(MapCache()).get("id"))
}

مزج التفويض مع الحالة الخاصة

interface Engine { fun start(): String }
class V8 : Engine { override fun start() = "vroom" }

class Car(e: Engine) : Engine by e {
    var doors = 4
    fun honk() = "beep"
}

fun main() {
    val c = Car(V8())
    println(c.start())
    println(c.honk())
    println(c.doors)
}

تبديل التطبيقات

interface Notifier { fun send(msg: String): String }
class EmailNotifier : Notifier { override fun send(msg: String) = "email: " + msg }
class SmsNotifier : Notifier { override fun send(msg: String) = "sms: " + msg }

class Alerts(n: Notifier) : Notifier by n

fun main() {
    println(Alerts(EmailNotifier()).send("hi"))
    println(Alerts(SmsNotifier()).send("hi"))
}

التفويض إلى خاصية

interface Greeter { fun greet() = "hi" }
class DefaultGreeter : Greeter

class Page : Greeter by DefaultGreeter()

fun main() {
    println(Page().greet())
}

تجنب مشكلة الماسة

interface A { fun a() = "A" }
interface B { fun b() = "B" }
class AImpl : A
class BImpl : B

class Combined : A by AImpl(), B by BImpl()

fun main() {
    val c = Combined()
    println(c.a() + c.b())
}

التصميم من أجل التركيب

مراجعة التفويض إلى الأعضاء

التالي: مقارنة مباشرة

اختبار سريع

مراجعة