أنماط عملية

نمط المزيّن

مكوّن أساسي

interface DataSource {
    fun fetch(): String
}

class NetworkSource : DataSource {
    override fun fetch() = "raw-data"
}

fun main() {
    println(NetworkSource().fetch())
}

مزيّن التسجيل

interface DataSource { fun fetch(): String }
class NetworkSource : DataSource { override fun fetch() = "raw-data" }

class LoggingSource(private val inner: DataSource) : DataSource by inner {
    override fun fetch(): String {
        println("fetching...")
        val result = inner.fetch()
        println("done")
        return result
    }
}

fun main() {
    println(LoggingSource(NetworkSource()).fetch())
}

مزيّن التخزين المؤقت

interface DataSource { fun fetch(): String }
class NetworkSource : DataSource { override fun fetch() = "raw-data" }

class CachingSource(private val inner: DataSource) : DataSource by inner {
    private var cached: String? = null
    override fun fetch(): String {
        return cached ?: inner.fetch().also { cached = it }
    }
}

fun main() {
    val s = CachingSource(NetworkSource())
    println(s.fetch())
    println(s.fetch()) // served from cache
}

تكديس المزيّنات

interface DataSource { fun fetch(): String }
class NetworkSource : DataSource { override fun fetch() = "raw-data" }

class LoggingSource(private val inner: DataSource) : DataSource by inner {
    override fun fetch(): String { println("log"); return inner.fetch() }
}
class CachingSource(private val inner: DataSource) : DataSource by inner {
    private var c: String? = null
    override fun fetch() = c ?: inner.fetch().also { c = it }
}

fun main() {
    val s = LoggingSource(CachingSource(NetworkSource()))
    println(s.fetch())
    println(s.fetch())
}

مزيّن التحقق

interface Processor { fun process(input: String): String }
class UpperProcessor : Processor { override fun process(input: String) = input.uppercase() }

class ValidatingProcessor(private val inner: Processor) : Processor by inner {
    override fun process(input: String): String {
        require(input.isNotBlank()) { "empty input" }
        return inner.process(input)
    }
}

fun main() {
    println(ValidatingProcessor(UpperProcessor()).process("hello"))
}

غلاف مجموعة للقراءة فقط

class SummarizedList(private val inner: List<Int>) : List<Int> by inner {
    fun total() = inner.sum()
}

fun main() {
    val list = SummarizedList(listOf(1, 2, 3))
    println(list.size)
    println(list.total())
}

عدّ الاستدعاءات

interface Service { fun call(): String }
class RealService : Service { override fun call() = "ok" }

class CountingService(private val inner: Service) : Service by inner {
    var calls = 0
        private set
    override fun call(): String {
        calls++
        return inner.call()
    }
}

fun main() {
    val s = CountingService(RealService())
    s.call(); s.call()
    println(s.calls)
}

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