dynamic_handler_routing.kt

package org.example

import java.io.File
import java.util.*

typealias ResultType = String


interface Processor<T : Any> {
    fun getType(): Class<T>
    fun handle(specimen: T): ResultType


    fun canHandle(specimen: Any): Boolean {
        return getType().isInstance(specimen)
    }

    companion object {
        private val processorList: List<Processor<*>> = listOf(
            DateProcessor,
            FileProcessor,
            CharSequenceProcessor
        )

        fun <ProcessorType : Any, SpecimenType : ProcessorType> getTheRightProcessor(specimen: SpecimenType): Processor<ProcessorType> {
            val matchingProcessor: Processor<*> = processorList.first {
                it.canHandle(specimen)
            }

            @Suppress("UNCHECKED_CAST")
            return matchingProcessor as Processor<ProcessorType>
        }

        fun <SpecimenType : Any> handle(specimen: SpecimenType) =
            getTheRightProcessor(specimen).handle(specimen)

        fun <SpecimenType : Any> getHandler(specimen: SpecimenType): () -> ResultType {
            return {
                handle(specimen)
            }
        }

    }
}


object DateProcessor : Processor<Date> {

    override fun getType(): Class<Date> {
        return Date::class.java
    }

    override fun handle(specimen: Date): ResultType {
        return "handler = $this; date = $specimen"
    }

}

object FileProcessor : Processor<File> {

    override fun getType(): Class<File> {
        return File::class.java
    }

    override fun handle(specimen: File): ResultType {
        return "handler = $this; path = ${specimen.path}; exists = ${specimen.exists()}"
    }

}

object CharSequenceProcessor : Processor<CharSequence> {

    override fun getType(): Class<CharSequence> {
        return CharSequence::class.java
    }

    override fun handle(specimen: CharSequence): ResultType {
        return "handler = $this; length = ${specimen.length}"
    }

}


fun main() {
    val sampleDate = Date()
    val sampleFile = File("/windows/system32")
    val sampleString = "This is a String which is-a CharSequence"

    println("sampleDate: ${Processor.handle(sampleDate)}")
    println("sampleFile: ${Processor.handle(sampleFile)}")
    println("sampleString: ${Processor.handle(sampleString)}")
}