Idiomatic kotlin delegate method of using weak reference and soft reference in Java.

ReferencesDelegates.kt

package delegates

import java.lang.ref.SoftReference
import java.lang.ref.WeakReference
import kotlin.properties.ReadWriteProperty
import kotlin.reflect.KProperty


fun <T>weakReference(tIn: T? = null): ReadWriteProperty<Any?, T?> {
    return object : ReadWriteProperty<Any?, T?> {
        var t = WeakReference<T?>(tIn)
        override fun getValue(thisRef: Any?, property: KProperty<*>): T? {
            return t.get()
        }

        override fun setValue(thisRef: Any?, property: KProperty<*>, value: T?) {
            t = WeakReference(value)
        }
    }
}

fun <T>softReference(tIn: T? = null): ReadWriteProperty<Any?, T?> {
    return object : ReadWriteProperty<Any?, T?> {
        var t = SoftReference<T?>(tIn)
        override fun getValue(thisRef: Any?, property: KProperty<*>): T? {
            return t.get()
        }

        override fun setValue(thisRef: Any?, property: KProperty<*>, value: T?) {
            t = SoftReference(value)
        }
    }
}

class Employee(val name: String, val id: String)

fun main() {
    // This example may not work a expected, mostly because System.gc() need not trigger garbage collection.
    // It is just a directive to the JVM but it need not trigger GC.
    // There is no other way to simulate gc call other than triggering gc in a loop
    run {
        var employeeWeak: Employee? by weakReference(null)
        employeeWeak = Employee("alok", "sjdfsdkjfdl")

        println(employeeWeak?.name)
        System.gc() // This may not trigger but it happens in JVM long running processes as needed.
        println(employeeWeak?.name) // May be null if gc has been performed by the JVM.
    }

    run {
        // Remember, soft reference are cleared only when there is a clear memory shortage
        var employeeWeak: Employee? by softReference(Employee("gecko", "sjdfsdkjfd11l"))

        println(employeeWeak?.name)
        System.gc() // This may not trigger but it happens in JVM long running processes as needed.
        println(employeeWeak?.name) // Need not be null. Mostly non-null
    }




}