import java.lang.ref.WeakReference


fun main(args: Array<String>) {

    var fancyClass3: FancyClass? = FancyClass.get()
    gc()
    fancyClass3 = null
    gc()
    Thread.sleep(1000)

    var fancyClass: FancyClass? = FancyClass("should be garbage collectible")
    gc()
    fancyClass = null
    gc()
    Thread.sleep(1000)

    var fancyClass2: FancyClass? = FancyClass.get()
    gc()
    fancyClass2 = null
    gc()
    Thread.sleep(1000)
}

fun gc() {
    var obj: Any? = Any()
    val ref = WeakReference<Any>(obj)
    obj = null
    while (ref.get() != null) {
        System.gc()
    }
}

class FancyClass(private val description: String) {

    protected fun finalize() {
        println("Goodbye my darling ($this : $description)")
    }

    companion object : Provider<FancyClass>() {
        override fun create(): FancyClass {
            return FancyClass("shouldn't be garbage collectible")
        }
    }

}

/**
 * Created by nicoladefiorenze on 22/03/18.
 */
abstract class Provider<T> {

    protected var original: T? = null

    var mocked: T? = null

    protected abstract fun create(): T

    fun get(): T = mocked ?: original ?: create()
            .apply { original = this }

    fun lazyGet(): Lazy<T> = lazy { get() }

}