Kotlin functions to allow persisting a Set<Serializable> to/from zipped file (good for prototyping and restarting processes)

setpersist.kt

/** Save/load any Set<Serializable>, works easily with your simple data class */
inline fun Set<out Serializable>.save(fileName:String="persist_${javaClass.simpleName}.ser.gz") {
    val tmpPath = Files.createTempFile(fileName, ".tmp")
    ObjectOutputStream(GZIPOutputStream(Files.newOutputStream(tmpPath, StandardOpenOption.CREATE, StandardOpenOption.WRITE))).use {
        println("Persisting Set<${javaClass.simpleName}> to $fileName containing ${this.size} entries.")
        it.writeObject(this)
    }
    Files.move(tmpPath, Paths.get(fileName), StandardCopyOption.REPLACE_EXISTING)
}

inline fun <reified T> MutableSet<in T>.load(fileName:String="persist_${javaClass.simpleName}.ser.gz") {
    try {
        ObjectInputStream(GZIPInputStream(FileInputStream(fileName))).use {
            val loaded = it.readObject() as Collection<*>
            println("Loading collection with ${loaded.size} entries.")
            loaded.forEach { if (it !is T) throw IllegalArgumentException() }
            this.addAll(loaded.filterIsInstance<T>())
        }
    } catch (e:IOException) {
        println("Unable to load($fileName): ${e.localizedMessage}")
    }
}

// Customize to your needs
data class YourDataClass(val sourceFile: String, val frame: Int, val x: Int, val y: Int, val width: Int, val height: Int) : Serializable

// Long running app has
val yourStuff = mutableSetOf<YourDataClass>()
yourStuff.load()
// Skip doing stuff that is already done, do new stuff, and every so often persist with 
yourStuff.save()