How can I serialize a scala singleton object?

I am trying to serialize a scala singleton object using the built in java object serialization library.

Here's an example of the serializer program:

  object potato extends Serializable {
    var dirt = 5
  }

  def main(args: Array[String]): Unit = {

    val fileName = "potato.sav"
    val potatoOutputStream = new ObjectOutputStream(new FileOutputStream(fileName))
    potato.dirt = 12345
    potatoOutputStream.writeObject(potato)
    potatoOutputStream.close()
}

and here's an example of the deserializer program:

  object potato extends Serializable {
    var dirt = 5
  }

  def main(args: Array[String]): Unit = {

    val fileName = "potato.sav"
    val potatoInputStream = new ObjectInputStream(new FileInputStream(fileName))
    val p = potatoInputStream.readObject.asInstanceOf[potato.type]
    println("potato dirt quantity " + p.dirt)
  }

this prints 5 instead of the expected 12345. I've looked at potato.sav in a hex editor and the number 12345 doesn't even show up, it appears to be a 'scala.runtime.ModuleSerializationProxy' and doesn't contain any field data. In fact, changing any of the numbers in the initializer or the main function results in a byte-for-byte identical serialized file :(

I kind of understand why this might be happening, and that deserializing a singleton object can't (or shouldn't) create another instance, but I would really like to find a way to make this, or something similar work. I don't need to use the built in serialization library, but I need a solution that doesn't require writing a custom serializer/deserializer for each individual singleton object.

Any help would be appreciated. Thanks!

edit: I am using objects here because I want many instances of anonymous subclasses of a certain type, each with custom logic for a DSL.

Unfortunately it seems like using object makes them not serializable because they are implemented as static classes, which java won't serialize. Structural types are out too because in scala 3 you can't access mutable state anymore as some kind of new and unexplained restriction, not to mention the performance problems with structural types.

Solution

Ended up writing my own object serialization routine with some help from apache reflection utils. It's not pretty but it works.

def SerializeMembers(oos: ObjectOutputStream): Unit = {
    val fields = FieldUtils.getAllFields(getClass)
    for (f <- fields) {
        val modifiers = f.getModifiers
        val isNotFinal = (modifiers & Modifier.FINAL) == 0
        if (isNotFinal) {
            f.setAccessible(true)
            oos.writeObject(f.get(this))
        }
    }
}

def DeserialzeMembers(ois: ObjectInputStream): Unit = {
    val fields = FieldUtils.getAllFields(getClass)
    for (f <- fields) {
        val modifiers = f.getModifiers
        val isNotFinal = (modifiers & Modifier.FINAL) == 0
        if (isNotFinal) {
            f.setAccessible(true)
            val obj = ois.readObject()
            f.set(this, obj)
        }
    }
}