Re: ignorance: customizable immutables?

so a new type of A is constructed not AStar.


In that case, I probably misunderstood the question. Are we assuming here 
that there is some kind of generic scheme that returns new immutables, 
simply based on the inferred type of the instance and the new values?

I had something along these lines in mind:

class A(v: Int = 0) {
  val value = v
  def foo = "normal"
  def withValue(newValue: Int = value) = new A(newValue)
}

class AStar(v: Int = 0) extends A(v) {
  override def foo = "different"
  override def withValue(newValue: Int = value) = new AStar(newValue)
}

scala> val transformed = List(new A, new AStar) map { _.withValue(42) }
transformed: List[A] = List(A@16c933d, AStar@7f368a85)

scala> transformed foreach { a => println(a.value + ", " + a.foo) }
42, normal
42, different

This seems to me to be in line with the notion of "immutables that respect 
whatever customization has been done", but requires the operation that 
returns the new immutable to be overridden for each customizing class. That 
may well not count as a "concise and robust" scheme, indeed.

Regards

ap

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