80 Collection change notifications

A subscription on a collection field sees in-place List mutations as old/new value snapshots. Closing it stops notifications, not later list changes.

import std.observation.onChange

class Tasks { List<String> titles = [] }

main() {
  Tasks tasks = Tasks()
  var subscription = tasks.titles.onChange {
    printLine("${oldValue.size()} -> ${newValue.size()}")
  }
  tasks.titles.add("Learn")
  tasks.titles.add("Build")
  subscription.close()
  tasks.titles.add("Publish")
  printLine(tasks.titles.size())
}

Expected output:

0 -> 1
1 -> 2
3

Try it: Replace the list with an equal list and inspect whether it notifies.

Precise rules: Reference.