update method

Implementation

bool update() {
  ++cycle;
  depsTail = null;
  flags = 5 /* Mutable | RecursedCheck */;

  final prevSub = setActiveSub(this);
  try {
    final oldValue = cachedValue;
    return oldValue != (cachedValue = getter(oldValue));
  } finally {
    activeSub = prevSub;
    flags &= -5 /* RecursedCheck */;
    purgeDeps(this);
  }
}