value property
      
      T
      get
      value
      
    
override
    Get current value
Implementation
T get value => _value;
      
      set
      value
      (T val) 
      
    
override
    Set value
Implementation
set value(T val) {
  if (_value == val) {
    return;
  }
  T old = _value;
  _value = val;
  _change.add(Change<T>(val, old, _curBatch));
}