public DirtifiableObject(params string[] derivedProperties)
{
_dirtySubject = new Subject <bool>();
_dirtySubject.ToProperty(this, x => x.IsDirty, out _dirty);
_monitored = new Dictionary <DirtifiableObject, IDisposable>();
var excludes = derivedProperties.Concat(new[] { "IsDirty" }).ToArray();
DataChanged = Changed.Where(e => !excludes.Contains(e.PropertyName));
DataChanged.Subscribe(_ => MarkDirty());
Dirtied = _dirtySubject.Where(x => x).Select(_ => Unit.Default);
}