private static IReadScalar <int> getIndex(IReadScalar <INotifyCollectionChanged> sourceScalar)
{
IReadScalar <IList> listComputing = sourceScalar.Using(s => (IList)s.Value);
Expression <Func <int> > indexExpression = () => listComputing.Value != null && listComputing.Value.Count > 0 ? listComputing.Value.Count - 1 : 0;
return(indexExpression.Computing());
}