private static Expression <Func <TResult> > getValueExpression(
INotifyCollectionChanged source)
{
Expression <Func <TSourceItem> > summarizingExpression = () => source.Summarizing <TSourceItem>().Value;
Expression <Func <int> > countExpression = () => ((IList)source).Count;
return(getExpression(summarizingExpression, countExpression));
}
