private static Task <List <T> > CastToListAsync <T>(IEnumerable source)
 {
     return(Task.Run(() => DynamicEnumerableExtensions.CastToList <T>(source)));
 }
 private static Task <T[]> CastToArrayAsync <T>(IEnumerable source)
 {
     return(Task.Run(() => DynamicEnumerableExtensions.CastToArray <T>(source)));
 }