public static IEnumerable <DTask> generate(this DUrlTemplate source)
        {
            var data_bag = source.DataBag;
            var url      = source.Url;

            return(data_bag.MinValue
                   .to(data_bag.MaxValue)
                   .Select(x =>
            {
                var task = new DTask();
                var uri = url.Replace(data_bag.Key, x.ToString());
                return task.init(new DSite()
                {
                    Host = source.Host,
                    Uri = uri,
                });
            }));
        }
 public static bool empty(this DUrlTemplate source)
 {
     return(string.IsNullOrEmpty(source.Url));
 }