Question

I’m trying to get a generic interface with implentation for handling my xml:
IXmlService

List<T> Load<T>() where T : class;

XmlService

public List<T> Load<T>() where T : class {
    Type type = typeof(T);

    if (type == typeof(TicketData)) { return XmlTicketService.LoadInternal(); } // Error: Unable to cast from List<TicketData> to List<T>

And the XmlTicketService.LoadInternal() knows the type and should return to Service

internal static List<TicketData> LoadInternal() {
    List<TicketData> result = new List<TicketData>();

    ThreadPool.QueueUserWorkItem(
        delegate {
            try {
                XDocument data = XDocument.Load(_xmlPath);
                var query = (from element in data.Root.Descendants("Ticket")
                             select new TicketData() {

Hope u have and advices for me 🙂

Answer 1

Well, in this case you can just cast, going via object:

if (typeof(T) == typeof(TicketData))
{ 
    return (List<T>) (object) XmlTicketService.LoadInternal();
}

The object cast first basically forces the compiler to treat it as a “normal” cast.

… but personally I think that raises a design smell, where you should probably be creating a generic interface with a non-generic method, and implementing ILoadable<TicketData> or whatever. Basically your method isn’t really generic – it has specific handling for specific types, which should always make you question whether your design is really appropriate.