Can someone help with this generic extension method?

Question

I'm trying to convert an XElement to either null or whatever type T is supplied.

Here's what I have so far:

public static T? ConvertToNullable<T>(this XElement element) where T : IConvertible
{
    if (element.IsNill())
        return null;
    else
        return (T)element;
}

Error:

The type T must be a non-nullable value type in order to use it as parameter T in the generic type or method System.Nullable<T>

Can this be done or do I have to write a separate extension for bool, byte, int, long, double, decimal, etc.?

Edit

I shouldn't have been using generics for this at all. See my answer below.

Answer 1

Use where T : struct so that your method is restricted to value types (which Nullable only makes sense for).

Answer 2

I'm not sure what you're trying to do here... the only non-nullable types are value types, and XElement is a reference type. So it doesn't make sense to cast it to a Nullable<T>...

Answer 3

Okay, I got it now. I didn't need to use generics at all. I can just leave it as an XElement and do the cast where I call the extension method.

So, my revised code looks like this:

public static XElement NullIfNill(this XElement element)
{
    if (element.IsNill())
        return null;
    else
        return element;
}

Usage example:

var results =
    from
        p in participants.Elements()
    join
        co in conditionOrders.Elements()
        on (int?)p.Element(NS + "conditionOrderId").NullIfNill() equals (int)co.Element(NS + "id")