Extension method on enumeration, not instance of enumeration

Extension methods only work on instances, so it can't be done, but with some well-chosen class/method names and generics, you can produce a result that looks just as good:

public class SelectList
{
    // Normal SelectList properties/methods go here

    public static SelectList Of<T>()
    {
        Type t = typeof(T);
        if (t.IsEnum)
        {
            var values = from Enum e in Enum.GetValues(type)
                         select new { ID = e, Name = e.ToString() };
            return new SelectList(values, "Id", "Name");
        }
        return null;
    }
}

Then you can get your select list like this:

var list = SelectList.Of<Things>();

IMO this reads a lot better than Things.ToSelectList().

No.

The best you can do is put it on a static class, like this:

public static class ThingsUtils { 
    public static SelectList ToSelectList() { ... }
}

Aaronaught's answer is really great, based on that I made the following implementation:

public class SelectList
{
    public static IEnumerable<Enum> Of<T>() where T : struct, IConvertible
    {
        Type t = typeof(T);
        if (t.IsEnum)
        {
            return Enum.GetValues(t).Cast<Enum>();
        }
        throw new ArgumentException("<T> must be an enumerated type.");
    }
}

In my opinion it's a little bit safer, as you can - almost - call it only with Enums, and of course instead of the throw you can simply return null if you want an exception-free version.

Extension method on enumeration, not instance of enumeration

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