Can I cast from a Generic type to an Enum in C#?

Question

I'm looking to write a utility function that gets a integer from the database and returns a typed Enum to the application.

Here is what I tried to do (note I pass in a datareader and columnname instead of the int in my real function)...

    public static T GetEnum<T>(int enumAsInt)
    {
        Type enumType = typeof(T);

        Enum value = (Enum)Enum.ToObject(enumType, enumAsInt);
        if (Enum.IsDefined(enumType, value) == false)
        {
            throw new NotSupportedException("Unable to convert value from database to the type: " + enumType.ToString());
        }

        return (T)value;
    }

But it won't let me cast (T)value saying "Cannot convert type 'System.Enum' to 'T'.

Also I've read quite a bit of mixed reviews about using Enum.IsDefined. Performance wise it sounds very poor. How else can I guarentee a valid value?

Thanks!

Answer 1

Like this:

return (T)(object)value;

Answer 2

Change this:

Enum value = (Enum)Enum.ToObject(enumType, enumAsInt);

to this:

T value = (T)Enum.ToObject(enumType, enumAsInt);

and remove the cast :)

Answer 3

Can you put a constraint on the generic type to force it to derive from Enum? I can't remember if all enum types actually use Enum as a base class.