How to Cast System.ValueType to Generic Type (T) in C#?

Question

I've a C# Code Snippts, which has error as :

Can not convert System.ValueType to T

Please guide me to solve this

here is a code

public static T Add<T>(this Enum type, T value)
{
    try
    {
        return (T) (ValueType) (Convert.ToInt32(type) | (int) (object) value);
    }
    catch (Exception ex)
    {
        throw new ArgumentException(string.Format("Could not append value from enumerated type '{0}'.", (object) typeof (T).Name), ex);
    }
}

now how could i run this error?

Answer 1

You could use Convert.ChangeType

For example,

var result = (ValueType) (Convert.ToInt32(type) | (int) (object) value);
return (T)Convert.ChangeType(result,typeof(T));

Answer 2

The compiler has no idea that T can be upcasted from ValueType as it doesn't know that T is a value type. You'd need to add the struct constraint for that.

public static T Add<T>(this Enum type, T value) where T : struct

Now that intermediate cast to ValueType is equivalent to a cast to object and it compiles.

However , this cast will fail with an InvalidCastException if T is anything else than int or int? (and it can't even be int? with a struct constraint). That's because doing (T)(object) on an int first boxes the integer and then tries to unbox it. And a boxed int can only be unboxed to an int or int? (it's true for any value type, you can only unbox a value type T to a variable of type T or T? ). So this code being generic is close to useless, as it works with only one type.