Question

Basically I want the following generic function:

public string StringOrNull<T> (T value)
{
    if (value != null)
    {
       return value.ToString();
    }
    return null;
}

I know I could use a constraint such as where T: class, but T can be a primitive type, Nullable<>, or a class. Is there a generic way to do this?

Edit

Turns out I jumped the gun. This actually works just fine as this sample shows:

    class Program
    {
        static void Main(string[] args)
        {
            int i = 7;
            Nullable<int> n_i = 7;
            Nullable<int> n_i_asNull = null;
            String foo = "foo";
            String bar = null;


            Console.WriteLine(StringOrNull(i));
            Console.WriteLine(StringOrNull(n_i));
            Console.WriteLine(StringOrNull(n_i_asNull));
            Console.WriteLine(StringOrNull(foo));
            Console.WriteLine(StringOrNull(bar));


        }

        static private string StringOrNull<T>(T value)
        {
            if (value != null)
            {
                return value.ToString();
            }
            return null;
        }
    }

Answer 1

Here’s a fun one:

public static class ExtensionFunctions{
    public static string ToStringOrNull( this object target ) {
        return target != null ? target.ToString() : null;
    }
}

The cool part? This will work:

( (string) null ).ToStringOrNull();

So will this:

 5.ToStringOrNull();

Extension functions are pretty awesome… they even work on null objects!

If you pass a primitive type, it will automatically be boxed, so you don’t need to worry about the null comparison. Since boxing occurs automatically, you can even explicitly compare an int to null without an error, but the result will always be false (and you’ll probably get a compiler warning telling you so).