Question

What is the basics of conversion of Not Nullable type to Nullable type?

What happens inside CLR ?

is value type is internally converted to reference type?

int i = 100;

and int ? i = 7?

is both are value type?

Answer 1

Run this to see that the int? is a value type:

class Program
{
    static int? nullInt;

    static void Main(string[] args)
    {
        nullInt = 2;
        Console.WriteLine(string.Format("{0} + 3 != {1}", nullInt, DoMath(nullInt , 3).ToString()));
        Console.WriteLine(string.Format("{0} * 3 = {1}" , nullInt , DoMultiply(nullInt , 3).ToString()));

        nullInt = null;
        Console.WriteLine(string.Format("{0} + 3 != {1}" , nullInt , DoMath(nullInt , 3).ToString()));
        Console.WriteLine(string.Format("{0} * 3 = {1}" , nullInt , DoMultiply(nullInt , 3).ToString()));

        Console.ReadLine();
    }

    static int? DoMath(int? x , int y)
    {
        if (x.HasValue)
        {
            return (++x) + y;
        }
        else
            return y;
    }

    static int DoMultiply(int? x , int y)
    {
        if (x.HasValue)
        {
            return (int)x * y;
        }
        else
            return 0;
    }
}

I have found these to be very interesting and makes for some clever uses.

What ? does is create a nullable reference to an otherwise non-nullable value type. It is like having a pointer that can be checked – HasValue (a boolean value)? Nice thing about the Nullable< T > is that the Value property does not need to be cast to it’s original type – that work is done for you inside the nullable struct.