Basics of conversion of Not nullable to Nullable type

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

What happens inside CLR ?

is value type is internally converted to refer开发者_开发百科ence type?

int i = 100;

and int ? i = 7?

is both are value type?

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An int? is the same as Nullable<int> which is a struct, i.e. a value type. There are no conversions to reference types here.

Here's the definition of Nullable from MSDN:

[SerializableAttribute]
public struct Nullable<T> where T : struct, new()

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int? i is just shorthand for System.Nullable <int> i. Both are indeed value types.

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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.