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?
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3 Answers
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.
