Nullable type is not a nullable type?

Question

I was doing some testing with nullable types, and it didn't work quite as I expected:

int? testInt = 0;
Type nullableType = typeof(int?);
Assert.AreEqual(nullableType, testInt.GetType()); // not the same type

My question is why does testInt.GetType() return int, and typeof(int?) return the true nullable type?

According to Enyra this should work. Guess what, it doesn't:

DateTime? test = new DateTime(434523452345);
Assert.IsTrue(test.GetType() == typeof(Nullable)); //FAIL 

DateTime? test = new DateTime(434523452345);
Assert.IsTrue(test.GetType() == typeof(Nullable<>)); //STILL FAIL

Answer 1

According to the MSDN :

Calling GetType on a Nullable type causes a boxing operation to be performed when the type is implicitly converted to Object. Therefore GetType always returns a Type object that represents the underlying type, not the Nullable type.

When you box a nullable object, only the underlying type is boxed.

Again, from MSDN :

Boxing a non-null nullable value type boxes the value type itself, not the System.Nullable that wraps the value type.

Answer 2

According to the MSDN

This is stupid! MS should fix this "bug".

Answer 3

I answered this question a few month ago on my own blog, you can read it here. A nullable type is always of type Nullable<>, so in your case it would be Nullable.

Answer 4

Further to Romain's correct answer, if you want to compare the "real" types (ie, without implicitly converting any nullable type to its underlying type) then you can create an extension method like so:

public static class MyExtensionMethods
{
    public static Type GetRealType<T>(this T source)
    {
        return typeof(T);
    }
}

And then try the following tests:

int? a = 0;
Console.WriteLine(a.GetRealType() == typeof(int?));         // True
Console.WriteLine(a.GetRealType() == typeof(int));          // False

int b = 0;
Console.WriteLine(b.GetRealType() == typeof(int));          // True
Console.WriteLine(b.GetRealType() == typeof(int?));         // False

DateTime? c = DateTime.Now;
Console.WriteLine(c.GetRealType() == typeof(DateTime?));    // True
Console.WriteLine(c.GetRealType() == typeof(DateTime));     // False

DateTime d = DateTime.Now;
Console.WriteLine(d.GetRealType() == typeof(DateTime));     // True
Console.WriteLine(d.GetRealType() == typeof(DateTime?));    // False