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 

This doesn’t work either:

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 

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

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.