VB Nullables and Nothings - vb.net

Question

I researched C#'s default keyword equivalence in VB.NET and came across this question.
Then I got curious. Some background - I'm working with parsing an excel spreadsheet, where many columns can be null, and there is certainly a difference for me between an integer column being 0 and being null.
I wrote a little parse method:
Function Test(ByVal i As String) As Nullable(Of Integer)
Dim j As Integer
If Integer.TryParse(i, j) Then
Return j
Else
Return Nothing
End If
End Function
this seems to work correctly. But here, I can return an Integer if i want:
Function Test(ByVal i As String) As Nullable(Of Integer)
Return 2 'or Return Nothing
End Function
which I can in C# as well:
static void Main(string[] args)
{
int? j = Test("1");
}
public static int? Test(string i)
{
return 2; //or return null
}
In the code above, if I change j to an int, I'll get a compile-time conversion error, which makes total sense.
Now my question - in VB, if i attempt a similar approach:
Sub Main()
Dim j As Integer = Test("hello")
End Sub
Function Test(ByVal i As String) As Nullable(Of Integer)
Dim j As Integer
Return If(Integer.TryParse(i, j), j, Nothing)
End Function
or, in my test case where i is not an Integer it can be rewritten as:
Function Test(ByVal i As String) As Nullable(Of Integer)
Return DirectCast(Nothing, Integer)
End Function
because of the way Nothing works in VB.NET, this code compiles and runs without error -- j is set to Integer's default 0.
This feels so dirty to me. In this scenario you can somewhat alter the method's intentions without any warnings or errors. I'm just curious I suppose, is this an unintentional by-product of the way Nothing works in VB, or is this the intended purpose?

Answer 1

Your VB.Net code compiles because you're using late binding, which allows changing the type of a variable at runtime.
If you compile your code with OPTION STRICT ON, you'll get a compiler error like:
Option Strict On disallows implicit conversions from 'Integer?' to 'Integer'.

Answer 2

You can't assign NULL to a value type in VB.Net in which it instantiates that type with its default value. In your case you are not creating a NULL Integer, but an integer that holds the default value of 0.
Another good note: turn Option Strict On