Question

How can I create a nullable numeric optional parameter in VB.NET?

Answer 1

EDIT: this should be possible in VB.NET 10 according to this blog post. If you’re using it then you could have:

Public Sub DoSomething(Optional ByVal someInteger As Integer? = Nothing)
    Console.WriteLine("Result: {0} - {1}", someInteger.HasValue, someInteger)
End Sub

' use it
DoSomething(Nothing)
DoSomething(20)

---

For versions other than VB.NET 10:

Your request is not possible. You should either use an optional parameter, or a nullable. This signature is invalid:

Public Sub DoSomething(Optional ByVal someInteger As Nullable(Of Integer) _
                        = Nothing)

You would get this compile error: “Optional parameters cannot have structure types.”

If you’re using a nullable then set it to Nothing if you don’t want to pass it a value. Choose between these options:

Public Sub DoSomething(ByVal someInteger As Nullable(Of Integer))
    Console.WriteLine("Result: {0} - {1}", someInteger.HasValue, someInteger)
End Sub

or

Public Sub DoSomething(Optional ByVal someInteger As Integer = 42)
    Console.WriteLine("Result: {0}", someInteger)
End Sub