Straightforward question: I have a few variables that are doubles. I would like to be able to store a "null" state in them, i.e. I need to be able to represent that the variable doesn't contain valid data. I'd really rather not associate a boolean "is valid" variable with every single double, that would be ugly and likely unnecessary.
First, I found out that one has to declare the variable differently to allow the concept of 'IsNothing' to be checked, so I do this:
dim someDouble as Double?
(Note the question mark). If I don't declare it like that, the error check gives me a "IsNot requires operands that have reference types" message.
Once declared, setting the variable to...
someDouble = Nothing
...seems to set it to zero, because it never runs the code in my if/else statement that checks whether someDouble IsNot Nothing... which is bad because the variable can legitimately store a 0 as a valid piece of data.
What am I missing here? Thanks!
EDIT: I left out that I was using properties in a class to Get and Set these values. It turns out I was doing things right except I left my Property's type as a Double instead of a Double? so it was casting back to zero instead of the Nothing value. Useful information still in the answers below, though!
you should go read on Nullable Structure on MSDN
this will explain how to use it
example:
Sub Main()
Dim someDouble As Double?
someDouble = Nothing
If someDouble.HasValue Then
Console.WriteLine(someDouble.ToString)
Else
Console.WriteLine("someDouble is nothing / null")
End If
Console.Read()
End Sub