Object behaviour of simple data types?

[Jan Tielens]

Hi all, In .NET all data types (Integer, Long, String, ...) are objects. But in my opinion, these data types don't really behave like normal objects. I noticed the following behaviour: Dim l As Long Msgbox(l = Nothing) 'Results in True Msgbox(l = 0) 'Results in True Even stranger behaviour: Dim l As Long l = 0 Msgbox(l = Nothing) 'Results in True I hoped that in .NET there would be a way to determine if a variable has been set or not. For example you have a class with a ID property (long), you would implement it like this: Public Class Test Private _id As Long Public Property ID As Long Get Return _id End Get Set(Value As Long) _id = Value End Set End Property End Class Suppose you would like to have functionality in this class, to save the data. In de Save sub, you would like to check if the ID property was set or not. I hoped you could do it like this: Public Sub Save If _id = Nothing Then 'Raise error to tell the ID property was not set. Else 'Save data End If End Save Was it wrong of me to expect such behaviour, or am I wrong somewhere? Thanks, Jan

[Richard Deeming]

First, you can't check for null references with If x = Nothing ... - you have to use If x **Is** Nothing ... Second, you can't perform reference comparison on value types. If x is a value type, If x Is Nothing ... will not compile. Try something like:

Public Class Test
Private _id As Long
Private _idSet As Boolean = False

Public Property ID As Long
    Get
        Return \_id
    End Get
    Set(ByVal Value As Long)
        \_id = Value
        \_idSet = True
    End Set
End Property

Public Sub Save()
    If \_idSet Then
        'Save Data
    Else
        'Throw exception
    End If
End Sub

End Class