Class on a class

[tiredofit]

I have a variable, Var1, which is of type Class2.

Standard Module:

Option Explicit


Sub Test()

    Dim a As Class1
    Set a = New Class1
    
    a.Var1.Var2 = 7678

End Sub

Class1

Option Explicit


    Private pVar1 As New Class2


Public Property Get Var1() As Class2


    Set Var1 = pVar1
    
End Property


Public Property Set Var1(ByVal vNewValue As Class2)


    Set pVar1 = vNewValue
    
End Property


Private Sub Class_Initialize()


    Var1.Var2 = 336
    
End Sub

Class2

Option Explicit


    Private pVar2 As String


Public Property Get Var2() As String


    Var2 = pVar2
    
End Property


Public Property Let Var2(ByVal vNewValue As String)


    pVar2 = vNewValue
    
End Property

The code above works.

We use Let for "normal" variables and Set for object variables.

What I don't understand is this line:

Private Sub Class_Initialize()


    Var1.Var2 = 336
    
End Sub

Since Var1 is of type Var2, I expected to have to write:

Private Sub Class_Initialize()


    SET Var1.Var2 = 336
    
End Sub

Why don't I need to SET keyword here?

Is it because of this line at the top of Class1?

    Private pVar1 As New Class2

Thanks

 

[StephenCrump]

Var1.Var2 = 336

Why don't I need to SET keyword here?

.. because you're setting the Var2 property (which is a string) of the existing Var1 object.

Just by the way, it's better to avoid auto-instancing, e.g. Private pVar1 As New Class2
See Chip Pearson's comments, for example:
http://www.cpearson.com/excel/classes.aspx
http://www.cpearson.com/excel/declaringvariables.aspx

Instead:

'In Class1
Private pVar1 As Class2
Private Sub Class_Initialize()

    Set pVar1 = New Class2
    pVar1.Var2 = "336"    'for your testing purposes
    
End Sub

 

[tiredofit]

Thanks

 

[StephenCrump]

Thanks for the PM ...

No, I wouldn't call this inheritance .. you've just defined Class1 as having a property that is a Class2 object. That doesn't mean that Class2 will inherit any other properties or methods of Class1 that you may choose to define.

VBA doesn't support direct inheritance, but you can use class interfaces, e.g. http://www.cpearson.com/excel/Implements.aspx

 

[tiredofit]

Thanks again.