Passing arguments to class initialise

[tiredofit]

We know it's not possible to pass arguments in a class in VBA and here is an attempt to overcome it:

https://stackoverflow.com/questions/15224113/pass-arguments-to-constructor-in-vba

However, instead of the above, can someone tell me what is wrong with this approach?

Declare a global variable and assign anything in the Class_Initialize to it. For example:

This is in Class1:

Option Explicit
 
Private Sub Class_Initialize()

    Dim abc As String

    abc = MySomeVariable.SomeVariable
    
End Sub

and this is in Class2:

Option Explicit

    Private pSomeVariable As String
    
Public Property Get SomeVariable() As String

    SomeVariable = pSomeVariable
    
End Property

Public Property Let SomeVariable(ByVal S As String)

    pSomeVariable = S
    
End Property

This is in a standard module:

Option Explicit

    Global MySomeVariable As Class2

Public Sub Test()
    
    Set MySomeVariable = New Class2
    
    MySomeVariable.SomeVariable = "Some string"
    
    Dim NewClass As Class1
    Set NewClass = New Class1
    
End Sub

 

[Domenic]

First, since you've declared your variable abc within the procedure Class_Initialize(), it has local scope. So when the procedure ends, the variable is not longer available. So you'll need to declared it at the module level, and then you'll need to create a Property Get procedure to retrieve the value.

So Class1 could be something like this...

Option Explicit

Dim m_abc As String

Public Property Get abc() As String
    abc = m_abc
End Property
 
Private Sub Class_Initialize()

    m_abc = MySomeVariable.SomeVariable
   
End Sub

And the code for your regular module like this...

Option Explicit

    Global MySomeVariable As Class2

Public Sub Test()
   
    Set MySomeVariable = New Class2
   
    MySomeVariable.SomeVariable = "Some string"
   
    Dim NewClass As Class1
    Set NewClass = New Class1
   
    MsgBox NewClass.abc, vbInformation
   
End Sub

However, with this approach, you're declaring a global variable, which in itself is not considered good programming practice. In addition, this approach seems somewhat convoluted, at least to me.

Personally, my preference would be the approach described in your link.

Hope this helps!

 

[tiredofit]

First, since you've declared your variable abc within the procedure Class_Initialize(), it has local scope. So when the procedure ends, the variable is not longer available. So you'll need to declared it at the module level, and then you'll need to create a Property Get procedure to retrieve the value.

So Class1 could be something like this...

Option Explicit

Dim m_abc As String

Public Property Get abc() As String
    abc = m_abc
End Property
 
Private Sub Class_Initialize()

    m_abc = MySomeVariable.SomeVariable
  
End Sub

And the code for your regular module like this...

Option Explicit

    Global MySomeVariable As Class2

Public Sub Test()
  
    Set MySomeVariable = New Class2
  
    MySomeVariable.SomeVariable = "Some string"
  
    Dim NewClass As Class1
    Set NewClass = New Class1
  
    MsgBox NewClass.abc, vbInformation
  
End Sub

However, with this approach, you're declaring a global variable, which in itself is not considered good programming practice. In addition, this approach seems somewhat convoluted, at least to me.

Personally, my preference would be the approach described in your link.

Hope this helps!

Thanks for correcting my code.

Re the point of declaring a public variable, I consider it only "half public" because it's declaring it via a class and not directly.

Would you agree this is less bad?

 

[Domenic]

Actually, the public or global variable is not being declared via a class. It's in fact being declared in a regular module. It just so happens that it's being declared as Class2.

It seems to me that the approach outlined in your link is more straight forward, and a lot easier to follow.

 

[tiredofit]

Actually, the public or global variable is not being declared via a class. It's in fact being declared in a regular module. It just so happens that it's being declared as Class2.

It seems to me that the approach outlined in your link is more straight forward, and a lot easier to follow.

Thanks for sharing your thoughts.

 

[Domenic]

You're very welcome, cheers!