ByVal or ByRef - Classes

The Class data type is a reference data type.
When you declare a variable with a Class data type it can be passed in using either ByRef or ByVal.
In VBA all reference data types are passed by reference although there is a subtle difference.
Although it is a Reference data type there is a subtle difference between passing ByRef vs ByVal 'myClassModule class module

'myClassModule
Private mstrPropertyName As String 

Property Get Property_Name() As String 
    Property_Name = mstrPropertyName 
End Property 

Property Let Property_Name(rData As String) 
    mstrPropertyName = rData 
End Property 

ByRef

Passing a class into a subroutine using ByRef allows the original class to the changed.

Public Sub Passing_Classes1() 
   Dim myClass As myClassModule 
   Set myClass = New myClassModule 
   
   myClass.Property_Name = "before" 
   Debug.Print myClass.Property_Name 

   Call ByReference(myClass) 
   Debug.Print myClass.Property_Name 
End Sub 

Public Function ByReference(ByRef theClass As myClassModule) 
    'this is the original
    'the class has been passed by reference so this change is made to the original class
    theClass.Property_Name = "after" 
   
    'the class has been passed by reference so this changes the original
    'the new class reference will be passed back
    'we can see this because the second Debug.Print displays "<blank>"
    Set theClass = New myClassModule 
End Function 

ByVal

Passing a class into a subroutine using ByVal allows the original class to the changed.

Public Sub Passing_Classes2() 
   Dim myClass As myClassModule 
   Set myClass = New myClassModule 
   
   myClass.Property_Name = "before" 
   Debug.Print myClass.Property_Name 
  
   Call ByValue(myClass) 
   Debug.Print myClass.Property_Name 

End Sub 

Public Function ByValue(ByVal theClass As myClassModule) 
    'the class has been passed by value so this change is made to the original class
    theClass.Property_Name = "after" 
   
    'the class has been passed by value so this changes just the local copy
    'any changes made to the class reference (ie new assignment) is contained within the subroutine
    'we can see this because the second Debug.Print display "after"
    Set theClass = New myClassModule 
End Function 

What is the difference between ByVal and ByRef in the context of Class data types ?
There is a difference between declaring a variable with a Variant data type as opposed to a Class data type.