Question

Is there a generic way to clone objects in VBA? So that i could copy x to y instead of copying just the pointer?

  Dim x As New Class1   Dim y As Class1    x.Color = 1   x.Height = 1    Set y = x   y.Color = 2    Debug.Print 'x.Color=' & x.Color & ', x.Height=' & x.Height 

By generic i mean something like Set y = CloneObject(x) rather than having to create my own method for the class copying its properties one by one.

Answer 1

OK, here’s the beginning of something that illustrates it:

Create a class, call it, oh, ‘Class1’:

Option Explicit  Public prop1 As Long Private DontCloneThis As Variant  Public Property Get PrivateThing()     PrivateThing = DontCloneThis End Property  Public Property Let PrivateThing(value)     DontCloneThis = value End Property 

Now we need to give it a Clone function. In another module, try this:

Option Explicit

Public Sub makeCloneable()  Dim idx As Long Dim line As String Dim words As Variant Dim cloneproc As String  ' start building the text of our new function     cloneproc = 'Public Function Clone() As Class1' & vbCrLf     cloneproc = cloneproc & 'Set Clone = New Class1' & vbCrLf      ' get the code for the class and start examining it         With ThisWorkbook.VBProject.VBComponents('Class1').CodeModule          For idx = 1 To .CountOfLines              line = Trim(.lines(idx, 1)) ' get the next line             If Len(line) > 0 Then                 line = Replace(line, '(', ' ') ' to make words clearly delimited by spaces                 words = Split(line, ' ') ' so we get split on a space                 If words(0) = 'Public' Then ' can't set things declared Private                     ' several combinations of words possible                     If words(1) = 'Property' And words(2) = 'Get' Then                         cloneproc = cloneproc & 'Clone.' & words(3) & '=' & words(3) & vbCrLf                     ElseIf words(1) = 'Property' And words(2) = 'Set' Then                         cloneproc = cloneproc & 'Set Clone.' & words(3) & '=' & words(3) & vbCrLf                     ElseIf words(1) <> 'Sub' And words(1) <> 'Function' And words(1) <> 'Property' Then                         cloneproc = cloneproc & 'Clone.' & words(1) & '=' & words(1) & vbCrLf                     End If                 End If             End If         Next          cloneproc = cloneproc & 'End Function'          ' put the code into the class         .AddFromString cloneproc      End With  End Sub 

Run that, and the following gets added into Class1

Public Function Clone() As Class1 Set Clone = New Class1 Clone.prop1 = prop1 Clone.PrivateThing = PrivateThing End Function 

…which looks like a start. Lots of things I’d clean up (and probably will – this turned out to be fun). A nice Regular Expression to find gettable/lettable/settable attributes, refactoring into several small functions, code to remove old ‘Clone’ functions (and put the new one at the end), something a bit more Stringbuilder-ish to DRY (Don’t Repeat Yourself) up the concatenations, stuff like that.