PowerPoint VBA - Passing Shapes by value seems to be happening by reference - vba

Question

For part of a VBA script I'm putting together I want to iterate through all the shapes on the current slide and insert another shape on top of each.
I have a first subroutine, GetShapes(), that gets all the shapes on the current slide and then passes them by value to a second subroutine, LabelShapes(), which adds the new shapes on top.
However, the new shapes seem to show up in the Shapes object that was passed. It seems like this should not be the case as it was passed by reference.
WARNING, the below will quickly lockup PowerPoint
Sub GetShapes()
Dim ss As Shapes
Set ss = Application.ActiveWindow.View.Slide.Shapes
Call LabelShapes(ss)
End Sub
Sub LabelShapes(ByVal ss As Shapes)
Dim s As Shape
For Each s In ss
Debug.Print s.Name
Application.ActiveWindow.View.Slide.Shapes.AddShape _
Type:=msoShapeRectangle, Left:=50, Top:=50, Width:=15, Height:=15
Next
End Sub
I imagine I can get around this by using a special naming convention for my new shapes and then filtering them out. Maybe there is a better way? But, really I would just like to understand why this isn't behaving the way I expect.

Answer 1

Not sure exactly what you're trying to do, but it's a common misunderstanding that passing object references ByVal would magically create a copy of the object.
Passing an object reference ByVal means you're passing a copy of the object pointer, as opposed to a reference to that very same object pointer.
In both cases, you're passing an object pointer that's pointing to the exact same object, so when you .AddShape, you're altering the very same shape collection you're in the middle of iterating.
Passing an object reference ByVal does NOT pass a copy of the object. If you want to pass a copy, you need to make a copy.
This might help clarify:
Public Sub DoSomething()
Dim obj As Object
Set obj = New Collection
TestByVal obj 'pass a copy of the object reference
Debug.Assert Not obj Is Nothing
TestByRef (obj) 'force a copy of the object reference (despite ByRef)
Debug.Assert Not obj Is Nothing
TestByRef obj 'pass a reference to the object pointer
Debug.Assert Not obj Is Nothing ' << assert will fail here
End Sub
Private Sub TestByVal(ByVal obj As Object)
Set obj = Nothing ' only affects the local copy
End Sub
Private Sub TestByRef(ByRef obj As Object)
Set obj = Nothing ' DANGER! call site will see this
End Sub

Answer 2

The solution is to use the ShapeRange object, which "represents a shape range, which is a set of shapes on a document."
Note from the Shapes documentation:
If you want to work with a subset of the shapes on a document — for example, to do something to only the AutoShapes on the document or to only the selected shapes — you must construct a ShapeRange collection that contains the shapes you want to work with.
Sub GetShapes()
Dim ss As ShapeRange
Set ss = Application.ActiveWindow.View.Slide.Shapes.Range
LabelShapes ss
End Sub
Sub LabelShapes(ByVal ss As ShapeRange)
Dim s As Shape
For Each s In ss
Debug.Print s.Name
Application.ActiveWindow.View.Slide.Shapes.AddShape _
Type:=msoShapeRectangle, Left:=50, Top:=50, Width:=15, Height:=15
Next
End Sub