Can I destroy a class instance even if there are still references?

Question

For debugging reasons I want to destroy a class instance which still as references. Is that possible? It doesn't have to be elegant or stable, because this'll never end up in production code.

To clarify:

Public Sub Main
    Dim o as MyClass
    Set o = New MyClass //o is created, one reference
    DestroyObject o     //Class_Terminate is called and the object destroyed
    //Further code, not using o
End Sub                 //Possible runtime error here (don't care)

Is that possible? One way would be to call IUnknown::Release to manually decrease the reference count, but how do I now how often I must call it?

Answer 1

As you know, the object itself will call Class_Terminate when it thinks its reference count has got to zero, so your suggestion of calling Release should do the trick - just keep calling Release until Release itself throws an error.

This page from Bruce McKinney's Hardcore Visual Basic suggests one possible way that it might sometimes be possible to get the reference count, but I don't think you need to get into that unless this scheme (of Releaseing till you can't Release no more) doesn't work.

"this'll never end up in production code" - careful with your assumptions, of course...

Answer 2

This is a very bad idea

Option Explicit

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As Long)

Private m_oRef As Class1

Private Sub Command1_Click()
    Dim o As Class1

    Set o = New Class1
    Set m_oRef = o
    DestroyObject o
    ' releasing m_oRef after this point will bring down the IDE '
End Sub

Private Sub DestroyObject(pArg As Object)
    Dim lRefCount       As Long
    Dim lIdx            As Long
    Dim pUnk            As IUnknown

    lIdx = ObjPtr(pArg) + &H20
    Call CopyMemory(lRefCount, ByVal lIdx, 4)
    For lIdx = 1 To lRefCount - 2
        Call CopyMemory(pUnk, pArg, 4)
        Set pUnk = Nothing
    Next
    Set pArg = Nothing
End Sub