Cloning (not human...)

[William Squires <wsquires at satx dot rr dot com>]

Another simple case...

Class ClonableBase
  Protected fMyProp As Integer

  Public Sub MyProp(Assigns i As Integer)
    fMyProp = i
  End Sub

  Public Function MyProp() As Integer
    Return fMyProp
  End Sub

  Public Sub ClonableBase()
    // This isn't strictly necessary as RB initializes variables to a 
0-equivalent, but I'm
    // retentive that way...
    fMyProp = 0
  End Sub

  Public Sub ClonableBase(o As ClonableBase)
    If (o <> nil) Then
      Me.MyProp = o.MyProp
    Else
      // Do something bad...
      Raise New NilObjectException
    End If
  End Sub

  Public Function Clone()
    Dim result As ClonableBase

    result = New ClonableBase(Me)
    Return result
  End Function
End Class

simple enough. Now make a subclass of ClonableBase:

Class ClonableSub : ClonableBase
  Protected fMyOtherProp As String

  Public Sub MyOtherProp(Assigns s As string)
    fMyOtherProp = Left(s, 1) // We only want 1 character
  End Sub

  Public Function MyOtherProp() As String
    Return fMyOtherProp
  End Sub

  Public Sub ClonableSub()
    Super.ClonableBase()
    fMyOtherProp = "Y"
  End Sub

  Public Sub ClonableSub(o As ClonableSub)
    Dim temp As ClonableBase

    temp = ClonableBase(o)
    Super.ClonableBase(temp)
    Me.MyOtherProp = o.MyOtherProp
  End Sub

  Public Function Clone()
    Dim result As ClonableSub

    result = New ClonableSub(Me)
    Return result
  End Sub
End Class

  This should - I hope - perform a 'deep copy'; a copy that produces a 
separate object whose properties match those of the cloned object 
(given either a ClonableBase or ClonableSub instance, and a call to its 
Clone() method).
  Question to RB OOP gurus: Is this the 'safe' way to do it, or will 
polymorphism throw me for a loop if I'm not careful, when calling it 
> from base class references (in an array, for example)? i.e. what will 
happen in the following code?

Dim theObjects(2) As ClonableBase
Dim theBaseObject As ClonableBase
Dim theSubObject As ClonableSub

theBaseObject = New ClonableBase()
theBaseObject.MyProp = 5 // just as a test
theSubObject = New ClonableSub()
theSubObject.MyOtherProp = "N" // 'nuther test
theObjects(0) = theBaseObject
theObjects(11) = theSubObject
....
// other code
....
theBaseObject = theObjects(1).Clone() // ??? what will I really get as 
the runtime type of 'theBaseObject'?
theSubObject = theObjects(1).Clone() // ??? is this legal?
theSubObject = ClonableSub(theObjects(1)).Clone // ??? is this legal?

William H Squires Jr
4400 Horizon Hill #4006
San Antonio, TX 78229
wsquires at satx dot rr dot com dot nospam <- remove the .nospam

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