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How to hide base class member variable in derived class (w/o shadows)?I have a base class that has some member variables I do not want to be inherited or visible by any instance of that derived class. Class cBase Public mVariable As String ... Class cDerived Inherits cBase Hide mVariable ' <<< Private Shadows mVariable As ... is not working The problem if I use Private Shadows in the derived class is that an instance will still show the variable in the base class: Dim lDummy As New cDerived lDummy.mVariable will be mVariable of cBase. I tried Protected in cBase but then I cannot see mVariable in other derived classes anymore. I realize that there is no data encapsulation in my example but there is a (legacy) reason for that. I would have the same problem if I were to use an accessor or Property. Is there any mechanism in VB.NET that will allow me to completely hide a member variable of the base class in a particular derived class? Thanks, Joe Joe Duchtel wrote:
> Hello - You inherit everything from the base class.> > I have a base class that has some member variables I do not want to be > inherited or visible by any instance of that derived class. Show quoteHide quote > Class cBase Really? This works:> Public mVariable As String > ... > > Class cDerived > Inherits cBase > > Hide mVariable ' <<< Private Shadows mVariable As ... is not > working > > The problem if I use Private Shadows in the derived class is that an > instance will still show the variable in the base class: > Dim lDummy As New cDerived > lDummy.mVariable will be mVariable of cBase. > I tried Protected in cBase but then I cannot see mVariable in other > derived classes anymore. Class cBase Protected mVariable As String End Class Class cDerived Inherits cBase Sub sdfsdf() mVariable = "sdf" 'works End Sub End Class > I realize that there is no data encapsulation in my example but there Not that I know of.> is a (legacy) reason for that. I would have the same problem if I > were to use an accessor or Property. > > Is there any mechanism in VB.NET that will allow me to completely hide > a member variable of the base class in a particular derived class? Armin
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On Jun 17, 5:41 pm, "Armin Zingler" <az.nos***@freenet.de> wrote: Hello -> Joe Duchtel wrote: > > Hello - > > > I have a base class that has some member variables I do not want to be > > inherited or visible by any instance of that derived class. > > You inherit everything from the base class. > > > > > > > Class cBase > > Public mVariable As String > > ... > > > Class cDerived > > Inherits cBase > > > Hide mVariable ' <<< Private Shadows mVariable As ... is not > > working > > > The problem if I use Private Shadows in the derived class is that an > > instance will still show the variable in the base class: > > Dim lDummy As New cDerived > > lDummy.mVariable will be mVariable of cBase. > > I tried Protected in cBase but then I cannot see mVariable in other > > derived classes anymore. > > Really? This works: > > Class cBase > Protected mVariable As String > End Class > > Class cDerived > Inherits cBase > Sub sdfsdf() > mVariable = "sdf" 'works > End Sub > End Class > > > I realize that there is no data encapsulation in my example but there > > is a (legacy) reason for that. I would have the same problem if I > > were to use an accessor or Property. > > > Is there any mechanism in VB.NET that will allow me to completely hide > > a member variable of the base class in a particular derived class? > > Not that I know of. > > Armin- Hide quoted text - > > - Show quoted text - I understand inheritance and how Protected works but I was looking for something outside of the derived class. Here is a full example of what I'm trying to do written out ... Module Test Public Class cBase Public mA As String = String.Empty Public mB As String = String.Empty End Class Public Class cDerivedA Inherits cBase Private Shadows mA As String = String.Empty End Class Public Class cDerivedB Inherits cBase End Class Sub Main() Dim lDerivedAInstance As New cDerivedA lDerivedAInstance.mA = "THIS SHOULD NOT WORK!" lDerivedAInstance.mB = "OK" Dim lDerivedBInstance As New cDerivedB lDerivedAInstance.mA = "OK" lDerivedAInstance.mA = "OK" End Sub End Module The lDerivedAInstance.mA = "..." only works because it accesses the instance of mA in cBase. If I protect that in cBase, I cannot access it through an instance of cDerivedB anymore. Thanks! Joe Joe Duchtel wrote:
> I understand inheritance and how Protected works but I was looking for I know, but you wrote> something outside of the derived class. >> I tried Protected in cBase but then I cannot see mVariable in other I wasn't able to repro this problem. Anyway, it's not possible what you're >> derived classes anymore. trying to do. But why do you want to do it? If every car (base class) has wheels and an engine, a BMW (derived class) doesn't have an engine only. Armin
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On Jun 17, 9:13 pm, "Armin Zingler" <az.nos***@freenet.de> wrote: Hello -> Joe Duchtel wrote: > > I understand inheritance and how Protected works but I was looking for > > something outside of the derived class. > > I know, but you wrote > > >> I tried Protected in cBase but then I cannot see mVariable in other > >> derived classes anymore. > > I wasn't able to repro this problem. Anyway, it's not possible what you're > trying to do. > > But why do you want to do it? If every car (base class) has wheels and an > engine, a BMW (derived class) doesn't have an engine only. > > Armin Sorry ... I guess I was not very clear in that first paragraph. I figured that this is not really supported. I understand that this idea defies OOP to some extent but I have to deal with some legacy code that I cannot break to make it work in a better way. Thanks! Joe Perhaps by using a real interface ? Not sure if it would break your existing
code ? At some point you have either to accept glitches in your legacy design or redesign to fit good practices... -- Patrice "Joe Duchtel" <duch***@gmail.com> a écrit dans le message de groupe de 9cf40722-31af-4968-8d96-814ce089f***@k2g2000yql.googlegroups.com...discussion : Show quoteHide quote > On Jun 17, 5:41 pm, "Armin Zingler" <az.nos***@freenet.de> wrote: >> Joe Duchtel wrote: >> > Hello - >> >> > I have a base class that has some member variables I do not want to be >> > inherited or visible by any instance of that derived class. >> >> You inherit everything from the base class. >> >> >> >> >> >> > Class cBase >> > Public mVariable As String >> > ... >> >> > Class cDerived >> > Inherits cBase >> >> > Hide mVariable ' <<< Private Shadows mVariable As ... is not >> > working >> >> > The problem if I use Private Shadows in the derived class is that an >> > instance will still show the variable in the base class: >> > Dim lDummy As New cDerived >> > lDummy.mVariable will be mVariable of cBase. >> > I tried Protected in cBase but then I cannot see mVariable in other >> > derived classes anymore. >> >> Really? This works: >> >> Class cBase >> Protected mVariable As String >> End Class >> >> Class cDerived >> Inherits cBase >> Sub sdfsdf() >> mVariable = "sdf" 'works >> End Sub >> End Class >> >> > I realize that there is no data encapsulation in my example but there >> > is a (legacy) reason for that. I would have the same problem if I >> > were to use an accessor or Property. >> >> > Is there any mechanism in VB.NET that will allow me to completely hide >> > a member variable of the base class in a particular derived class? >> >> Not that I know of. >> >> Armin- Hide quoted text - >> >> - Show quoted text - > > Hello - > > I understand inheritance and how Protected works but I was looking for > something outside of the derived class. Here is a full example of > what I'm trying to do written out ... > > Module Test > Public Class cBase > Public mA As String = String.Empty > Public mB As String = String.Empty > End Class > > Public Class cDerivedA > Inherits cBase > > Private Shadows mA As String = String.Empty > End Class > > Public Class cDerivedB > Inherits cBase > End Class > > Sub Main() > Dim lDerivedAInstance As New cDerivedA > lDerivedAInstance.mA = "THIS SHOULD NOT WORK!" > lDerivedAInstance.mB = "OK" > > Dim lDerivedBInstance As New cDerivedB > lDerivedAInstance.mA = "OK" > lDerivedAInstance.mA = "OK" > End Sub > End Module > > The lDerivedAInstance.mA = "..." only works because it accesses the > instance of mA in cBase. If I protect that in cBase, I cannot access > it through an instance of cDerivedB anymore. > > Thanks! > Joe More specifically :
Public Class cBase Public mA As String = String.Empty Public mB As String = String.Empty End Class Interface ICDerivedA Property mb() As String End Interface Public Class cDerivedA Inherits cBase Implements ICDerivedA Private Shadows mA As String = String.Empty Public Shadows Property mB() As String Implements ICDerivedA.mb Get Return MyBase.mB End Get Set(ByVal value As String) MyBase.mB = value End Set End Property End Class Public Class cDerivedB Inherits cBase End Class Sub Main() Dim lDerivedAInstance As ICDerivedA = New cDerivedA lDerivedAInstance.mA = "THIS SHOULD NOT WORK!" ' DOESN'T COMPILE lDerivedAInstance.mb = "OK" Dim lDerivedBInstance As New cDerivedB lDerivedBInstance.mA = "OK" lDerivedBInstance.mA = "OK" End Sub But I'm not sure if it wouldn't break your existing code. Also you could reverse the inheritance relation (as in your sample cBase handles all what cDerivedA handles not the other way round) but once again we don't know how it would impact your existing code... Or make them properties (is this possible) and throw an exception to at least prevent what you don't want at runtime or even add an "obsolete" attribute to see if it prevents compiling. At some point you'll have to weight living with those workarounds agaisnt changing the design (this is not VB.NET legacy code ?)... -- Patrice "Patrice" <http://www.chez.com/scribe/> a écrit dans le message de groupe de discussion : u$SWYzA8JHA.4***@TK2MSFTNGP02.phx.gbl...Show quoteHide quote > Perhaps by using a real interface ? Not sure if it would break your > existing code ? > > At some point you have either to accept glitches in your legacy design or > redesign to fit good practices... > > -- > Patrice > > > "Joe Duchtel" <duch***@gmail.com> a écrit dans le message de groupe de > discussion : > 9cf40722-31af-4968-8d96-814ce089f***@k2g2000yql.googlegroups.com... >> On Jun 17, 5:41 pm, "Armin Zingler" <az.nos***@freenet.de> wrote: >>> Joe Duchtel wrote: >>> > Hello - >>> >>> > I have a base class that has some member variables I do not want to be >>> > inherited or visible by any instance of that derived class. >>> >>> You inherit everything from the base class. >>> >>> >>> >>> >>> >>> > Class cBase >>> > Public mVariable As String >>> > ... >>> >>> > Class cDerived >>> > Inherits cBase >>> >>> > Hide mVariable ' <<< Private Shadows mVariable As ... is not >>> > working >>> >>> > The problem if I use Private Shadows in the derived class is that an >>> > instance will still show the variable in the base class: >>> > Dim lDummy As New cDerived >>> > lDummy.mVariable will be mVariable of cBase. >>> > I tried Protected in cBase but then I cannot see mVariable in other >>> > derived classes anymore. >>> >>> Really? This works: >>> >>> Class cBase >>> Protected mVariable As String >>> End Class >>> >>> Class cDerived >>> Inherits cBase >>> Sub sdfsdf() >>> mVariable = "sdf" 'works >>> End Sub >>> End Class >>> >>> > I realize that there is no data encapsulation in my example but there >>> > is a (legacy) reason for that. I would have the same problem if I >>> > were to use an accessor or Property. >>> >>> > Is there any mechanism in VB.NET that will allow me to completely hide >>> > a member variable of the base class in a particular derived class? >>> >>> Not that I know of. >>> >>> Armin- Hide quoted text - >>> >>> - Show quoted text - >> >> Hello - >> >> I understand inheritance and how Protected works but I was looking for >> something outside of the derived class. Here is a full example of >> what I'm trying to do written out ... >> >> Module Test >> Public Class cBase >> Public mA As String = String.Empty >> Public mB As String = String.Empty >> End Class >> >> Public Class cDerivedA >> Inherits cBase >> >> Private Shadows mA As String = String.Empty >> End Class >> >> Public Class cDerivedB >> Inherits cBase >> End Class >> >> Sub Main() >> Dim lDerivedAInstance As New cDerivedA >> lDerivedAInstance.mA = "THIS SHOULD NOT WORK!" >> lDerivedAInstance.mB = "OK" >> >> Dim lDerivedBInstance As New cDerivedB >> lDerivedAInstance.mA = "OK" >> lDerivedAInstance.mA = "OK" >> End Sub >> End Module >> >> The lDerivedAInstance.mA = "..." only works because it accesses the >> instance of mA in cBase. If I protect that in cBase, I cannot access >> it through an instance of cDerivedB anymore. >> >> Thanks! >> Joe > >
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On Jun 18, 11:55 am, "Patrice" <http://www.chez.com/scribe/> wrote: Hello -> More specifically : > > Public Class cBase > Public mA As String = String.Empty > Public mB As String = String.Empty > End Class > Interface ICDerivedA > Property mb() As String > End Interface > > Public Class cDerivedA > Inherits cBase > Implements ICDerivedA > Private Shadows mA As String = String.Empty > Public Shadows Property mB() As String Implements ICDerivedA.mb > Get > Return MyBase.mB > End Get > Set(ByVal value As String) > MyBase.mB = value > End Set > End Property > End Class > > Public Class cDerivedB > Inherits cBase > End Class > > Sub Main() > Dim lDerivedAInstance As ICDerivedA = New cDerivedA > lDerivedAInstance.mA = "THIS SHOULD NOT WORK!" ' DOESN'T COMPILE > lDerivedAInstance.mb = "OK" > > Dim lDerivedBInstance As New cDerivedB > lDerivedBInstance.mA = "OK" > lDerivedBInstance.mA = "OK" > End Sub > > But I'm not sure if it wouldn't break your existing code. Also you could > reverse the inheritance relation (as in your sample cBase handles all what > cDerivedA handles not the other way round) but once again we don't know how > it would impact your existing code... > > Or make them properties (is this possible) and throw an exception to at > least prevent what you don't want at runtime or even add an "obsolete" > attribute to see if it prevents compiling. > > At some point you'll have to weight living with those workarounds agaisnt > changing the design (this is not VB.NET legacy code ?)... > > -- > Patrice > > "Patrice" <http://www.chez.com/scribe/> a écrit dans le message de groupe de > discussion : u$SWYzA8JHA.4***@TK2MSFTNGP02.phx.gbl... > > > > > Perhaps by using a real interface ? Not sure if it would break your > > existing code ? > > > At some point you have either to accept glitches in your legacy design or > > redesign to fit good practices... > > > -- > > Patrice > > > "Joe Duchtel" <duch***@gmail.com> a écrit dans le message de groupe de > > discussion : > > 9cf40722-31af-4968-8d96-814ce089f***@k2g2000yql.googlegroups.com... > >> On Jun 17, 5:41 pm, "Armin Zingler" <az.nos***@freenet.de> wrote: > >>> Joe Duchtel wrote: > >>> > Hello - > > >>> > I have a base class that has some member variables I do not want to be > >>> > inherited or visible by any instance of that derived class. > > >>> You inherit everything from the base class. > > >>> > Class cBase > >>> > Public mVariable As String > >>> > ... > > >>> > Class cDerived > >>> > Inherits cBase > > >>> > Hide mVariable ' <<< Private Shadows mVariable As ... is not > >>> > working > > >>> > The problem if I use Private Shadows in the derived class is that an > >>> > instance will still show the variable in the base class: > >>> > Dim lDummy As New cDerived > >>> > lDummy.mVariable will be mVariable of cBase. > >>> > I tried Protected in cBase but then I cannot see mVariable in other > >>> > derived classes anymore. > > >>> Really? This works: > > >>> Class cBase > >>> Protected mVariable As String > >>> End Class > > >>> Class cDerived > >>> Inherits cBase > >>> Sub sdfsdf() > >>> mVariable = "sdf" 'works > >>> End Sub > >>> End Class > > >>> > I realize that there is no data encapsulation in my example but there > >>> > is a (legacy) reason for that. I would have the same problem if I > >>> > were to use an accessor or Property. > > >>> > Is there any mechanism in VB.NET that will allow me to completely hide > >>> > a member variable of the base class in a particular derived class? > > >>> Not that I know of. > > >>> Armin- Hide quoted text - > > >>> - Show quoted text - > > >> Hello - > > >> I understand inheritance and how Protected works but I was looking for > >> something outside of the derived class. Here is a full example of > >> what I'm trying to do written out ... > > >> Module Test > >> Public Class cBase > >> Public mA As String = String.Empty > >> Public mB As String = String.Empty > >> End Class > > >> Public Class cDerivedA > >> Inherits cBase > > >> Private Shadows mA As String = String.Empty > >> End Class > > >> Public Class cDerivedB > >> Inherits cBase > >> End Class > > >> Sub Main() > >> Dim lDerivedAInstance As New cDerivedA > >> lDerivedAInstance.mA = "THIS SHOULD NOT WORK!" > >> lDerivedAInstance.mB = "OK" > > >> Dim lDerivedBInstance As New cDerivedB > >> lDerivedAInstance.mA = "OK" > >> lDerivedAInstance.mA = "OK" > >> End Sub > >> End Module > > >> The lDerivedAInstance.mA = "..." only works because it accesses the > >> instance of mA in cBase. If I protect that in cBase, I cannot access > >> it through an instance of cDerivedB anymore. > > >> Thanks! > >> Joe- Hide quoted text - > > - Show quoted text - This is actually pretty slick. I have never used the Interface before but it works beautifully. Now I'll just have to figure out how to make it work without breaking some of the legacy code. I agree that at some point you just have to move forward but the impact is huge ... Thank a lot! Joe You are welcome and good luck. Just double check that the code you'll would
add to add these kind of workarounds won't make things even worst to update in the future. If you can change mA to a property, my personal prefererence would be likely to add an Obsolete attribute in the derived class (not tried bu I don't see why it wouldn't work) and always check that I have the same number of warnings in my code... Basically the code is unchanged and you have this under control before doing a more drastic move... -- Patrice 
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