Inheritance

[Scott Slater]

When you inherit one interface into another, I looks as if the instance variables *do not* get inherited. Is this the way it is supposed to work or am I missing something?

I guess they will need to be replaced with globals in this case as far as I can see.

[jcfuller]

When you inherit one interface into another, I looks as if the instance variables *do not* get inherited. Is this the way it is supposed to work or am I missing something?

I guess they will need to be replaced with globals in this case as far as I can see.

Your missing something.
It would help if you provided just a wee bit of code.

James

[Scott Slater]

Here is what I was experimenting with.

#Compile Exe
#Dim All

Class MyClass1
   Instance x As Long
   
   Interface MyInt1
      Inherit IUnknown
      Method DoubleX
         x *= 2
      End Method
      Property Get VarX() As Long
         Property = x
      End Property
      Property Set VarX(ByVal Invar As Long)
         x = Invar
      End Property
   End Interface
   
End Class

Class MyClass2

   Instance x As Long   ' If this line is *not* here, you get "Missing declaration X" compiler error...
                        ' If the line *is* there, then TrippleX does not work as expected...
   
   Interface MyInt2
      Inherit MyClass1, MyInt1
      Method TrippleX
         x *= 3
      End Method
   End Interface
   
End Class

Function PBMain () As Long

   Local MyObj As MyInt2
   
   MyObj = Class "MyClass2"
   
   MyObj.VarX = 5
   MyObj.TrippleX
   ? Format$(MyObj.VarX)   ' Result should be 15, but is not...

End Function

[José Roca]

Use this:

Class MyClass2

   Interface MyInt2
      Inherit MyClass1, MyInt1
      Method TrippleX
         ME.VarX = ME.Varx +3
      End Method
   End Interface
   
End Class

[Fred Harris]

...looks as if the instance variables *do not* get inherited.

Actually, there essentially aren't any such things as interface variables. Interfaces are actually memory blocks containing pointers to functions.

I actually myself haven't used the new PB compilers a great deal yet, but I stumbled over this issue at first too. In terms of other OOP languages inheritance of base class variables is supported to varying extents, for example in C++. However, the COM specification does not appear to allow for this, and PB likewise does not support it. Awhile back Kev Peel posted a work around for this which is pretty neat where properties instead of variables were used to transfer data between base and inheriting classes.

Here is the link to Kev's post...

http://www.powerbasic.com/support/pbforums/showthread.php?t=38392

[Scott Slater]

I see that there are work-arounds, but I guess my original question was if the "Instance" variables were inherited. It appears not in this case.