[Gambas-devel] "Overriding" virtual classes

[Benoît Minisini]

Le 23/06/2014 19:15, Tobias Boege a écrit :
> Hi Benoit,
>
> for the Graph class in gb.data, I thought of having a non-creatable Graph
> class (we had that topic already in the past) which is the interface
> necessary for all concrete graph implementations. This class exposes a
> Graph.Edges property to a virtual .Graph.Edges class whose interface and
> default implementation are also specified.
>
> As I said earlier, I really want to have it this way because it enables the
> programmer to makde a decision on what graph data structure they need to use
> for their application and it also makes modelling non-Graph data as a Graph
> very easy. An example (which I want to implement as a Gambas example for
> Graphs) would be to have an Image object. Each pixel is a vertex and edges
> are implicitly defined between neighbouring pixels of the same colour. If
> you do a breadth-first search on this graph from a pixel, you are actually
> doing a flood-fill on the Image.
>
> This is where the virtual classes become an unbelievably handy thing: you
> don't have to create explicit vertex and edge *objects* from the Image but
> you can pipe the user requests through the virtual object's interface and
> operate on the backing data.
>
> If I now create a GraphMatrix class basing on adjacency matrices which
> Inherits Graph, I also need to point the Graph.Edges property to some
> concrete .GraphMatrix.Edges class which operates on the adjacency matrix.
>
> Is there a way to do this or can it be implemented? I could store the needed
> function pointers myself in a separate data structure and let the standard
> .Graph.Edges class reference those but this would not help Gambas programmers
> if they want to implement their Graph classes non-natively, right?
>
> So, I'm asking for a way to replace a virtual class with another virtual
> class in the inheritance process. [ Maybe you can make an exception in the
> inheritance checking routines since virtual classes are a thing of native
> components and native components writers should be supposed to know what
> they're doing? :-) ]
>
> Regards,
> Tobi
>

And if ".GraphMatrix.Edges" inherits ".Graph.Edges" too, doesn't it 
solve the problem?

-- 
Benoît Minisini