[Lemon-user] Graphs need first and next?

[Kovács Péter]

Dear Ben,

This aspect of the graph concepts is a bit confused. Each graph class 
provides first and next functions for nodes and arcs/edges (a low level 
interface). However, they do not appear in the public documentation, 
probably to orient the users to use the higher level iterator 
interfaces. Almost all generic tools rely only on the iterators, but 
there are some exceptions, e.g. DFS. Therefore, it is important to 
require these functons in the concepts, as well. Actually, I dislike 
this "hidden" aspect of the concepts, I would prefer to correctly 
display these functions in the documentation.

If you would like to develop a new graph type, then I suggest you to 
follow the construction of the LEMON graph sturctures. E.g. in case of 
ListDigraph, there is a base class ListDigraphBase, which implements 
only the base interface (i.e. first, next functions) and neither 
iterator nor map classes. ListDigraph is just a typedef for 
DigraphExtender<ListDigraphBase>, where DigraphExtender is a special 
class that extends the interface of the template parameter to fully 
conform to the Digraph concept.

I suggest you to have a look at list_graph.h and bits/graph_extender.h 
for better understanding.

Best regards,
Peter


> Hello,
>
> I have been implementing a specialized graph structure and have
> implemented the interface as described in the documentation:
> http://lemon.cs.elte.hu/pub/doc/latest/a00099.html
> There first and next are not listed.
>
> However lemon/dfs.h makes use of them and  lemon/concepts/digraph.h
> lists prototypes for those functions. Am I supposed to implement them or
> am I missing something?
>
> Regards,
> Ben Strasser
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