Re: BGL: implementing internal properties - howto ?

From: artwisz_at_[hidden]
Date: 2001-03-25 07:00:10

Hello once again,

> artwis> One shortcut I thought of was simply to derive my graph 
class from a 
> artwis> specialized adjacency_list and overload all operations 
tunneling most 
> artwis> of them to the base class, but still I need to partially 
specialize 
> artwis> the property_map, so that I can write
> artwis> 
> artwis>    property_map<MyGraphType, vertex_bits_t>::type bits
> artwis>       = get(vertex_bits, g);
> artwis> 
> artwis> instead of
> artwis> 
> artwis>    property_map<MyGraphType::Base, vertex_bits_t>::type bits
> artwis>       = get(vertex_bits, g);
> artwis> 

I think I'm getting closer, I wrote my property selector:

struct bit_matrix_tag { };

template<class BitRep>
class bit_matrix : public boost::adjacency_list<...,
                                                boost::property<
                                                    vertex_bits_t, 
                                                    BitRep> > 
 { ... };

struct bit_matrix_vertex_property_selector
   {
   template<class Graph, class Property, class PropertyTag>
   struct bind
      {
      typedef typename Graph::Base BaseGraph;
      typedef typename BaseGraph::graph_tag base_tag;
      typedef typename
              boost::vertex_property_selector<base_tag>::type 
                                                       BaseSelector;
      typedef typename Property::tag_type Tag;
      typedef typename 
              BaseSelector::template bind<BaseGraph, Property, Tag> 
                                                       Bind;
      typedef typename Bind::type type;
      typedef typename Bind::const_type const_type;
      };
   };

template<>
struct boost::vertex_property_selector<bit_matrix_tag>
   {
   typedef bit_matrix_vertex_property_selector type;
   };

and it seems to bo OK. One thing that bothers me: why is there the 
PropertyTag template param if I can deduce the PropertyTag from 
Property ? I assume Property is an instance of struct property. 
Perhaps it is possible to have a property that is not specialized 
from struct property ?
Another thing I would like to do is to have some properties handled 
by the base class and other by my derived class. I guess I would need 
another layer of selectors... but this is fine at the moment.
BTW I can sniff a kind of meta-idiom in all that selectors stuff that 
is itself worth a doc page.
Regards,

Art