[boost] [Boost.Graph] specifying PropertyGraphConcept requirements

From: Brook Milligan (brook_at_[hidden])
Date: 2007-02-22 13:41:37

I am trying to specify the requirement that types cover the
PropertyGraphConcept of the BGL.  The following code illustrates a
simple test case.

     #include <boost/graph/adjacency_list.hpp>

     struct VertexProperties
     {
       typedef VertexProperties kind;
       int distance;
     };

     struct EdgeProperties
     {
       typedef EdgeProperties kind;
       int weight;
     };

     typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS,
                                   VertexProperties, EdgeProperties> graph_type;

     int
     main()
     {
       boost::function_requires< boost::PropertyGraphConcept<graph_type,
         int, int VertexProperties::*> >();

       return 0;
     }

However, with Boost v1.33.1, the concept check yields the following
error:

     /usr/pkg/include/boost/property_map.hpp:158: error: assignment of read-only 
        data-member `
        boost::ReadablePropertyMapConcept<boost::bundle_property_map<const 
        graph_type, size_t, VertexProperties, const int>, int>::val'

The location of that error is associated with the indicated line
clipped out of property_map.hpp:

     // property_map.hpp

     template <class PMap, class Key>
     struct ReadablePropertyMapConcept
     {
       typedef typename property_traits<PMap>::key_type key_type;
       typedef typename property_traits<PMap>::reference reference;
       typedef typename property_traits<PMap>::category Category;
       typedef boost::readable_property_map_tag ReadableTag;
       void constraints() {
         function_requires< ConvertibleConcept<Category, ReadableTag> >();

         val = get(pmap, k); // <== read-only assignment error
       }
       PMap pmap;
       Key k;
       typename property_traits<PMap>::value_type val;
     };

Perhaps the template arguments in the concept checking are wrong; I
have found the documentation unclear on how to really use these.  Any
help on how to make this work correctly is greatly appreciated.

Thanks alot.

Cheers,
Brook