[Boost-users] [graph] vertex property Graph type cyclic definition problem. forward declaration not possible.

12 Oct 2011

      Hi,

i would like to use the bundled properties feature of the boost graph
library to specify the vertex properties of my graph. The problem is
that i would like to have some graph type dependent descriptor type map
defined within these vertex properties.

Here is the example:
// begin code
#include <iostream>
#include <boost/graph/adjacency_list.hpp>

struct vertex_properties {
	vertex_properties () : color (-1) {}
	int color;
	std::list <int>	free_colors;
std::map<int,link_graph_traits::edge_descriptor>	used_colors; // this is
a cycle def problem
};
struct edge_properties {
	edge_properties () : color (-1) {}
	int color;
};

struct graph_properties {
	int delta;
};

typedef boost::adjacency_list < boost::listS,
			boost::vecS,
			boost::bidirectionalS,
			vertex_properties,// this is a cycle problem
			edge_properties,
			graph_properties>
link_graph;

typedef boost::graph_traits <link_graph> 
link_graph_traits;

int main(int argc, char** argv) {

	link_graph g;
    return 0;
}
// end code

This example won't compile because the 'struct vertex_properties'
contains a variable declaration of a std::map which contains the type
('link_graph_traits::edge_descriptor') as a template parameter that is
not defined yet. 

I tried to forward declare the 'struct vertex_properties;' and move the
definition of 'struct vertex_properties {...};' behind the graph type
definition but then the compiler complained about.

The forward declaration code, that does not compile, too follows:
// begin code
#include <iostream>
#include <boost/graph/adjacency_list.hpp>

struct vertex_properties; 

struct edge_properties {
	edge_properties () : color (-1) {}
	int color;
};

struct graph_properties {
	int delta;
};

typedef boost::adjacency_list < boost::listS,
				boost::vecS,
				boost::bidirectionalS,
				vertex_properties,
				edge_properties,
				graph_properties>
link_graph;

typedef boost::graph_traits <link_graph> 
link_graph_traits;

struct vertex_properties {
	vertex_properties () : color (-1) {}
	int color;
	std::list <int>	free_colors;
std::map <int, link_graph_traits::edge_descriptor>
used_colors;
};

int main(int argc, char** argv) {

	link_graph g;
    return 0;
}
// end code

I do not want to use (void*) and std::reinterpret_cast to work around
this problem. I hope that you can help me with a technique not using
casts.

I assume that there may be a possibility to first declare the graph type
without the vertex_properties struct and then 'adding' the
vertex_propterties struct after defining the graph.

best regards
Christoph