The forward declarations are tricky because ring_adjacency_iterator_generator adapts ring_incident_edge_iterator, which in turn has template parameters defined in terms of graph_traits<>.
After playing around a bit more I was able to use boost::adjacency_iterator_generator::type by making it a base class of ring_adjacency_iterator_generator. This ends up only saving a few keystrokes from the version that derives it directly from boost::adjacency_iterator, but it still feels like the right thing to do. I was also able to keep everything parameterized through graph_traits<>.
This example feels done. Thanks for your help.
On Wed, Jun 30, 2010 at 9:50 PM, Jeremiah Willcock
<jewillco@osl.iu.edu> wrote:
On Tue, 29 Jun 2010, W.P. McNeill wrote:
It looks like the adjacency_iterator created by adjacency_iterator_generator was being defined in terms of vertex_descriptor
and out_edge_iterator, which are in turn defined via graph_traits<>, which would cause this problem.
I got a little closer to an ideal solution by putting
typedef ring_adjacency_iterator adjacency_iterator;
in the graph class and forward-defining ring_adjacency_iterator, then later on in implicit.hpp deriving ring_adjacency_iterator
from boost::adjacency_iterator like so
class ring_adjacency_iterator:public boost::adjacency_iterator<
graph,
vertex_descriptor,
out_edge_iterator,
boost::use_default> {
public:
typedef boost::adjacency_iterator<
graph,
vertex_descriptor,
out_edge_iterator,
boost::use_default> parent_class;
ring_adjacency_iterator() {};
ring_adjacency_iterator(const out_edge_iterator& ei, const graph* g):
parent_class(ei, g) {};
};
I didn't have to typedef the adjacency_iterator to void in the graph definition, so this is a valid AdjacencyGraph model.
I like this better than writing my own iterator_adaptor because it uses boost::adjacency_iterator, though it feels a little hacky because
the body of ring_adjacency_iterator is mostly cut-and-pasted from adjacency_iterator.hpp.
I'd like to find a way to define the adjacency iterator with the generator using the statement
boost::adjacency_iterator_generator<graph, vertex_descriptor, out_edge_iterator>::type
but I haven't been able to do it. This generator statement relies on graph_traits<> properties vertex_descriptor and out_edge_iterator,
so has to come after the definition of implicit_ring::graph. But that means I have to have a forward declaration of the
adjacency_iterator, and I don't know how to forward-declare something I'm getting from boost::adjacency_iterator_generator<>::type.
It's still pretty good, but if this is going to be example code I'd like to make sure I'm doing it the best way possible.
-- Jeremiah Willcock
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