Hi Jeremiah, In many cases, an edge_descriptor is a pair<vertex_descriptor, vertex_descriptor>. If the container of adjacent vertices is an unsorted vector or list, then it requires searching that list. An out_edge_iterator on the other hand is likely an iterator pointing directly to the edge in question. Yes, an edge_descriptor could contain an edge_iterator, but that increases the size and complexity of an edge_descriptor unnecessarily. Cheers, Shaun On Thu, 2010-12-16 at 22:11 -0800, Jeremiah Willcock wrote:
On Thu, 16 Dec 2010, Shaun Jackman wrote:
Hi,
I have a graph implementation where get(tag, graph, out_edge_iterator) is much more efficient than get(tag, graph, edge_descriptor) which is probably not an usual case.
Would it make sense for BGL to provide a default implementation of the former that dereferences the iterator and calls the latter? Graphs for which the former is more efficient could then specialize this function template.
I don't see many use cases where an iterator would be that much faster to access properties from than an edge descriptor. If the performance is really a lot better for your implementation, you can store a copy of the iterator (or whatever information from it needed to get the properties more quickly) into the edge descriptor itself.
-- Jeremiah Willcock