Re: [Boost-users] [BGL] adding behaviour to nodes and edges

From: Doug Gregor (dgregor_at_[hidden])
Date: 2005-06-14 13:06:36

On Jun 14, 2005, at 9:44 AM, martin f krafft wrote:
> also sprach Doug Gregor <dgregor_at_[hidden]> [2005.06.14.1558 
> +0200]:
>>>   g[*ei].fn()
>>>   g[*vi].fn()
>>>
>>> This is rather awkward. Is there a better way?
>>
>> Not really. If you can come up with a more natural syntax to express
>> what you'd like to do, we can try to incorporate it into the BGL.
>
> I'll think about it. One trivial way would be to store properties in
> the descriptors, rather than keeping a list of properties indexed by
> descriptor in the graph instance. Has this been considered?

Yes. When bundled properties were originally added, we talked about 
allowing property access through "->" on vertex and edge descriptors, 
because it would be convenient.

Unfortunately it becomes a const-qualification nightmare. In the BGL 
now, descriptors just abstractly name a vertex or edge. To get to a 
property, you need to go through the graph (or, more commonly, a 
property map). If you have a const graph or property map, you get const 
property values; non-const graphs and property maps give non-const 
property values. If we put the properties in the descriptors, we need 
to have const and non-const descriptors, which then implies const and 
non-const versions of vertex_iterator, edge_iterator, 
out_edge_iterator, in_edge_iterator, and adjacency_iterator. The 
const_iterator/iterator difference in STL containers can get really 
annoying; this would be much worse.

        Doug