Re: [Boost-users] Graph Library - bundled properties, internal & external properties

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2005-03-09 18:06:18

On Mar 8, 2005, at 7:43 AM, Elvanör wrote:

> Hello everyone,
>
> this is my first post to the list so excuse me if I didn't get some 
> concepts right.

Welcome!

> Now to my question: as I am a new user, when I read the documentation 
> I decided to use the new bundled properties mechanism rather than the 
> old properties map methods. It was recommended in the documentation (I 
> would, btw, like to humbly point out that the documentation is not 
> very clear on this. The bundled properties explanation page is not 
> accessible from the content page and could confuse quite a lot of 
> people), and anyway I found that a lot simpler.

Ok, we'll work on that.

> But now I am running into troubles. First, are bundled properties 
> applicable to "external properties"?

Bundled properties only apply to internal properties.

>  To be honest, I don't really get the difference between internal and 
> external properties. Or do I have to use property maps (in the old 
> way) for external properties?

Bundled properties don't change external properties at all.

> Second, with bundled properties I have troubles with constructors. I 
> created a class myClass, that I will use as a struct for the bundled 
> properties. This class contains reference members so it needs a 
> constructor better than the default constructor without any arguments. 
> Creating a graph with these bundled properties doesn't allow me to use 
> another constructor than the default myClass() one, it seems. I think 
> it would be very good if I could create an array of myClass and then 
> point my Graph object to this array to use it as bundled properties. 
> Then I could do all the initialization I want cleanly.

I think that when you add an edge or vertex, you can just pass a 
myClass instance before the graph argument, e.g,,

   v = add_vertex(myClass(some_reference), g);

> My last problem is with the depth_first_search() algorithm... and of 
> course bundled properties. This algorithm takes a const Graph &; but I 
> want to be able to modify (while running the algorithm) the bundled 
> properties!! That is the whole point of running this algorithm. I 
> don't want to change the structure of the graph (the abstract graph - 
> links from vertices to edges, etc), while running the algorithm, of 
> course, but I do want to change when I want my bundled properties... 
> that is not possible (at least, not without compiler warnings, which I 
> don't like :-) due to the fact that depth_first_search expects a const 
> graph.

Yeah, this is an annoying problem. We'd like to be able to take either 
a const or a non-const graph, but doing so would require two overloads 
of the algorithm, which we really can't do (too much code!). I suggest 
that you put a non-const reference to the graph from within your 
visitor and use that instead of the graph that is passed to the event 
functions.

        Doug