Re: [Boost-users] BGL: shared_ptr as bundled properties > how to generate properties maps ???

Subject: Re: [Boost-users] BGL: shared_ptr as bundled properties > how to generate properties maps ???
From: Jeremiah Willcock (jewillco_at_[hidden])
Date: 2010-01-07 09:51:55

On Thu, 7 Jan 2010, Damien Maupu wrote:

>> On Wed, 6 Jan 2010, Emil Dotchevski wrote:
>
>> > On Wed, Jan 6, 2010 at 8:20 AM, Damien Maupu 
> <damien.maupu_at_[hidden]> wrote:
>>>> I write something like:
>>>> typedef boost::shared_ptr<Vertex> VertexPtr;
>>>> typedef boost::shared_ptr<Edge> EdgePtr;
>>>> typedef adjacency_list<vecS, vecS, directedS, VertexPtr, EdgePtr> 
> Graph;
>>>
>>> It is probably not a good idea to use shared_ptr for graphs; some
>>> graphs have cycles and this will lead to leaks (if your data structure
>>> is a DAG, you're fine.)
>
>> I don't think that will be an issue -- his shared pointers link to
>> properties; the graph structure itself is in BGL data structures.
>> However, if the properties refer to other graph vertices or edges, there
>> is an issue of dangling references if those objects are removed from the
>> graph.
>
>> -- Jeremiah Willcock
>
> Hi,
>
> I am not sure I understand why using smart pointer should be an issue.
> Could you explain me in little more details?
>
> Do you know how to get properties maps if bundle properties are pointer or 
> smart pointers?

The bundled property mechanism expects the bundled property template 
parameters (for vertices and edges) to be structs/classes that 
contain individual properties as members.  The get() function with a 
pointer to member gets the property map for an individual member of the 
struct.  Therefore, the default property map mechanism can only get the 
members of the shared_ptr itself, which I believe are private (and not the 
members of the pointed-to object, which you want).  Therefore, you need to 
use another mechanism to obtain property maps for objects pointed to by a 
bundled property.  It might be possible to use metaprogramming to make 
that automatic, but Boost.Graph does not contain that functionality 
currently.  The solution is to use something like function_property_map 
(the message you are replying to).

-- Jeremiah Willcock