Re: [boost] Re: Help needed with BGL & multi_index_container

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2005-01-31 12:45:57

Jeremy Siek ha escrito:

> In the docs
>
> http://www.boost.org/libs/graph/doc/using_adjacency_list.html
> #sec:choosing-graph-type
>
> it says that the container must meet the requirements of Sequence or
> RandomAccessContainer. Does multi_index_container meet these
> requirements? Also, the operations that are needed go through
> boost/pending/container_traits, so you may need to
> overload some functions like push() for multi_index_container.

Hi Jeremy,

>From the POV of adjacency_list, multi_index_container can work
as a sequence if its first index is of type sequenced. But I think this is
not the OP's intention. What he has in mind (I think) is having
multi_index_container function as a vertex store for adjacency_list
while presenting additional indices for the user's convenience. And I
think this cannot be done (in a simple manner) because adjacency_list
chooses internally the type of the vertices (namely, some integer type
from what I've been able to see in the source code): normally, one would
want to store richer elements than that. What is wanted is
a way to pass a predetermined instantiation of multi_index_container
so that adjcacency_list can use it as is.
One of the difficulties is that add_vertex is not passed an element
at all, instead adjacency_list creates it internally. The intended mode of
usage resembles more the following:

typedef multi_index_container<
  element_type,
  indexed_by<
    sequenced<>, // to be used by the BGL
    ... // other indices
  >
> multi_index_t;

typedef adjacency_list<
  vecS,
  // some way to have adjcaceny_list accept multi_index_t
  ...
> graph_t:

multi_index_t mic;
// populate mic
graph_t g;
// bind mic to g: g won't be mutable.
// use BGL with g

See what I mean? I don't know if I came any close to explain
myself clearly :) The first index of multi_index_t would act as the
vertex store of g, while at the same time the user can access
the elements through all the indices defined.

If Alexander (OP) does not agree with my analysis please tell me so.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

>
>
> Also, don't pass the address of the property into add_vertex, just
> pass by value.
>
> Cheers,
> Jeremy
>
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