Re: [Boost-users] Newbie: What is the actual return type?

From: Douglas Paul Gregor (gregod_at_[hidden])
Date: 2004-06-19 22:16:39

On Sun, 20 Jun 2004, Tim Rowe wrote:

> In the Kevin Bacon example in the Boost::Graph documentation, we declare:
>   typedef adjacency_list < vecS, vecS, undirectedS, property < vertex_name_t,
>     std::string >, property < edge_name_t, std::string > > Graph;
>   Graph g;
>
> and later declare and call:
>
>   typedef property_map < Graph, vertex_name_t >::type actor_name_map_t;
>   actor_name_map_t actor_name = get(vertex_name, g);
>
> What are we actually getting back here? I can see that we can index it (we do later), but is it just an array? Or a vector? Or what? I assume I am /supposed/ to know (not like Ada's "type foo is private"), so that I know what I can do with it!

You're actually getting back an (Lvalue) property map. Think of it like an
std::map<vertex_descriptor, std::string>, because it maps from the
vertices in the graph g to the vertex name (which is an std::string here).
The difference is that the property map is fast (O(1)) whereas the
std::map would be slow (O(log |V|)).

Interior properties will get a bit easier with the next Boost release.

        Doug