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<title>Bundled Properties</title>
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<h1>Bundled Properties</h1>
<p>Class templates <code><a
href="adjacency_list.html">adjacency_list</a></code> and
<code><a href="adjacency_matrix.html">adjacency_matrix</a></code> support
the introduction of named properties via <a
href="using_adjacency_list.html#sec:adjacency-list-properties">internal
properties</a>. However, this method is cumbersome in many uses,
where it would be more intuitive to just specify a structure or
class that contains internal properties for edges or
vertices. Bundled properties allow one to use
<code>adjacency_list</code> and <code>adjacency_matrix</code> in this
manner, providing a simple
way to introduce and access any number of internal properties
for vertices and edges.</p>
<p>One can introduce bundled properties into an
either graph type by providing a user-defined class
type for the <code>VertexProperties</code> or
<code>EdgeProperties</code> template arguments. The user-defined
class may alternatively be placed at the end of a
<code>property</code> list, replacing the (implicit)
<code>boost::no_property</code> argument.</p>
<h2>Example: Route planning</h2>
<p>Consider the implementation of a simple route planner that
should find the shortest directions from one city to another
via a set of highways. The vertices of the graph are cities,
and we may wish to store several bits of information about the
city within each vertex:</p>
<pre>
struct City
{
string name;
int population;
vector<int> zipcodes;
};
</pre>
<p>The edges in the graph represent highways, which also have
several interesting attributes:</p>
<pre>
struct Highway
{
string name;
double miles;
int speed_limit;
int lanes;
bool divided;
};
</pre>
<p>Without bundled properties, translating this example directly
into an instantiation of <code>adjacency_list</code> would
involve several custom properties and would result in a type
like this:</p>
<pre>
typedef boost::adjacency_list<
boost::listS, boost::vecS, boost::bidirectionalS,
// Vertex properties
boost::property<boost::vertex_name_t, std::string,
boost::property<population_t, int,
boost::property<zipcodes_t, std::vector<int> > > >,
// Edge properties
boost::property<boost::edge_name_t, std::string,
boost::property<boost::edge_length_t, double,
boost::property<edge_speed_limit_t, int,
boost::property<edge_lanes_t, int,
boost::property<edge_divided, bool> > > > > >
Map;
</pre>
<p>With bundled properties, we can directly use the
<code>City</code> and <code>Highway</code> structures:</p>
<pre>
typedef boost::adjacency_list<
boost::listS, boost::vecS, boost::bidirectionalS,
City, Highway> Map;
</pre>
<h2>Accessing bundled properties</h2>
<p>To access a bundled property for a particular edge or vertex,
subscript your graph with the descriptor of the edge or vertex
whose bundled property you wish to access. For instance:</p>
<pre>
Map map; // load the map
Map::vertex_descriptor v = *vertices(map).first;
map[v].name = "Troy";
map[v].population = 49170;
map[v].zipcodes.push_back(12180);
Map::edge_descriptor e = *out_edges(v, map).first;
map[e].name = "I-87";
map[e].miles = 10;
map[e].speed_limit = 65;
map[e].lanes = 4;
map[e].divided = true;
</pre>
<h2>Properties maps from bundled properties</h2>
<p>Often one needs to create a property map from an internal
property for use in a generic algorithm. For instance, using the
graph without bundled properties we might invoke <a
href="dijkstra_shortest_paths.html">Dijkstra's shortest
paths</a> algorithm like this:</p>
<pre>
vector<double> distances(num_vertices(map));
dijkstra_shortest_paths(map, from,
weight_map(get(edge_length, map))
.distance_map(make_iterator_property_map(distances.begin(),
get(vertex_index, map))));
</pre>
<p>With bundled properties, we can just pass a <em>member pointer</em>
as the property for <code>get</code>. The equivalent example
using bundled properties is:</p>
<pre>
vector<double> distances(num_vertices(map));
dijkstra_shortest_paths(map, from,
weight_map(get(<font color="#ff0000">&Highway::miles</font>, map))
.distance_map(make_iterator_property_map(distances.begin(),
get(vertex_index, map))));
</pre>
<p>The type of the returned property map is <code>property_map<Map, int Highway::*>::type</code>
or <code>property_map<Map, int Highway::*>::const_type</code>, depending on whether the graph
<code>map</code> is non-constant or constant.
<p> You may also access the entire vertex or edge bundle as a property map
using the <code>vertex_bundle</code> or <code>edge_bundle</code> properties,
respectively. For instance, the property map returned by <code>get(vertex_bundle, map)</code> is
an <a href="../../property_map/doc/LvaluePropertyMap.html">Lvalue Property Map</a> providing access to the
<code>City</code> values stored in each vertex.
<h2>Getting the type of bundled properties</h2>
<p>To get the type of the vertex or edge bundle for a given graph
type <tt>Graph</tt>, you can use the trait
classes <tt>vertex_bundle_type</tt>
and <tt>edge_bundle_type</tt>. The
type <tt>vertex_bundle_type<Graph>::type</tt> will be the
type bundled with vertices (or <tt>no_vertex_bundle</tt> if the
graph supports bundles but no vertex bundle
exists). Likewise, <tt>edge_bundle_type<Graph>::type</tt>
will be the type bundled with edges (or <tt>no_edge_bundle</tt> if
no edge bundle exists).</p>
<h2>Compatibility</h2> <p>Bundled properties will only work
properly on compilers that support class template partial
specialization.</p>
<hr>
Copyright © 2004 <a href="http://www.boost.org/people/doug_gregor.html">Doug Gregor</a>.
<address><a href="mailto:gregod@cs.rpi.edu"></a></address>
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