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Merged
Becheler merged 1 commit into from
Oct 9, 2026
Merged

feature: adding stateful visitor for dijkstra and astar #637

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2 changes: 1 addition & 1 deletion doc/modules/ROOT/pages/algorithms/shortest_paths/astar_search.adoc
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Expand Up @@ -541,4 +541,4 @@ See link:../example/astar-cities.cpp[`example/astar-cities.cpp`] for an example

== Notes

[#1]#[1]# Since the visitor parameter is passed by value, if your visitor contains state then any changes to the state during the algorithm will be made to a copy of the visitor object, not the visitor object passed in. Therefore you may want the visitor to hold this state by pointer or reference.
[#1]#[1]# The visitor is taken by value, so the algorithm works on a copy. To keep state, give the visitor ordinary data members and pass it with `std::ref`. The algorithm then operates on the referenced object and its state survives the call.
9 changes: 4 additions & 5 deletions doc/modules/ROOT/pages/algorithms/shortest_paths/dijkstra_shortest_paths.adoc
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Expand Up @@ -432,8 +432,7 @@ putting all _V - S_ vertices in the priority queue at once, but instead
only those vertices in _V - S_ that are discovered and therefore have a
distance less than infinity.

[#2]#[2]# Since the visitor parameter is passed by value, if
your visitor contains state then any changes to the state during the
algorithm will be made to a copy of the visitor object, not the visitor
object passed in. Therefore you may want the visitor to hold this state
by pointer or reference.
[#2]#[2]# The visitor is taken by value, so the algorithm works on a copy.
To keep state, give the visitor ordinary data members and pass it with
`std::ref`. The algorithm then operates on the referenced object and its
state survives the call.
9 changes: 4 additions & 5 deletions doc/modules/ROOT/pages/algorithms/spanning_trees/prim_minimum_spanning_tree.adoc
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Expand Up @@ -319,8 +319,7 @@ for an example of using Prim's algorithm.

== Notes

[#1]#[1]# Since the visitor parameter is passed by value, if
your visitor contains state then any changes to the state during the
algorithm will be made to a copy of the visitor object, not the visitor
object passed in. Therefore you may want the visitor to hold this state
by pointer or reference.
[#1]#[1]# The visitor is taken by value, so the algorithm works on a copy.
To keep state, give the visitor ordinary data members and pass it with
`std::ref`. The algorithm then operates on the referenced object and its
state survives the call.
60 changes: 36 additions & 24 deletions include/boost/graph/astar_search.hpp
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Expand Up @@ -21,6 +21,7 @@
#include <boost/graph/relax.hpp>
#include <boost/graph/exception.hpp>
#include <boost/graph/breadth_first_search.hpp>
#include <boost/graph/detail/visitor_wrapper.hpp>
#include <boost/graph/iteration_macros.hpp>
#include <boost/graph/detail/d_ary_heap.hpp>
#include <boost/graph/property_maps/constant_property_map.hpp>
Expand Down Expand Up @@ -50,7 +51,7 @@ template < class Graph, class CostType > class astar_heuristic
typedef Vertex argument_type;
typedef CostType result_type;
astar_heuristic() {}
CostType operator()(Vertex u) { return static_cast< CostType >(0); }
CostType operator()(Vertex /*u*/) { return static_cast< CostType >(0); }
};

template < class Visitor, class Graph > struct AStarVisitorConcept
Expand Down Expand Up @@ -92,11 +93,11 @@ class astar_visitor : public bfs_visitor< Visitors >
}

private:
template < class Edge, class Graph > void tree_edge(Edge e, const Graph& g)
template < class Edge, class Graph > void tree_edge(Edge /*e*/, const Graph& /*g*/)
{
}
template < class Edge, class Graph >
void non_tree_edge(Edge e, const Graph& g)
void non_tree_edge(Edge /*e*/, const Graph& /*g*/)
{
}
};
Expand Down Expand Up @@ -144,29 +145,29 @@ namespace detail
template < class Vertex, class Graph >
void initialize_vertex(Vertex u, const Graph& g)
{
m_vis.initialize_vertex(u, g);
user_vis().initialize_vertex(u, g);
}
template < class Vertex, class Graph >
void discover_vertex(Vertex u, const Graph& g)
{
m_vis.discover_vertex(u, g);
user_vis().discover_vertex(u, g);
}
template < class Vertex, class Graph >
void examine_vertex(Vertex u, const Graph& g)
{
m_vis.examine_vertex(u, g);
user_vis().examine_vertex(u, g);
}
template < class Vertex, class Graph >
void finish_vertex(Vertex u, const Graph& g)
{
m_vis.finish_vertex(u, g);
user_vis().finish_vertex(u, g);
}
template < class Edge, class Graph >
void examine_edge(Edge e, const Graph& g)
{
if (m_compare(get(m_weight, e), m_zero))
BOOST_THROW_EXCEPTION(negative_edge());
m_vis.examine_edge(e, g);
user_vis().examine_edge(e, g);
}
template < class Edge, class Graph >
void non_tree_edge(Edge, const Graph&)
Expand All @@ -182,13 +183,13 @@ namespace detail

if (m_decreased)
{
m_vis.edge_relaxed(e, g);
user_vis().edge_relaxed(e, g);
put(m_cost, target(e, g),
m_combine(
get(m_distance, target(e, g)), m_h(target(e, g))));
}
else
m_vis.edge_not_relaxed(e, g);
user_vis().edge_not_relaxed(e, g);
}

template < class Edge, class Graph >
Expand All @@ -204,10 +205,10 @@ namespace detail
m_combine(
get(m_distance, target(e, g)), m_h(target(e, g))));
m_Q.update(target(e, g));
m_vis.edge_relaxed(e, g);
user_vis().edge_relaxed(e, g);
}
else
m_vis.edge_not_relaxed(e, g);
user_vis().edge_not_relaxed(e, g);
}

template < class Edge, class Graph >
Expand All @@ -219,16 +220,21 @@ namespace detail

if (m_decreased)
{
m_vis.edge_relaxed(e, g);
user_vis().edge_relaxed(e, g);
put(m_cost, target(e, g),
m_combine(
get(m_distance, target(e, g)), m_h(target(e, g))));
m_Q.push(target(e, g));
put(m_color, target(e, g), Color::gray());
m_vis.black_target(e, g);
user_vis().black_target(e, g);
}
else
m_vis.edge_not_relaxed(e, g);
user_vis().edge_not_relaxed(e, g);
}

auto& user_vis()
{
return ::boost::graph::detail::deref_visitor(m_vis);
}

AStarHeuristic m_h;
Expand Down Expand Up @@ -310,38 +316,40 @@ inline void astar_search_no_init_tree(const VertexListGraph& g,
null_property_map< std::pair< Distance, Vertex >, std::size_t >(),
compare);

vis.discover_vertex(s, g);
auto& vis_ref = ::boost::graph::detail::deref_visitor(vis);

vis_ref.discover_vertex(s, g);
Q.push(std::make_pair(get(cost, s), s));
while (!Q.empty())
{
Vertex v;
Distance v_rank;
boost::tie(v_rank, v) = Q.top();
Q.pop();
vis.examine_vertex(v, g);
vis_ref.examine_vertex(v, g);
BGL_FORALL_OUTEDGES_T(v, e, g, VertexListGraph)
{
Vertex w = target(e, g);
vis.examine_edge(e, g);
vis_ref.examine_edge(e, g);
Distance e_weight = get(weight, e);
if (compare(e_weight, zero))
BOOST_THROW_EXCEPTION(negative_edge());
bool decreased
= relax(e, g, weight, predecessor, distance, combine, compare);
if (decreased)
{
vis.edge_relaxed(e, g);
vis_ref.edge_relaxed(e, g);
Distance w_rank = combine(get(distance, w), h(w));
put(cost, w, w_rank);
vis.discover_vertex(w, g);
vis_ref.discover_vertex(w, g);
Q.push(std::make_pair(w_rank, w));
}
else
{
vis.edge_not_relaxed(e, g);
vis_ref.edge_not_relaxed(e, g);
}
}
vis.finish_vertex(v, g);
vis_ref.finish_vertex(v, g);
}
}

Expand All @@ -361,14 +369,16 @@ inline void astar_search(const VertexListGraph& g,

typedef typename property_traits< ColorMap >::value_type ColorValue;
typedef color_traits< ColorValue > Color;
auto& vis_ref = ::boost::graph::detail::deref_visitor(vis);

typename graph_traits< VertexListGraph >::vertex_iterator ui, ui_end;
for (boost::tie(ui, ui_end) = vertices(g); ui != ui_end; ++ui)
{
put(color, *ui, Color::white());
put(distance, *ui, inf);
put(cost, *ui, inf);
put(predecessor, *ui, *ui);
vis.initialize_vertex(*ui, g);
vis_ref.initialize_vertex(*ui, g);
}
put(distance, s, zero);
put(cost, s, h(s));
Expand All @@ -390,13 +400,15 @@ inline void astar_search_tree(const VertexListGraph& g,
CostZero zero)
{

auto& vis_ref = ::boost::graph::detail::deref_visitor(vis);

typename graph_traits< VertexListGraph >::vertex_iterator ui, ui_end;
for (boost::tie(ui, ui_end) = vertices(g); ui != ui_end; ++ui)
{
put(distance, *ui, inf);
put(cost, *ui, inf);
put(predecessor, *ui, *ui);
vis.initialize_vertex(*ui, g);
vis_ref.initialize_vertex(*ui, g);
}
put(distance, s, zero);
put(cost, s, h(s));
Expand Down
36 changes: 22 additions & 14 deletions include/boost/graph/dijkstra_shortest_paths.hpp
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Expand Up @@ -26,6 +26,7 @@
#include <boost/graph/overloading.hpp>
#include <memory>
#include <boost/graph/detail/d_ary_heap.hpp>
#include <boost/graph/detail/visitor_wrapper.hpp>
#include <boost/graph/two_bit_color_map.hpp>
#include <boost/property_map/property_map.hpp>
#include <boost/property_map/vector_property_map.hpp>
Expand Down Expand Up @@ -97,7 +98,7 @@ class dijkstra_visitor : public bfs_visitor< Visitors >
}

private:
template < class Edge, class Graph > void tree_edge(Edge u, Graph& g) {}
template < class Edge, class Graph > void tree_edge(Edge /*u*/, Graph& /*g*/) {}
};
template < class Visitors >
dijkstra_visitor< Visitors > make_dijkstra_visitor(Visitors vis)
Expand Down Expand Up @@ -136,9 +137,9 @@ namespace detail
bool decreased = relax_target(e, g, m_weight, m_predecessor,
m_distance, m_combine, m_compare);
if (decreased)
m_vis.edge_relaxed(e, g);
user_vis().edge_relaxed(e, g);
else
m_vis.edge_not_relaxed(e, g);
user_vis().edge_not_relaxed(e, g);
}
template < class Edge, class Graph > void gray_target(Edge e, Graph& g)
{
Expand All @@ -149,27 +150,27 @@ namespace detail
if (decreased)
{
dijkstra_queue_update(m_Q, target(e, g), old_distance);
m_vis.edge_relaxed(e, g);
user_vis().edge_relaxed(e, g);
}
else
m_vis.edge_not_relaxed(e, g);
user_vis().edge_not_relaxed(e, g);
}

template < class Vertex, class Graph >
void initialize_vertex(Vertex u, Graph& g)
{
m_vis.initialize_vertex(u, g);
user_vis().initialize_vertex(u, g);
}
template < class Edge, class Graph > void non_tree_edge(Edge, Graph&) {}
template < class Vertex, class Graph >
void discover_vertex(Vertex u, Graph& g)
{
m_vis.discover_vertex(u, g);
user_vis().discover_vertex(u, g);
}
template < class Vertex, class Graph >
void examine_vertex(Vertex u, Graph& g)
{
m_vis.examine_vertex(u, g);
user_vis().examine_vertex(u, g);
}
template < class Edge, class Graph > void examine_edge(Edge e, Graph& g)
{
Expand Down Expand Up @@ -204,13 +205,18 @@ namespace detail
boost::throw_exception(negative_edge());
// End of test for negative-weight edges.

m_vis.examine_edge(e, g);
user_vis().examine_edge(e, g);
}
template < class Edge, class Graph > void black_target(Edge, Graph&) {}
template < class Vertex, class Graph >
void finish_vertex(Vertex u, Graph& g)
{
m_vis.finish_vertex(u, g);
user_vis().finish_vertex(u, g);
}

auto& user_vis()
{
return ::boost::graph::detail::deref_visitor(m_vis);
}

UniformCostVisitor m_vis;
Expand Down Expand Up @@ -250,8 +256,8 @@ namespace detail
struct vertex_property_map_generator_helper< Graph, IndexMap, Value, false >
{
typedef boost::vector_property_map< Value, IndexMap > type;
static type build(const Graph& g, const IndexMap& index,
std::unique_ptr< Value[] >& array_holder)
static type build(const Graph& /*g*/, const IndexMap& index,
std::unique_ptr< Value[] >& /*array_holder*/)
{
return boost::make_vector_property_map< Value >(index);
}
Expand Down Expand Up @@ -299,7 +305,7 @@ namespace detail
typedef boost::vector_property_map< boost::two_bit_color_type,
IndexMap >
type;
static type build(const Graph& g, const IndexMap& index)
static type build(const Graph& /*g*/, const IndexMap& index)
{
return boost::make_vector_property_map< boost::two_bit_color_type >(
index);
Expand Down Expand Up @@ -448,10 +454,12 @@ inline void dijkstra_shortest_paths(const VertexListGraph& g,
{
typedef typename property_traits< ColorMap >::value_type ColorValue;
typedef color_traits< ColorValue > Color;
auto& vis_ref = ::boost::graph::detail::deref_visitor(vis);

typename graph_traits< VertexListGraph >::vertex_iterator ui, ui_end;
for (boost::tie(ui, ui_end) = vertices(g); ui != ui_end; ++ui)
{
vis.initialize_vertex(*ui, g);
vis_ref.initialize_vertex(*ui, g);
put(distance, *ui, inf);
put(predecessor, *ui, *ui);
put(color, *ui, Color::white());
Expand Down
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