| 1 | /// This is an example to demonstrate a problem I encountered with the
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| 2 | /// Boost Graph Library's (BGL) make_iterator_property_map when used
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| 3 | /// in conjunction with my own graph that has its property_map
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| 4 | /// specialization for vertex_index_t define the const_type as a true
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| 5 | /// const type.
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| 6 | ///
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| 7 | /// Is there a reason that make_iterator_property_map takes its second
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| 8 | /// argumant "by value" rather than "by referenc"e as the property_map
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| 9 | /// constructor does? This seems to cause an extra copy construction
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| 10 | /// to be performed that results in a non-const type which then does
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| 11 | /// does not match the property_map's constructor resulting in a
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| 12 | /// compilation error on GCC.
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| 13 |
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| 14 | #include "bug_report_example_skeleton.hpp"
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| 15 | #include <boost/graph/reverse_graph.hpp>
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| 16 | // #include "reverse_graph.hpp"
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| 17 |
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| 18 | void
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| 19 | bug_report_example_reverse_graph(MyGraph::Graph& g)
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| 20 | {
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| 21 | typedef boost::reverse_graph<MyGraph::Graph, MyGraph::Graph&> ReverseMyGraph;
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| 22 | /// The following does not compile because reverse_graph assumes
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| 23 | /// that the BidirectionalGraph template argument will have an
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| 24 | /// edge_property_type and a vertex_property_type. A user defined
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| 25 | /// graph that has been adapted by providing a specialization for
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| 26 | /// graph_traits and the other associated code may not have these
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| 27 | /// types as in this case.
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| 28 | ///
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| 29 | /// Looking at the code it seems these are only being used to
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| 30 | /// allow property_map's to be selected. An alternative way oif
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| 31 | /// achieving this is for reverse_graph to provide a
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| 32 | /// specialization for property_map that simply defines its
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| 33 | /// internals in terms of the base graph's property_map
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| 34 | /// specialization. This also simplifies the other code in
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| 35 | /// reverse_graph that is currently present to support
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| 36 | /// property_map selection.
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| 37 | ReverseMyGraph reverse_g = boost::make_reverse_graph(g);
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| 38 |
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| 39 | /// After fixing the above problem the following does not work
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| 40 | /// because the reverse_graph's definition for num_vertices
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| 41 | /// specifies the return type in terms of the base graphs
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| 42 | /// vertices_size_type. For a user defined graph that has been
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| 43 | /// adapted it may not have such a type as in this case.
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| 44 | ///
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| 45 | /// A solution is to change reverse_graph's num_vertices to use
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| 46 | /// graph_traits to obtain the type. This same problem exists on a
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| 47 | /// couple of other functions.
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| 48 | num_vertices(reverse_g);
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| 49 |
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| 50 | /// To be consistent some of the other functions need to specify
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| 51 | /// both arguments for reverse_graph rather then letting the
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| 52 | /// second one default.
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| 53 |
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| 54 | /// An ammended reverse_graph.hpp is provided that has these
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| 55 | /// changes and works with this example. I am not sure if some of
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| 56 | /// the property_map related code that is deleted is needed for
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| 57 | /// other reasons. It seems that just forwarding the property_map
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| 58 | /// of the reverse graph should avoid the need to provide these
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| 59 | /// other types that are used by the non-specialized version of
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| 60 | /// property_map. By providing an explicit specialization for
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| 61 | /// reverse_graph I think these will never be used.
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| 62 | }
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