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fix: remove dependency to MPL in graph_traits using detector idiom #528

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Merged
Becheler merged 1 commit into from
Jul 16, 2026
+42 −35
Merged

fix: remove dependency to MPL in graph_traits using detector idiom #528

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77 changes: 42 additions & 35 deletions include/boost/graph/graph_traits.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,15 +14,12 @@
#include <iterator>
#include <utility> /* Primarily for std::pair */
#include <boost/tuple/tuple.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/mpl/not.hpp>
#include <boost/mpl/has_xxx.hpp>
#include <boost/mpl/void.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/mpl/and.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/type_traits/make_void.hpp>
#include <type_traits>
#include <boost/iterator/iterator_categories.hpp>
#include <boost/iterator/iterator_adaptor.hpp>
#include <boost/pending/property.hpp>
Expand All @@ -33,16 +30,18 @@ namespace boost

namespace detail
{
#define BOOST_GRAPH_MEMBER_OR_VOID(name) \
BOOST_MPL_HAS_XXX_TRAIT_DEF(name) \
template < typename T > struct BOOST_JOIN(get_member_, name) \
{ \
typedef typename T::name type; \
}; \
template < typename T > \
struct BOOST_JOIN(get_opt_member_, name) \
: boost::mpl::eval_if_c< BOOST_JOIN(has_, name) < T >::value, BOOST_JOIN(get_member_, name)< T >, boost::mpl::identity< void > >\
{ \
// get_opt_member_##name<T>::type is T::name when that member type exists, void otherwise.
#define BOOST_GRAPH_MEMBER_OR_VOID(name) \
template < typename T, typename = void > \
struct BOOST_JOIN(get_opt_member_, name) \
{ \
using type = void; \
}; \
template < typename T > \
struct BOOST_JOIN(get_opt_member_, name)< T, \
boost::void_t< typename T::name > > \
{ \
using type = typename T::name; \
};
BOOST_GRAPH_MEMBER_OR_VOID(adjacency_iterator)
BOOST_GRAPH_MEMBER_OR_VOID(out_edge_iterator)
Expand Down Expand Up @@ -282,40 +281,47 @@ typedef boost::forward_traversal_tag multi_pass_input_iterator_tag;

namespace detail
{
BOOST_MPL_HAS_XXX_TRAIT_DEF(graph_property_type)
BOOST_MPL_HAS_XXX_TRAIT_DEF(edge_property_type)
BOOST_MPL_HAS_XXX_TRAIT_DEF(vertex_property_type)

template < typename G > struct get_graph_property_type
// When the member type is present these expose it as ::type
// when absent they inherit no_property and expose no nested ::type.
template < typename G, typename = void >
struct get_graph_property_type : no_property
{
};
template < typename G >
struct get_graph_property_type< G, boost::void_t< typename G::graph_property_type > >
{
using type = typename G::graph_property_type;
};
template < typename G, typename = void >
struct get_edge_property_type : no_property
{
};
template < typename G >
struct get_edge_property_type< G, boost::void_t< typename G::edge_property_type > >
{
typedef typename G::graph_property_type type;
using type = typename G::edge_property_type;
};
template < typename G > struct get_edge_property_type
template < typename G, typename = void >
struct get_vertex_property_type : no_property
{
typedef typename G::edge_property_type type;
};
template < typename G > struct get_vertex_property_type
template < typename G >
struct get_vertex_property_type< G, boost::void_t< typename G::vertex_property_type > >
{
typedef typename G::vertex_property_type type;
using type = typename G::vertex_property_type;
};
}

template < typename G >
struct graph_property_type
: boost::mpl::eval_if< detail::has_graph_property_type< G >,
detail::get_graph_property_type< G >, no_property >
struct graph_property_type : detail::get_graph_property_type< G >
{
};
template < typename G >
struct edge_property_type
: boost::mpl::eval_if< detail::has_edge_property_type< G >,
detail::get_edge_property_type< G >, no_property >
struct edge_property_type : detail::get_edge_property_type< G >
{
};
template < typename G >
struct vertex_property_type
: boost::mpl::eval_if< detail::has_vertex_property_type< G >,
detail::get_vertex_property_type< G >, no_property >
struct vertex_property_type : detail::get_vertex_property_type< G >
{
};

Expand All @@ -341,7 +347,8 @@ namespace graph
template < typename Graph, typename Descriptor > class bundled_result
{
typedef typename graph_traits< Graph >::vertex_descriptor Vertex;
typedef typename mpl::if_c< (is_same< Descriptor, Vertex >::value),
typedef typename std::conditional<
(is_same< Descriptor, Vertex >::value),
vertex_bundle_type< Graph >, edge_bundle_type< Graph > >::type
bundler;

Expand Down
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