Question

我有一个boost :: graph，它使用如下所示的捆绑属性：

struct Vertex
{
    std::string id;
};

如果我想在boost::dynamic_properties中使用此信息（例如以graphml格式打印），我可以使用类似的内容：

template<typename T>
std::string myPrettyPrinter(const T& t);

int main()
{
    using namespace boost;
    MyGraph g;
    dynamic_properties dp;
    dp.property("id",
        make_transform_value_property_map(
            & myPrettyPrinter<std::string>,
            get(&Vertex::id, g)
        )
    );
}

由于捆绑属性将来可能会发生变化，因此我希望对dynamic_properties的创建有所了解。因此，我使用boost :: fusion

struct Vertex
{
    std::string id;
};


BOOST_FUSION_ADAPT_STRUCT(
    Vertex,
    id
)


template<typename T>
std::string myPrettyPrinter(const T& t);


template <typename T_Seq, typename T_Graph>
void member_iterator(boost::dynamic_properties& dp, T_Graph& g)
{
    using namespace boost;
    using Indices = mpl::range_c<
        unsigned,
        0,
        fusion::result_of::size<T_Seq>::value
    >;

    fusion::for_each(
        Indices(),
        [&](auto i)
        {
            using I = decltype(i);
            dp.property(
                fusion::extension::struct_member_name<T_Seq, i>::call(),
                make_transform_value_property_map(
                    & myPrettyPrinter<
                        typename fusion::result_of::value_at<T_Seq, I>::type
                    >,
                    get(
                        // This works but is not generic,
                        // since it relies on the specific
                        // member name "id":
                        & T_Seq::id,
                        g
                    )
                )
            );
        }
    );
}


int main()
{
    MyGraph g;
    boost::dynamic_properties dp;
    member_iterator<Vertex>(dp, g);
}

我的问题是，我无法找到以通用方式表达行&T_Seq::id的方法。我一直在研究fusion::extension::struct_member_name，但没有成功。

我搜索一种替换有问题的行的通用方法或完全不同的方法来迭代Vertex的成员。

Answer 1

无论现有的答案是什么，我都会毫不犹豫地使用宏。

在这种情况下，由于boost::property_map<Graph, Tag>界面，我发现一切都变得困难了。我估计，你可以改用vertex_bundle_t。

这是一个简单的演示，根本不使用宏，它适用于顶点和边缘包。（您可以删除调试输出并重新添加漂亮的打印钩子。）

<强> Live On Coliru

#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/graphviz.hpp>
#include <boost/fusion/include/for_each.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/find.hpp>
#include <boost/phoenix/fusion/at.hpp>
#include <boost/phoenix.hpp>
#include <boost/mpl/range_c.hpp>

#include <iostream>

struct Vertex {
    std::string id;
    int numeric_value;
};
struct Edge {
    std::string more;
    int awesome_sauce;
};

BOOST_FUSION_ADAPT_STRUCT(Vertex, id, numeric_value)
BOOST_FUSION_ADAPT_STRUCT(Edge, more, awesome_sauce)

template <typename Tag, typename T_Graph>
void member_iterator(boost::dynamic_properties& dp, T_Graph& g)
{
    using namespace boost;

    using Bundle = typename boost::property_map<T_Graph, Tag>::type;
    using T_Seq  = typename boost::property_traits<Bundle>::value_type;

    using Indices = mpl::range_c<unsigned, 0, fusion::result_of::size<T_Seq>::value>;

    fusion::for_each(
        Indices{},
        [&, bundle=get(Tag{}, g)](auto i) {
            auto name = fusion::extension::struct_member_name<T_Seq, i>::call();
            std::cout << "Adding " << name << "\n";

            dp.property(
                name,
                make_transform_value_property_map(phoenix::at_c<i>(phoenix::arg_names::arg1), bundle)
            );
        }
    );
}

using MyGraph = boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS, Vertex, Edge>;

int main()
{
    MyGraph g;
    boost::dynamic_properties dp;

    member_iterator<boost::vertex_bundle_t>(dp, g);
    member_iterator<boost::edge_bundle_t>(dp, g);
}

打印

Adding id
Adding numeric_value
Adding more
Adding awesome_sauce

Answer 2

据我所知，您无法在内部从信息BOOST_FUSION_ADAPT_STRUCT存储中获取指向成员的指针（您可以，如您所见，获取成员类型或名称）。解决此问题的一种可能方法是创建一个调用BOOST_FUSION_ADAPT_STRUCT的宏，然后存储其他信息。我选择像这样存储它：

template<>
struct pointer_to_member_N<Vertex,0>
{
    static constexpr std::string Vertex::* value = &Vertex::id;
};

为了生成该结构，我使用以下宏：

#define YOUR_NS_SAVE_MEMBERPTR(STRUCT_NAME,MEMBERS) \
namespace your_ns { \
BOOST_PP_SEQ_FOR_EACH_I(CREATE_POINTER_TO_MEMBER_TRAIT,STRUCT_NAME,BOOST_PP_CAT(YOUR_NS_SAVE_MEMBERPTR_FILLER_0 MEMBERS,_END)) \
}

此宏采用结构名称和一对(type,name)对，只需打开名称空间your_ns并调用CREATE_POINTER_TO_MEMBER_TRAIT，每对传递STRUCT_NAME作为数据。

#define CREATE_POINTER_TO_MEMBER_TRAIT(R,STRUCT_NAME,INDEX,TYPE_AND_NAME) \
template <> struct pointer_to_member_N<STRUCT_NAME, INDEX>{ static constexpr BOOST_PP_TUPLE_ELEM(2,0,TYPE_AND_NAME) STRUCT_NAME::* value = &STRUCT_NAME::BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME); };

这是实际创建特征的那个。它需要一个参数R（我不知道它做了什么），你正在调整的结构的名称，当前成员的索引和一对(type,name)。它使用BOOST_PP_TUPLE_ELEM(2,N,TYPE_AND_NAME)来获取成员的类型或名称。

#include <iostream> 
#include <string>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/at.hpp>
#include <boost/fusion/include/for_each.hpp>
#include <boost/fusion/include/mpl.hpp>

#include <boost/mpl/range_c.hpp>

#include <cstddef>

namespace your_ns
{
    template <typename StructName, int N>
    struct pointer_to_member_N;
}

//Heavily "inspired" from BOOST_FUSION_ADAPT_STRUCT
#define YOUR_NS_SAVE_MEMBERPTR_FILLER_0(X, Y)  \
    ((X, Y)) YOUR_NS_SAVE_MEMBERPTR_FILLER_1
#define YOUR_NS_SAVE_MEMBERPTR_FILLER_1(X, Y)  \
    ((X, Y)) YOUR_NS_SAVE_MEMBERPTR_FILLER_0
#define YOUR_NS_SAVE_MEMBERPTR_FILLER_0_END
#define YOUR_NS_SAVE_MEMBERPTR_FILLER_1_END

#define CREATE_POINTER_TO_MEMBER_TRAIT(R,STRUCT_NAME,INDEX,TYPE_AND_NAME) \
template <> struct pointer_to_member_N<STRUCT_NAME, INDEX>{ static constexpr BOOST_PP_TUPLE_ELEM(2,0,TYPE_AND_NAME) STRUCT_NAME::* value = &STRUCT_NAME::BOOST_PP_TUPLE_ELEM(2,1,TYPE_AND_NAME); };

#define YOUR_NS_SAVE_MEMBERPTR(STRUCT_NAME,MEMBERS) \
namespace your_ns { \
BOOST_PP_SEQ_FOR_EACH_I(CREATE_POINTER_TO_MEMBER_TRAIT,STRUCT_NAME,BOOST_PP_CAT(YOUR_NS_SAVE_MEMBERPTR_FILLER_0 MEMBERS,_END)) \
}


#define ADAPT_STRUCT_AND_SAVE_MEMBERPTR(TYPE,MEMBERS) BOOST_FUSION_ADAPT_STRUCT(TYPE,MEMBERS) YOUR_NS_SAVE_MEMBERPTR(TYPE,MEMBERS)

   struct Vertex {
      std::string id;  
      std::size_t index;  
    };


ADAPT_STRUCT_AND_SAVE_MEMBERPTR(
  Vertex, 
  (std::string, id)
  (std::size_t, index)
)





int main() {
Vertex v; 
v.id="A";
v.index=0;

std::cout << std::mem_fn(your_ns::pointer_to_member_N<Vertex,0>::value)(v) << std::endl;
std::cout << v.*your_ns::pointer_to_member_N<Vertex,1>::value << std::endl;

}

使用boost :: fusion进行迭代时指向类成员的指针

2 个答案: