boost multiindex: lower_bound with value_type 作为参数

Question

我想将 lower_bound 与 Boost MultiIndex 容器的 value_type 一起使用。到目前为止，我只是设法通过显式提取成员来完成这项工作：

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/composite_key.hpp>
#include <boost/multi_index/member.hpp>
#include <string>

struct name {
    std::string firstname;
    std::string lastname;
    name(const std::string & firstname, const std::string & lastname) :
        firstname(firstname), lastname(lastname) {}
};

typedef boost::multi_index::multi_index_container<
    name,
    boost::multi_index::indexed_by<
        boost::multi_index::ordered_unique<
            boost::multi_index::composite_key<
                name,
                boost::multi_index::member<name, std::string, &name::lastname>,
                boost::multi_index::member<name, std::string, &name::firstname>
            >,
            boost::multi_index::composite_key_compare<
                std::less<std::string>,
                std::less<std::string>
            >
        >
    >
> NameIndex;

int main(void) {
    NameIndex nameindex;
    nameindex.insert(name("Alfred", "Ammer"));
    nameindex.insert(name("Martin", "Mauser"));
    // In my real code, I get this object passed.
    name lookupname("Hans", "Hoffer");

    // Does not compile
    //auto it = nameindex.get<0>().lower_bound(lookupname);

    // compiles, but I have to take explicitly list the members - in the right order
    auto it = nameindex.get<0>().lower_bound(std::make_tuple(lookupname.lastname, lookupname.firstname));
}

如何避免提取成员？

Answer 1

尝试以下操作：

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#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/composite_key.hpp>
#include <boost/multi_index/member.hpp>
#include <string>

struct name {
    std::string firstname;
    std::string lastname;
    name(const std::string & firstname, const std::string & lastname) :
        firstname(firstname), lastname(lastname) {}
};

struct name_compare:
    boost::multi_index::composite_key_compare<
        std::less<std::string>,
        std::less<std::string>
    >   
{
    using base=boost::multi_index::composite_key_compare<
        std::less<std::string>,
        std::less<std::string>
    >;

    using base::operator();

    template<typename T>
    bool operator()(const T& x,const name& y)const
    {
      return base::operator()(
          x,
          std::make_tuple(std::ref(y.firstname),std::ref(y.lastname)));
    }

    template<typename T>
    bool operator()(const name& x,const T& y)const
    {
      return base::operator()(
          std::make_tuple(std::ref(x.firstname),std::ref(x.lastname)),
          y);
    }
};

typedef boost::multi_index::multi_index_container<
    name,
    boost::multi_index::indexed_by<
        boost::multi_index::ordered_unique<
            boost::multi_index::composite_key<
                name,
                boost::multi_index::member<name, std::string, &name::lastname>,
                boost::multi_index::member<name, std::string, &name::firstname>
            >,
            name_compare
        >
    >
> NameIndex;

int main(void) {
    NameIndex nameindex;
    nameindex.insert(name("Alfred", "Ammer"));
    nameindex.insert(name("Martin", "Mauser"));
    // In my real code, I get this object passed.
    name lookupname("Hans", "Hoffer");

    auto it = nameindex.get<0>().lower_bound(lookupname);

    // this also works, as before

    it = nameindex.get<0>().lower_bound(std::make_tuple(lookupname.lastname, lookupname.firstname));
}

Answer 2

写

auto it = nameindex.get<0>().lower_bound(
    nameindex.get<0>().key_extractor()(lookupname));

boost multiindex: lower_bound with value_type 作为参数

boost multiindex: lower_bound with value_type as argument

c++

boost

boost-multi-index