没有Boost的现代C++中的bimap实现

Question

我承认这个问题在此之前已经被问到,但是现在是4年前,我敢于要求更新:

我需要一种方法来将一个元组/对添加到容器中并有效地搜索左侧和右侧元素.

升压具有bimap和multi_index该做的正是我想要的,但我不知道什么是纯现代C++推荐的替代方案- 11/14如果你不希望引入的依赖性提高(无论何种原因).

链接中的一个答案表明不需要s.th. 由于透明的比较器,更像是一个bimap .接受的答案表明将std::maps与key1- > key2和key2- > 组合在一起的实现key1.

我真的不知道透明比较器如何帮助我,我只是好奇是否有一些这是你应该怎么做以及为什么 - 解决方案.你能提供一些提示/链接吗？

Answer 1

我认为这只是一些繁琐的工作.

为了好玩,我打算在这里实现一个起点.

Live On Coliru

笔记:

• "主要"支持是一个std::list<tuple<K,V>>.这可以确保迭代器/引用失效语义接近std::map越好
• 主要支持兼作"左"视图(仅供外部使用的只读)
• "右"视图非常相似,但使用了一个,std::reference_wrapper<value_type const>所以我们只对第一个容器进行索引

我只实现了简单的查询(lower_bound,upper_bound,equal_range和find).当然有迭代器和远程函数.

你还有一些要做的事情(erase,emplace范围插入,初始化器列表构造;有状态分配器/比较器支持是粗略的(没有构造函数采用相关参数),但是已经考虑了范围分配器.)

无需再费周折:

#include <algorithm>
#include <tuple>
#include <list>
#include <functional> // for std::reference_wrapper
#include <cassert>

namespace bimap {
    namespace detail {
        template <typename Cmp, typename V, size_t I> struct CompareByElement : private Cmp {
            bool operator()(V const& a, V const& b) const {
                using std::get;
                return Cmp::operator()(get<I>(a), get<I>(b));
            }
            bool operator()(V const& a, V const& b) {
                using std::get;
                return Cmp::operator()(get<I>(a), get<I>(b));
            }
        };

        namespace tags {
            struct left_view;
            struct right_view;
        }

        template <typename ViewTag, typename Left, typename Right, typename LeftCmp, typename RightCmp, typename RawAlloc>
        struct view_traits;

        template <typename Left, typename Right, typename LeftCmp, typename RightCmp, typename RawAlloc>
        struct view_traits<tags::left_view, Left, Right, LeftCmp, RightCmp, RawAlloc> {
            using value_type     = std::tuple<Left, Right>;
            using allocator_type = typename RawAlloc::template rebind<value_type>::other;
            using base_type      = std::list<value_type, allocator_type>;
            using comparator     = CompareByElement<LeftCmp, value_type, 0>;
        };

        template <typename Left, typename Right, typename LeftCmp, typename RightCmp, typename RawAlloc>
        struct view_traits<tags::right_view, Left, Right, LeftCmp, RightCmp, RawAlloc> {
            using value_type     = std::tuple<Left, Right>;
            using allocator_type = typename RawAlloc::template rebind<std::reference_wrapper<value_type const>>::other;
            using base_type      = std::list<std::reference_wrapper<value_type const>, allocator_type>;
            using comparator     = CompareByElement<RightCmp, value_type, 1>;
        };

        template <typename Left, typename Right, typename LeftCmp, typename RightCmp, typename RawAlloc>
        struct bimap_traits {
            using left_traits = view_traits<tags::left_view,  Left, Right, LeftCmp, RightCmp, RawAlloc>;
            using right_traits = view_traits<tags::right_view, Left, Right, LeftCmp, RightCmp, RawAlloc>;
        };

        template <typename Traits> struct map_adaptor : 
            private Traits::base_type,
            private Traits::comparator // empty base class optimization
        {
            using value_type     = typename Traits::value_type;
            using allocator_type = typename Traits::allocator_type;
            using base_type      = typename Traits::base_type;
            using comparator     = typename Traits::comparator;

            using iterator       = typename base_type::iterator;
            using const_iterator = typename base_type::const_iterator;

            using base_type::cbegin;
            using base_type::cend;
            using base_type::begin;
            using base_type::end;
            using base_type::insert;
            using base_type::size;

            auto lower_bound(value_type const& v)       { return std::lower_bound(base_type::begin(), base_type::end(), v, get_comp()); }
            auto upper_bound(value_type const& v)       { return std::upper_bound(base_type::begin(), base_type::end(), v, get_comp()); }
            auto equal_range(value_type const& v)       { return std::equal_range(base_type::begin(), base_type::end(), v, get_comp()); }
            auto lower_bound(value_type const& v) const { return std::lower_bound(base_type::begin(), base_type::end(), v, get_comp()); }
            auto upper_bound(value_type const& v) const { return std::upper_bound(base_type::begin(), base_type::end(), v, get_comp()); }
            auto equal_range(value_type const& v) const { return std::equal_range(base_type::begin(), base_type::end(), v, get_comp()); }

            auto find(value_type const& v) { 
                auto er = equal_range(v);
                return er.first == er.second? end() : er.first;
            }

            auto find(value_type const& v) const { 
                auto er = equal_range(v);
                return er.first == er.second? end() : er.first;
            }

            base_type& base()                  { return *static_cast<base_type*>(this);       } 
            base_type const & base() const     { return *static_cast<base_type const*>(this); } 
          private:
            comparator& get_comp()             { return *this;                                } 
            comparator const& get_comp() const { return *this;                                } 
        };
    }

    template <typename Left, typename Right, 
            typename LeftCmp = std::less<Left>, typename RightCmp = std::less<Right>,
            typename RawAlloc = std::allocator<void>,
            typename Traits = detail::bimap_traits<Left, Right, LeftCmp, RightCmp, RawAlloc>
        >
    class bimap : private detail::map_adaptor<typename Traits::left_traits> {
    public:
        using left_type      = typename detail::map_adaptor<typename Traits::left_traits>;
        using right_type     = typename detail::map_adaptor<typename Traits::right_traits>;

        using value_type     = typename Traits::left_traits::value_type;
        using allocator_type = typename Traits::left_traits::allocator_type;
        using base_type      = left_type;

        using const_iterator = typename base_type::const_iterator;
        using iterator       = const_iterator;

        using base_type::cbegin;
        using base_type::cend;
        auto begin() const { return cbegin(); }
        auto end() const { return cend(); }
        using base_type::size;

        left_type  const& left()  const { return *this;         }
        right_type const& right() const { return inverse_index; }

        std::pair<const_iterator, bool> insert(value_type const& v) {
            auto lr = left().find(v);
            auto rr = right().find(v);

            bool hasl = lr!=left().end(),
                 hasr = rr!=right().end();

            if (!hasl && !hasr) {
                auto lins = mutable_left().insert(left().lower_bound(v), v);
                auto rins = mutable_right().insert(right().lower_bound(*lins), *lins);
                (void) rins;

                return { lins, true };
            } else {
                return { end(), false };
            }
        }

    private:
        detail::map_adaptor<typename Traits::right_traits> inverse_index;
        left_type&  mutable_left()  { return *this;         }
        right_type& mutable_right() { return inverse_index; }
    };
}

#include <iostream>

#define CHECK(cond) do {\
    if (cond) { } else { std::cout << "FAILED: " #cond "\n"; } } while(false)

int main() {
    using Map = bimap::bimap<int, std::string>;
    Map bm;
    CHECK(bm.insert(std::make_tuple(1,"three")).second);

    // now left 1 and right "three" are taken:
    CHECK(!bm.insert(std::make_tuple(1,"two")).second);
    CHECK(!bm.insert(std::make_tuple(2,"three")).second);

    // unrelated keys insert fine
    CHECK(bm.insert(std::make_tuple(2,"aaaa")).second);

    // thing contains 2 elements now:
    CHECK(bm.size() == 2);

    using std::get;

    for (Map::value_type const& p : bm)         std::cout << get<0>(p) << ", " << get<1>(p) << "; "; std::cout << "\n";
    for (Map::value_type const& p : bm.left())  std::cout << get<0>(p) << ", " << get<1>(p) << "; "; std::cout << "\n";

    // right view map orders by right index
    for (Map::value_type const& p : bm.right()) std::cout << get<0>(p) << ", " << get<1>(p) << "; "; std::cout << "\n";

    // you can do find, lower_bound, equal_range etc. on both sides
}

打印:

1, three; 2, aaaa; 
1, three; 2, aaaa; 
2, aaaa; 1, three;