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## Class template multimap

boost::container::multimap

## Synopsis

    // In header: <boost/container/map.hpp>

    template<typename Key, typename T, typename Compare = std::less<Key>,
             typename Allocator = new_allocator< std::pair< const Key, T> >,
             typename Options = tree_assoc_defaults>
    class multimap {
    public:
      // types
      typedef Key                                                                   key_type;
      typedef T                                                                     mapped_type;
      typedef base_t::allocator_type                                                allocator_type;
      typedef ::boost::container::allocator_traits< allocator_type >                allocator_traits_type;
      typedef boost::container::allocator_traits< allocator_type >::value_type      value_type;
      typedef boost::container::allocator_traits< allocator_type >::pointer         pointer;
      typedef boost::container::allocator_traits< allocator_type >::const_pointer   const_pointer;
      typedef boost::container::allocator_traits< allocator_type >::reference       reference;
      typedef boost::container::allocator_traits< allocator_type >::const_reference const_reference;
      typedef boost::container::allocator_traits< allocator_type >::size_type       size_type;
      typedef boost::container::allocator_traits< allocator_type >::difference_type difference_type;
      typedef implementation_defined                                                stored_allocator_type;
      typedef implementation_defined                                                value_compare;
      typedef Compare                                                               key_compare;
      typedef implementation_defined                                                iterator;
      typedef implementation_defined                                                const_iterator;
      typedef implementation_defined                                                reverse_iterator;
      typedef implementation_defined                                                const_reverse_iterator;
      typedef std::pair< key_type, mapped_type >                                    nonconst_value_type;
      typedef implementation_defined                                                movable_value_type;
      typedef implementation_defined                                                node_type;

      // construct/copy/destruct
      multimap() noexcept(dtl::is_nothrow_default_constructible< allocator_type >::value &&dtl::is_nothrow_default_constructible< Compare >::value));
      explicit multimap(const allocator_type &);
      explicit multimap(const Compare &);
      multimap(const Compare &, const allocator_type &);
      template<typename InputIterator> multimap(InputIterator, InputIterator);
      template<typename InputIterator>
        multimap(InputIterator, InputIterator, const allocator_type &);
      template<typename InputIterator>
        multimap(InputIterator, InputIterator, const Compare &);
      template<typename InputIterator>
        multimap(InputIterator, InputIterator, const Compare &,
                 const allocator_type &);
      template<typename InputIterator>
        multimap(ordered_range_t, InputIterator, InputIterator);
      template<typename InputIterator>
        multimap(ordered_range_t, InputIterator, InputIterator, const Compare &);
      template<typename InputIterator>
        multimap(ordered_range_t, InputIterator, InputIterator, const Compare &,
                 const allocator_type &);
      template<typename InputIterator>
        multimap(ordered_range_t, InputIterator, InputIterator,
                 const allocator_type &);
      multimap(std::initializer_list< value_type >);
      multimap(std::initializer_list< value_type >, const allocator_type &);
      multimap(std::initializer_list< value_type >, const Compare &);
      multimap(std::initializer_list< value_type >, const Compare &,
               const allocator_type &);
      multimap(ordered_range_t, std::initializer_list< value_type >);
      multimap(ordered_range_t, std::initializer_list< value_type >,
               const Compare &);
      multimap(ordered_range_t, std::initializer_list< value_type >,
               const Compare &, const allocator_type &);
      multimap(const multimap &);
      multimap(multimap &&) noexcept(boost::container::dtl::is_nothrow_move_constructible< Compare >::value));
      multimap(const multimap &, const allocator_type &);
      multimap(multimap &&, const allocator_type &);
      multimap & operator=(const multimap &);
      multimap & operator=(multimap &&) noexcept((allocator_traits_type::propagate_on_container_move_assignment::value||allocator_traits_type::is_always_equal::value) &&boost::container::dtl::is_nothrow_move_assignable< Compare >::value));
      multimap & operator=(std::initializer_list< value_type >);

      // public member functions
       BOOST_STATIC_ASSERT((dtl::is_same< typename allocator_type::value_type, std::pair< const Key, T > >::value));
      allocator_type get_allocator() const;
      stored_allocator_type & get_stored_allocator();
      const stored_allocator_type & get_stored_allocator() const;
      iterator begin();
      const_iterator begin() const;
      const_iterator cbegin() const;
      iterator end() noexcept;
      const_iterator end() const noexcept;
      const_iterator cend() const noexcept;
      reverse_iterator rbegin() noexcept;
      const_reverse_iterator rbegin() const noexcept;
      const_reverse_iterator crbegin() const noexcept;
      reverse_iterator rend() noexcept;
      const_reverse_iterator rend() const noexcept;
      const_reverse_iterator crend() const noexcept;
      bool empty() const;
      size_type size() const;
      size_type max_size() const;
      template<class... Args> iterator emplace(Args &&...);
      template<class... Args> iterator emplace_hint(const_iterator, Args &&...);
      iterator insert(const value_type &);
      iterator insert(const nonconst_value_type &);
      iterator insert(nonconst_value_type &&);
      iterator insert(movable_value_type &&);
      iterator insert(const_iterator, const value_type &);
      iterator insert(const_iterator, const nonconst_value_type &);
      iterator insert(const_iterator, nonconst_value_type &&);
      iterator insert(const_iterator, movable_value_type &&);
      template<typename InputIterator> void insert(InputIterator, InputIterator);
      void insert(std::initializer_list< value_type >);
      iterator insert(node_type &&);
      iterator insert(const_iterator, node_type &&);
      iterator erase(const_iterator);
      size_type erase(const key_type &);
      iterator erase(const_iterator, const_iterator);
      node_type extract(const key_type &);
      node_type extract(const_iterator);
      template<typename C2>
        void merge(multimap< Key, T, C2, Allocator, Options > &);
      template<typename C2>
        void merge(multimap< Key, T, C2, Allocator, Options > &&);
      template<typename C2> void merge(map< Key, T, C2, Allocator, Options > &);
      template<typename C2> void merge(map< Key, T, C2, Allocator, Options > &&);
      void swap(multiset &) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::dtl::is_nothrow_swappable< Compare >::value));
      void clear() noexcept;
      key_compare key_comp() const;
      value_compare value_comp() const;
      iterator find(const key_type &);
      const_iterator find(const key_type &) const;
      template<typename K> iterator find(const K &);
      template<typename K> const_iterator find(const K &) const;
      size_type count(const key_type &) const;
      template<typename K> size_type count(const K &) const;
      bool contains(const key_type &) const;
      template<typename K> bool contains(const K &) const;
      iterator lower_bound(const key_type &);
      const_iterator lower_bound(const key_type &) const;
      template<typename K> iterator lower_bound(const K &);
      template<typename K> const_iterator lower_bound(const K &) const;
      iterator upper_bound(const key_type &);
      const_iterator upper_bound(const key_type &) const;
      template<typename K> iterator upper_bound(const K &);
      template<typename K> const_iterator upper_bound(const K &) const;
      std::pair< iterator, iterator > equal_range(const key_type &);
      std::pair< const_iterator, const_iterator >
      equal_range(const key_type &) const;
      template<typename K> std::pair< iterator, iterator > equal_range(const K &);
      template<typename K>
        std::pair< const_iterator, const_iterator > equal_range(const K &) const;
      void rebalance();

      // friend functions
      friend bool operator==(const multimap &, const multimap &);
      friend bool operator!=(const multimap &, const multimap &);
      friend bool operator<(const multimap &, const multimap &);
      friend bool operator>(const multimap &, const multimap &);
      friend bool operator<=(const multimap &, const multimap &);
      friend bool operator>=(const multimap &, const multimap &);
      friend void swap(multimap &, multimap &);
    };

## Description

A multimap is a kind of associative container that supports equivalent keys (possibly containing multiple copies of the same key value) and provides for fast retrieval of values of another type T based on the keys. The multimap class supports bidirectional iterators.

A multimap satisfies all of the requirements of a container and of a reversible container and of an associative container. The `value_type` stored by this container is the value_type is std::pair<const Key, T>.

### Template Parameters

1.     typename Key

   is the key_type of the map

2.     typename T

3.     typename Compare = std::less<Key>

   is the ordering function for Keys (e.g. std::less<Key>).

4.     typename Allocator = new_allocator< std::pair< const Key, T> >

   is the allocator to allocate the `value_type`s (e.g. allocator< std::pair<const Key, T> > ).

5.     typename Options = tree_assoc_defaults

   is an packed option type generated using using `boost::container::tree_assoc_options`.

### `multimap` public construct/copy/destruct

1.     multimap() noexcept(dtl::is_nothrow_default_constructible< allocator_type >::value &&dtl::is_nothrow_default_constructible< Compare >::value));

   Effects: Default constructs an empty multimap.

   Complexity: Constant.

2.     explicit multimap(const allocator_type & a);

   Effects: Constructs an empty multimap using the specified allocator object and allocator.

   Complexity: Constant.

3.     explicit multimap(const Compare & comp);

   Effects: Constructs an empty multimap using the specified comparison.

   Complexity: Constant.

4.     multimap(const Compare & comp, const allocator_type & a);

   Effects: Constructs an empty multimap using the specified comparison and allocator.

   Complexity: Constant.

5.     template<typename InputIterator>
         multimap(InputIterator first, InputIterator last);

   Effects: Constructs an empty multimap and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

6.     template<typename InputIterator>
         multimap(InputIterator first, InputIterator last, const allocator_type & a);

   Effects: Constructs an empty multimap using the specified allocator, and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

7.     template<typename InputIterator>
         multimap(InputIterator first, InputIterator last, const Compare & comp);

   Effects: Constructs an empty multimap using the specified comparison object and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

8.     template<typename InputIterator>
         multimap(InputIterator first, InputIterator last, const Compare & comp,
                  const allocator_type & a);

   Effects: Constructs an empty multimap using the specified comparison object and allocator, and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

9.     template<typename InputIterator>
         multimap(ordered_range_t, InputIterator first, InputIterator last);

   Effects: Constructs an empty multimap and inserts elements from the ordered range [first ,last). This function is more efficient than the normal range creation for ordered ranges.

   Requires: [first ,last) must be ordered according to the predicate.

   Complexity: Linear in N.

   Note: Non-standard extension.

10.     template<typename InputIterator>
          multimap(ordered_range_t, InputIterator first, InputIterator last,
                   const Compare & comp);

    Effects: Constructs an empty multimap using the specified comparison object and inserts elements from the ordered range [first ,last). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [first ,last) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

11.     template<typename InputIterator>
          multimap(ordered_range_t, InputIterator first, InputIterator last,
                   const Compare & comp, const allocator_type & a);

    Effects: Constructs an empty multimap using the specified comparison object and allocator, and inserts elements from the ordered range [first ,last). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [first ,last) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

12.     template<typename InputIterator>
          multimap(ordered_range_t, InputIterator first, InputIterator last,
                   const allocator_type & a);

    Effects: Constructs an empty multimap using the specified allocator and inserts elements from the ordered range [first ,last). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [first ,last) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

13.     multimap(std::initializer_list< value_type > il);

    Effects: Constructs an empty multimap and and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is il.first() - il.end().

14.     multimap(std::initializer_list< value_type > il, const allocator_type & a);

    Effects: Constructs an empty multimap using the specified allocator, and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is il.first() - il.end().

15.     multimap(std::initializer_list< value_type > il, const Compare & comp);

    Effects: Constructs an empty multimap using the specified comparison object and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is il.first() - il.end().

16.     multimap(std::initializer_list< value_type > il, const Compare & comp,
                 const allocator_type & a);

    Effects: Constructs an empty multimap using the specified comparison object and allocator, and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is il.first() - il.end().

17.     multimap(ordered_range_t, std::initializer_list< value_type > il);

    Effects: Constructs an empty map and inserts elements from the ordered range [il.begin(), il.end()). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [il.begin(), il.end()) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

18.     multimap(ordered_range_t, std::initializer_list< value_type > il,
                 const Compare & comp);

    Effects: Constructs an empty map using the specified comparison object and inserts elements from the ordered range [il.begin(), il.end()). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [il.begin(), il.end()) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

19.     multimap(ordered_range_t, std::initializer_list< value_type > il,
                 const Compare & comp, const allocator_type & a);

    Effects: Constructs an empty map and inserts elements from the ordered range [il.begin(), il.end()). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [il.begin(), il.end()) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

20.     multimap(const multimap & x);

    Effects: Copy constructs a multimap.

    Complexity: Linear in x.size().

21.     multimap(multimap && x) noexcept(boost::container::dtl::is_nothrow_move_constructible< Compare >::value));

    Effects: Move constructs a multimap. Constructs *this using x's resources.

    Complexity: Constant.

    Postcondition: x is emptied.

22.     multimap(const multimap & x, const allocator_type & a);

    Effects: Copy constructs a multimap.

    Complexity: Linear in x.size().

23.     multimap(multimap && x, const allocator_type & a);

    Effects: Move constructs a multimap using the specified allocator. Constructs *this using x's resources. Complexity: Constant if a == x.get_allocator(), linear otherwise.

    Postcondition: x is emptied.

24.     multimap & operator=(const multimap & x);

    Effects: Makes *this a copy of x.

    Complexity: Linear in x.size().

25.     multimap & operator=(multimap && x) noexcept((allocator_traits_type::propagate_on_container_move_assignment::value||allocator_traits_type::is_always_equal::value) &&boost::container::dtl::is_nothrow_move_assignable< Compare >::value));

    Effects: this->swap(x.get()).

    Complexity: Constant.

26.     multimap & operator=(std::initializer_list< value_type > il);

    Effects: Assign content of il to *this.

### `multimap` public member functions

1.      BOOST_STATIC_ASSERT((dtl::is_same< typename allocator_type::value_type, std::pair< const Key, T > >::value));

2.     allocator_type get_allocator() const;

   Effects: Returns a copy of the allocator that was passed to the object's constructor.

   Complexity: Constant.

3.     stored_allocator_type & get_stored_allocator();

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

4.     const stored_allocator_type & get_stored_allocator() const;

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

5.     iterator begin();

   Effects: Returns an iterator to the first element contained in the container.

   Throws: Nothing.

   Complexity: Constant

6.     const_iterator begin() const;

   Effects: Returns a const_iterator to the first element contained in the container.

   Throws: Nothing.

   Complexity: Constant.

7.     const_iterator cbegin() const;

   Effects: Returns a const_iterator to the first element contained in the container.

   Throws: Nothing.

   Complexity: Constant.

8.     iterator end() noexcept;

   Effects: Returns an iterator to the end of the container.

   Throws: Nothing.

   Complexity: Constant.

9.     const_iterator end() const noexcept;

   Effects: Returns a const_iterator to the end of the container.

   Throws: Nothing.

   Complexity: Constant.

10.     const_iterator cend() const noexcept;

    Effects: Returns a const_iterator to the end of the container.

    Throws: Nothing.

    Complexity: Constant.

11.     reverse_iterator rbegin() noexcept;

    Effects: Returns a reverse_iterator pointing to the beginning of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

12.     const_reverse_iterator rbegin() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the beginning of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

13.     const_reverse_iterator crbegin() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the beginning of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

14.     reverse_iterator rend() noexcept;

    Effects: Returns a reverse_iterator pointing to the end of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

15.     const_reverse_iterator rend() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the end of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

16.     const_reverse_iterator crend() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the end of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

17.     bool empty() const;

    Effects: Returns true if the container contains no elements.

    Throws: Nothing.

    Complexity: Constant.

18.     size_type size() const;

    Effects: Returns the number of the elements contained in the container.

    Throws: Nothing.

    Complexity: Constant.

19.     size_type max_size() const;

    Effects: Returns the largest possible size of the container.

    Throws: Nothing.

    Complexity: Constant.

20.     template<class... Args> iterator emplace(Args &&... args);

    Effects: Inserts an object of type T constructed with std::forward<Args>(args)... in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

21.     template<class... Args>
          iterator emplace_hint(const_iterator p, Args &&... args);

    Effects: Inserts an object of type T constructed with std::forward<Args>(args)... in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

22.     iterator insert(const value_type & x);

    Effects: Inserts x and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic.

23.     iterator insert(const nonconst_value_type & x);

    Effects: Inserts a new value constructed from x and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic.

24.     iterator insert(nonconst_value_type && x);

    Effects: Inserts a new value move-constructed from x and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic.

25.     iterator insert(movable_value_type && x);

    Effects: Inserts a new value move-constructed from x and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic.

26.     iterator insert(const_iterator p, const value_type & x);

    Effects: Inserts a copy of x in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

27.     iterator insert(const_iterator p, const nonconst_value_type & x);

    Effects: Inserts a new value constructed from x in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

28.     iterator insert(const_iterator p, nonconst_value_type && x);

    Effects: Inserts a new value move constructed from x in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

29.     iterator insert(const_iterator p, movable_value_type && x);

    Effects: Inserts a new value move constructed from x in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

30.     template<typename InputIterator>
          void insert(InputIterator first, InputIterator last);

    Requires: first, last are not iterators into *this.

    Effects: inserts each element from the range [first,last) .

    Complexity: At most N log(size()+N) (N is the distance from first to last)

31.     void insert(std::initializer_list< value_type > il);

    Effects: inserts each element from the range [il.begin(), il.end().

    Complexity: At most N log(size()+N) (N is the distance from il.begin() to il.end())

32.     iterator insert(node_type && nh);

    Requires: nh is empty or this->get_allocator() == nh.get_allocator().

    Effects/Returns: If nh is empty, has no effect and returns end(). Otherwise, inserts the element owned by nh and returns an iterator pointing to the newly inserted element. If a range containing elements with keys equivalent to nh.key() exists, the element is inserted at the end of that range. nh is always emptied.

    Complexity: Logarithmic

33.     iterator insert(const_iterator hint, node_type && nh);

    Effects: Same as `insert(node_type && nh)` but the element is inserted as close as possible to the position just prior to "hint".

    Complexity: logarithmic in general, but amortized constant if the element is inserted right before "hint".

34.     iterator erase(const_iterator p);

    Effects: Erases the element pointed to by p.

    Returns: Returns an iterator pointing to the element immediately following q prior to the element being erased. If no such element exists, returns end().

    Complexity: Amortized constant time

35.     size_type erase(const key_type & x);

    Effects: Erases all elements in the container with key equivalent to x.

    Returns: Returns the number of erased elements.

    Complexity: log(size()) + count(k)

36.     iterator erase(const_iterator first, const_iterator last);

    Effects: Erases all the elements in the range [first, last).

    Returns: Returns last.

    Complexity: log(size())+N where N is the distance from first to last.

37.     node_type extract(const key_type & k);

    Effects: Removes the first element in the container with key equivalent to k.

    Returns: A node_type owning the element if found, otherwise an empty node_type.

    Complexity: log(size()).

38.     node_type extract(const_iterator position);

    Effects: Removes the element pointed to by "position".

    Returns: A node_type owning the element, otherwise an empty node_type.

    Complexity: Amortized constant.

39.     template<typename C2>
          void merge(multimap< Key, T, C2, Allocator, Options > & source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

40.     template<typename C2>
          void merge(multimap< Key, T, C2, Allocator, Options > && source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

41.     template<typename C2>
          void merge(map< Key, T, C2, Allocator, Options > & source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

42.     template<typename C2>
          void merge(map< Key, T, C2, Allocator, Options > && source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

43.     void swap(multiset & x) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::dtl::is_nothrow_swappable< Compare >::value));

    Effects: Swaps the contents of *this and x.

    Throws: Nothing.

    Complexity: Constant.

44.     void clear() noexcept;

    Effects: erase(begin(),end()).

    Postcondition: size() == 0.

    Complexity: linear in size().

45.     key_compare key_comp() const;

    Effects: Returns the comparison object out of which a was constructed.

    Complexity: Constant.

46.     value_compare value_comp() const;

    Effects: Returns an object of value_compare constructed out of the comparison object.

    Complexity: Constant.

47.     iterator find(const key_type & x);

    Returns: An iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

48.     const_iterator find(const key_type & x) const;

    Returns: A const iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

49.     template<typename K> iterator find(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: An iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

50.     template<typename K> const_iterator find(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: A const_iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

51.     size_type count(const key_type & x) const;

    Returns: The number of elements with key equivalent to x.

    Complexity: log(size())+count(k)

52.     template<typename K> size_type count(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: The number of elements with key equivalent to x.

    Complexity: log(size())+count(k)

53.     bool contains(const key_type & x) const;

    Returns: Returns true if there is an element with key equivalent to key in the container, otherwise false.

    Complexity: log(size()).

54.     template<typename K> bool contains(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: Returns true if there is an element with key equivalent to key in the container, otherwise false.

    Complexity: log(size()).

55.     iterator lower_bound(const key_type & x);

    Returns: An iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

56.     const_iterator lower_bound(const key_type & x) const;

    Returns: A const iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

57.     template<typename K> iterator lower_bound(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: An iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

58.     template<typename K> const_iterator lower_bound(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: A const iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

59.     iterator upper_bound(const key_type & x);

    Returns: An iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

60.     const_iterator upper_bound(const key_type & x) const;

    Returns: A const iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

61.     template<typename K> iterator upper_bound(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: An iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

62.     template<typename K> const_iterator upper_bound(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: A const iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

63.     std::pair< iterator, iterator > equal_range(const key_type & x);

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

64.     std::pair< const_iterator, const_iterator >
        equal_range(const key_type & x) const;

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

65.     template<typename K> std::pair< iterator, iterator > equal_range(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

66.     template<typename K>
          std::pair< const_iterator, const_iterator > equal_range(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

67.     void rebalance();

    Effects: Rebalances the tree. It's a no-op for Red-Black and AVL trees.

    Complexity: Linear

### `multimap` friend functions

1.     friend bool operator==(const multimap & x, const multimap & y);

   Effects: Returns true if x and y are equal

   Complexity: Linear to the number of elements in the container.

2.     friend bool operator!=(const multimap & x, const multimap & y);

   Effects: Returns true if x and y are unequal

   Complexity: Linear to the number of elements in the container.

3.     friend bool operator<(const multimap & x, const multimap & y);

   Effects: Returns true if x is less than y

   Complexity: Linear to the number of elements in the container.

4.     friend bool operator>(const multimap & x, const multimap & y);

   Effects: Returns true if x is greater than y

   Complexity: Linear to the number of elements in the container.

5.     friend bool operator<=(const multimap & x, const multimap & y);

   Effects: Returns true if x is equal or less than y

   Complexity: Linear to the number of elements in the container.

6.     friend bool operator>=(const multimap & x, const multimap & y);

   Effects: Returns true if x is equal or greater than y

   Complexity: Linear to the number of elements in the container.

7.     friend void swap(multimap & x, multimap & y);

   Effects: x.swap(y)

   Complexity: Constant.