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## Class template flat_multiset

boost::container::flat_multiset

## Synopsis

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

    template<typename Key, typename Compare = std::less<Key>,
             typename Allocator = new_allocator<Key> >
    class flat_multiset {
    public:
      // types
      typedef Key                                                                key_type;
      typedef Key                                                                value_type;
      typedef Compare                                                            key_compare;
      typedef Compare                                                            value_compare;
      typedef ::boost::container::allocator_traits< Allocator >                  allocator_traits_type;
      typedef ::boost::container::allocator_traits< Allocator >::pointer         pointer;
      typedef ::boost::container::allocator_traits< Allocator >::const_pointer   const_pointer;
      typedef ::boost::container::allocator_traits< Allocator >::reference       reference;
      typedef ::boost::container::allocator_traits< Allocator >::const_reference const_reference;
      typedef ::boost::container::allocator_traits< Allocator >::size_type       size_type;
      typedef ::boost::container::allocator_traits< Allocator >::difference_type difference_type;
      typedef Allocator                                                          allocator_type;
      typedef implementation_defined                                             stored_allocator_type;
      typedef implementation_defined                                             iterator;
      typedef implementation_defined                                             const_iterator;
      typedef implementation_defined                                             reverse_iterator;
      typedef implementation_defined                                             const_reverse_iterator;

      // construct/copy/destruct
      explicit flat_multiset();
      explicit flat_multiset(const Compare &,
                             const allocator_type & = allocator_type());
      explicit flat_multiset(const allocator_type &);
      template<typename InputIterator>
        flat_multiset(InputIterator, InputIterator, const Compare & = Compare(),
                      const allocator_type & = allocator_type());
      template<typename InputIterator>
        flat_multiset(InputIterator, InputIterator, const allocator_type &);
      template<typename InputIterator>
        flat_multiset(ordered_range_t, InputIterator, InputIterator,
                      const Compare & = Compare(),
                      const allocator_type & = allocator_type());
      flat_multiset(std::initializer_list< value_type >,
                    const Compare & = Compare(),
                    const allocator_type & = allocator_type());
      flat_multiset(std::initializer_list< value_type >, const allocator_type &);
      flat_multiset(ordered_unique_range_t, std::initializer_list< value_type >,
                    const Compare & = Compare(),
                    const allocator_type & = allocator_type());
      flat_multiset(const flat_multiset &);
      flat_multiset(flat_multiset &&);
      flat_multiset(const flat_multiset &, const allocator_type &);
      flat_multiset(flat_multiset &&, const allocator_type &);
      flat_multiset & operator=(const flat_multiset &);
      flat_multiset & operator=(flat_multiset &&) noexcept(condition);
      flat_multiset & operator=(std::initializer_list< value_type >);

      // public member functions
      allocator_type get_allocator() const noexcept;
      stored_allocator_type & get_stored_allocator() noexcept;
      const stored_allocator_type & get_stored_allocator() const noexcept;
      iterator begin() noexcept;
      const_iterator begin() const;
      const_iterator cbegin() const noexcept;
      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 noexcept;
      size_type size() const noexcept;
      size_type max_size() const noexcept;
      size_type capacity() const noexcept;
      void reserve(size_type);
      void shrink_to_fit();
      template<class... Args> iterator emplace(Args &&...);
      template<class... Args> iterator emplace_hint(const_iterator, Args &&...);
      iterator insert(const value_type &);
      iterator insert(value_type &&);
      iterator insert(const_iterator, const value_type &);
      iterator insert(const_iterator, value_type &&);
      template<typename InputIterator> void insert(InputIterator, InputIterator);
      template<typename InputIterator>
        void insert(ordered_range_t, InputIterator, InputIterator);
      void insert(std::initializer_list< value_type >);
      void insert(ordered_range_t, std::initializer_list< value_type >);
      iterator erase(const_iterator);
      size_type erase(const key_type &);
      iterator erase(const_iterator, const_iterator);
      key_compare key_comp() const;
      value_compare value_comp() const;
      iterator find(const key_type &);
      const_iterator find(const key_type &) const;
      iterator nth(size_type) noexcept;
      const_iterator nth(size_type) const noexcept;
      size_type index_of(iterator) noexcept;
      size_type index_of(const_iterator) const noexcept;
      size_type count(const key_type &) const;
      iterator lower_bound(const key_type &);
      const_iterator lower_bound(const key_type &) const;
      iterator upper_bound(const key_type &);
      const_iterator upper_bound(const key_type &) const;
      std::pair< const_iterator, const_iterator >
      equal_range(const key_type &) const;
      std::pair< iterator, iterator > equal_range(const key_type &);

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

      // public data members
      void swap(flat_multiset &x) noexcept(allocator_traits_type void clear;
    };

## Description

flat_multiset is a Sorted Associative Container that stores objects of type Key.

flat_multiset can store multiple copies of the same key value.

flat_multiset is similar to std::multiset but it's implemented like an ordered vector. This means that inserting a new element into a flat_multiset invalidates previous iterators and references

Erasing an element invalidates iterators and references pointing to elements that come after (their keys are bigger) the erased element.

This container provides random-access iterators.

### Template Parameters

1.     typename Key

   is the type to be inserted in the multiset, which is also the key_type

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

   is the comparison functor used to order keys

3.     typename Allocator = new_allocator<Key>

   is the allocator to be used to allocate memory for this container

### `flat_multiset` public construct/copy/destruct

1.     explicit flat_multiset();

   Effects: Default constructs an empty container.

   Complexity: Constant.

2.     explicit flat_multiset(const Compare & comp,
                              const allocator_type & a = allocator_type());

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

   Complexity: Constant.

3.     explicit flat_multiset(const allocator_type & a);

   Effects: Constructs an empty container using the specified allocator.

   Complexity: Constant.

4.     template<typename InputIterator>
         flat_multiset(InputIterator first, InputIterator last,
                       const Compare & comp = Compare(),
                       const allocator_type & a = allocator_type());

   Effects: Constructs an empty container 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 comp and otherwise N logN, where N is last - first.

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

   Effects: Constructs an empty container 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 comp and otherwise N logN, where N is last - first.

6.     template<typename InputIterator>
         flat_multiset(ordered_range_t, InputIterator first, InputIterator last,
                       const Compare & comp = Compare(),
                       const allocator_type & a = allocator_type());

   Effects: Constructs an empty `flat_multiset` 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.

7.     flat_multiset(std::initializer_list< value_type > il,
                     const Compare & comp = Compare(),
                     const allocator_type & a = allocator_type());

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

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

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

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

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

9.     flat_multiset(ordered_unique_range_t, std::initializer_list< value_type > il,
                     const Compare & comp = Compare(),
                     const allocator_type & a = allocator_type());

   Effects: Constructs an empty container using the specified comparison object and allocator, and inserts elements from the ordered unique 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 and must be unique values.

   Complexity: Linear in N.

   Note: Non-standard extension.

10.     flat_multiset(const flat_multiset & x);

    Effects: Copy constructs the container.

    Complexity: Linear in x.size().

11.     flat_multiset(flat_multiset && x);

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

    Complexity: Constant.

    Postcondition: x is emptied.

12.     flat_multiset(const flat_multiset & x, const allocator_type & a);

    Effects: Copy constructs a container using the specified allocator.

    Complexity: Linear in x.size().

13.     flat_multiset(flat_multiset && x, const allocator_type & a);

    Effects: Move constructs a container using the specified allocator. Constructs *this using x's resources.

    Complexity: Constant if a == x.get_allocator(), linear otherwise

14.     flat_multiset & operator=(const flat_multiset & x);

    Effects: Makes *this a copy of x.

    Complexity: Linear in x.size().

15.     flat_multiset & operator=(flat_multiset && x) noexcept(condition);

    Throws: If allocator_traits_type::propagate_on_container_move_assignment is false and (allocation throws or value_type's move constructor throws)

    Complexity: Constant if allocator_traits_type:: propagate_on_container_move_assignment is true or this->get>allocator() == x.get_allocator(). Linear otherwise.

16.     flat_multiset & operator=(std::initializer_list< value_type > il);

    Effects: Copy all elements from il to *this.

    Complexity: Linear in il.size().

### `flat_multiset` public member functions

1.     allocator_type get_allocator() const noexcept;

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

   Complexity: Constant.

2.     stored_allocator_type & get_stored_allocator() noexcept;

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

3.     const stored_allocator_type & get_stored_allocator() const noexcept;

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

4.     iterator begin() noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

5.     const_iterator begin() const;

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

   Throws: Nothing.

   Complexity: Constant.

6.     const_iterator cbegin() const noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

7.     iterator end() noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

8.     const_iterator end() const noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

9.     const_iterator cend() const noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

10.     reverse_iterator rbegin() noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

11.     const_reverse_iterator rbegin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

12.     const_reverse_iterator crbegin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

13.     reverse_iterator rend() noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

14.     const_reverse_iterator rend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

15.     const_reverse_iterator crend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

16.     bool empty() const noexcept;

    Effects: Returns true if the container contains no elements.

    Throws: Nothing.

    Complexity: Constant.

17.     size_type size() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

18.     size_type max_size() const noexcept;

    Effects: Returns the largest possible size of the container.

    Throws: Nothing.

    Complexity: Constant.

19.     size_type capacity() const noexcept;

    Effects: Number of elements for which memory has been allocated. capacity() is always greater than or equal to size().

    Throws: Nothing.

    Complexity: Constant.

20.     void reserve(size_type cnt);

    Effects: If n is less than or equal to capacity(), this call has no effect. Otherwise, it is a request for allocation of additional memory. If the request is successful, then capacity() is greater than or equal to n; otherwise, capacity() is unchanged. In either case, size() is unchanged.

    Throws: If memory allocation allocation throws or Key's copy constructor throws.

    Note: If capacity() is less than "cnt", iterators and references to to values might be invalidated.

21.     void shrink_to_fit();

    Effects: Tries to deallocate the excess of memory created

    Throws: If memory allocation throws, or Key's copy constructor throws.

    Complexity: Linear to size().

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

    Effects: Inserts an object of type Key constructed with std::forward<Args>(args)... and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic search time plus linear insertion to the elements with bigger keys than x.

    Note: If an element is inserted it might invalidate elements.

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

    Effects: Inserts an object of type Key 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 search time (constant if x is inserted right before p) plus insertion linear to the elements with bigger keys than x.

    Note: If an element is inserted it might invalidate elements.

24.     iterator insert(const value_type & x);

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

    Complexity: Logarithmic search time plus linear insertion to the elements with bigger keys than x.

    Note: If an element is inserted it might invalidate elements.

25.     iterator insert(value_type && x);

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

    Complexity: Logarithmic search time plus linear insertion to the elements with bigger keys than x.

    Note: If an element is inserted it might invalidate elements.

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 search time (constant if x is inserted right before p) plus insertion linear to the elements with bigger keys than x.

    Note: If an element is inserted it might invalidate elements.

27.     iterator insert(const_iterator p, 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 search time (constant if x is inserted right before p) plus insertion linear to the elements with bigger keys than x.

    Note: If an element is inserted it might invalidate elements.

28.     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) search time plus N*size() insertion time.

    Note: If an element is inserted it might invalidate elements.

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

    Requires: first, last are not iterators into *this and must be ordered according to the predicate.

    Effects: inserts each element from the range [first,last) .This function is more efficient than the normal range creation for ordered ranges.

    Complexity: At most N log(size()+N) (N is the distance from first to last) search time plus N*size() insertion time.

    Note: Non-standard extension. If an element is inserted it might invalidate elements.

30.     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 first to last) search time plus N*size() insertion time.

    Note: If an element is inserted it might invalidate elements.

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

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

    Effects: inserts each element from the range [il.begin(), il.end()). This function is more efficient than the normal range creation for ordered ranges.

    Complexity: At most N log(size()+N) (N is the distance from il.begin() to il.end()) search time plus N*size() insertion time.

    Note: Non-standard extension. If an element is inserted it might invalidate elements.

32.     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: Linear to the elements with keys bigger than p

    Note: Invalidates elements with keys not less than the erased element.

33.     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: Logarithmic search time plus erasure time linear to the elements with bigger keys.

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

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

    Returns: Returns last.

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

    Complexity: Logarithmic search time plus erasure time linear to the elements with bigger keys.

35.     key_compare key_comp() const;

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

    Complexity: Constant.

36.     value_compare value_comp() const;

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

    Complexity: Constant.

37.     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.

38.     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.

39.     iterator nth(size_type n) noexcept;

    Requires: size() >= n.

    Effects: Returns an iterator to the nth element from the beginning of the container. Returns end() if n == size().

    Throws: Nothing.

    Complexity: Constant.

    Note: Non-standard extension

40.     const_iterator nth(size_type n) const noexcept;

    Requires: size() >= n.

    Effects: Returns a const_iterator to the nth element from the beginning of the container. Returns end() if n == size().

    Throws: Nothing.

    Complexity: Constant.

    Note: Non-standard extension

41.     size_type index_of(iterator p) noexcept;

    Requires: size() >= n.

    Effects: Returns an iterator to the nth element from the beginning of the container. Returns end() if n == size().

    Throws: Nothing.

    Complexity: Constant.

    Note: Non-standard extension

42.     size_type index_of(const_iterator p) const noexcept;

    Requires: begin() <= p <= end().

    Effects: Returns the index of the element pointed by p and size() if p == end().

    Throws: Nothing.

    Complexity: Constant.

    Note: Non-standard extension

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

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

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

44.     iterator lower_bound(const key_type & x);

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

    Complexity: Logarithmic

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

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

    Complexity: Logarithmic

46.     iterator upper_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

47.     const_iterator upper_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

48.     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

49.     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

### `flat_multiset` friend functions

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

   Effects: x.swap(y)

   Complexity: Constant.

### `flat_multiset` public public data members

1.     void swap(flat_multiset &x) noexcept(allocator_traits_type void clear;

   Effects: x.swap(y)

   Complexity: Constant.

   Effects: Swaps the contents of *this and x.

   Throws: Nothing.

   Complexity: Constant. Effects: erase(a.begin(),a.end()).

   Postcondition: size() == 0.

   Complexity: linear in size().