| Home | Libraries | People | FAQ | More

## Class template flat_map

boost::container::flat_map

## Synopsis

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

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

      // public member functions
       BOOST_CONTAINER_STATIC_ASSERT((dtl::is_same< std::pair< Key, T >, value_type >::value));
      flat_map();
      explicit flat_map(const allocator_type &);
      explicit flat_map(const Compare &);
      flat_map(const Compare &, const allocator_type &);
      template<typename InputIterator> flat_map(InputIterator, InputIterator);
      template<typename InputIterator>
        flat_map(InputIterator, InputIterator, const allocator_type &);
      template<typename InputIterator>
        flat_map(InputIterator, InputIterator, const Compare &);
      template<typename InputIterator>
        flat_map(InputIterator, InputIterator, const Compare &,
                 const allocator_type &);
      template<typename InputIterator>
        flat_map(ordered_unique_range_t, InputIterator, InputIterator);
      template<typename InputIterator>
        flat_map(ordered_unique_range_t, InputIterator, InputIterator,
                 const Compare &);
      template<typename InputIterator>
        flat_map(ordered_unique_range_t, InputIterator, InputIterator,
                 const Compare &, const allocator_type &);
      template<typename InputIterator>
        flat_map(ordered_unique_range_t, InputIterator, InputIterator,
                 const allocator_type &);
      flat_map(std::initializer_list< value_type >);
      flat_map(std::initializer_list< value_type >, const allocator_type &);
      flat_map(std::initializer_list< value_type >, const Compare &);
      flat_map(std::initializer_list< value_type >, const Compare &,
               const allocator_type &);
      flat_map(ordered_unique_range_t, std::initializer_list< value_type >);
      flat_map(ordered_unique_range_t, std::initializer_list< value_type >,
               const Compare &);
      flat_map(ordered_unique_range_t, std::initializer_list< value_type >,
               const Compare &, const allocator_type &);
      flat_map(const flat_map &);
      flat_map(flat_map &&);
      flat_map(const flat_map &, const allocator_type &);
      flat_map(flat_map &&, const allocator_type &);
      flat_map & operator=(const flat_map &);
      flat_map & operator=(flat_map &&);
      flat_map & operator=(std::initializer_list< value_type >);
      allocator_type get_allocator() const noexcept;
      get_stored_allocator_noconst_return_t get_stored_allocator() noexcept;
      get_stored_allocator_const_return_t get_stored_allocator() const noexcept;
      iterator begin() noexcept;
      const_iterator begin() const noexcept;
      iterator end() noexcept;
      const_iterator end() const noexcept;
      reverse_iterator rbegin() noexcept;
      const_reverse_iterator rbegin() const noexcept;
      reverse_iterator rend() noexcept;
      const_reverse_iterator rend() const noexcept;
      const_iterator cbegin() const noexcept;
      const_iterator cend() const noexcept;
      const_reverse_iterator crbegin() 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();
      mapped_type & operator[](const key_type &);
      mapped_type & operator[](key_type &&);
      template<typename K> mapped_type & operator[](K &&);
      template<typename M>
        std::pair< iterator, bool > insert_or_assign(const key_type &, M &&);
      template<typename M>
        std::pair< iterator, bool > insert_or_assign(key_type &&, M &&);
      template<typename K, typename M>
        std::pair< iterator BOOST_MOVE_I bool > insert_or_assign(K &&, M &&);
      template<typename M>
        iterator insert_or_assign(const_iterator, const key_type &, M &&);
      template<typename M>
        iterator insert_or_assign(const_iterator, key_type &&, M &&);
      template<typename K, typename M>
        iterator insert_or_assign(const_iterator, K &&, M &&);
      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;
      T & at(const key_type &);
      const T & at(const key_type &) const;
      template<typename K> T & at(const K &);
      template<typename K> const T & at(const K &) const;
      template<class... Args> std::pair< iterator, bool > emplace(Args &&...);
      template<class... Args> iterator emplace_hint(const_iterator, Args &&...);
      template<class... Args>
        std::pair< iterator, bool > try_emplace(const key_type &, Args &&...);
      template<class... Args>
        iterator try_emplace(const_iterator, const key_type &, Args &&...);
      template<class... Args>
        std::pair< iterator, bool > try_emplace(key_type &&, Args &&...);
      template<class... Args>
        iterator try_emplace(const_iterator, key_type &&, Args &&...);
      template<typename K, class... Args>
        std::pair< iterator BOOST_MOVE_I bool > try_emplace(K &&, Args &&...);
      template<typename K, class... Args>
        iterator try_emplace(const_iterator, K &&, Args &&...);
      std::pair< iterator, bool > insert(const value_type &);
      std::pair< iterator, bool > insert(value_type &&);
      template<typename Pair>
        std::pair< iterator BOOST_MOVE_I bool > insert(Pair &&);
      iterator insert(const_iterator, const value_type &);
      iterator insert(const_iterator, value_type &&);
      template<typename Pair> iterator insert(const_iterator, Pair &&);
      template<typename InputIterator> void insert(InputIterator, InputIterator);
      template<typename InputIterator>
        void insert(ordered_unique_range_t, InputIterator, InputIterator);
      void insert(std::initializer_list< value_type >);
      void insert(ordered_unique_range_t, std::initializer_list< value_type >);
      template<typename C2>
        void merge(flat_map< Key, T, C2, AllocatorOrContainer > &);
      template<typename C2>
        void merge(flat_map< Key, T, C2, AllocatorOrContainer > &&);
      template<typename C2>
        void merge(flat_multimap< Key, T, C2, AllocatorOrContainer > &);
      template<typename C2>
        void merge(flat_multimap< Key, T, C2, AllocatorOrContainer > &&);
      iterator erase(const_iterator);
      size_type erase(const key_type &);
      template<typename K> size_type erase(K &&);
      iterator erase(const_iterator, const_iterator);
      void swap(flat_map &);
      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;
      sequence_type extract_sequence();
      void adopt_sequence(sequence_type &&);
      void adopt_sequence(ordered_unique_range_t, sequence_type &&);
      const sequence_type & sequence() const noexcept;

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

## Description

A flat_map is a kind of associative container that supports unique keys (contains at most one of each key value) and provides for fast retrieval of values of another type T based on the keys.

A flat_map satisfies all of the requirements of a container, a reversible container and an associative container. A flat_map also provides most operations described for unique keys. For a flat_map<Key,T> the key_type is Key and the value_type is std::pair<Key,T> (unlike std::map<Key, T> which value_type is std::pair<const Key, T>).

flat_map is similar to std::map but it's implemented by as an ordered sequence container. The underlying sequence container is by default vector but it can also work user-provided vector-like SequenceContainers (like static_vector or small_vector).

Using vector-like sequence containers means that inserting a new element into a flat_map might invalidate previous iterators and references (unless that sequence container is stable_vector or a similar container that offers stable pointers and references). Similarly, erasing an element might invalidate 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 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 AllocatorOrContainer = new_allocator< std::pair< Key, T> >

   is either:

   - The allocator to allocate `value_type`s (e.g. allocator< std::pair<Key, T> > ). (in this case sequence_type will be vector<value_type, AllocatorOrContainer>)

   - The SequenceContainer to be used as the underlying sequence_type. It must be a vector-like sequence container with random-access iterators.

### `flat_map` public member functions

1.      BOOST_CONTAINER_STATIC_ASSERT((dtl::is_same< std::pair< Key, T >, value_type >::value));

2.     flat_map();

   Effects: Default constructs an empty flat_map.

   Complexity: Constant.

3.     explicit flat_map(const allocator_type & a);

   Effects: Constructs an empty flat_map using the specified allocator.

   Complexity: Constant.

4.     explicit flat_map(const Compare & comp);

   Effects: Constructs an empty flat_map using the specified comparison object.

   Complexity: Constant.

5.     flat_map(const Compare & comp, const allocator_type & a);

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

   Complexity: Constant.

6.     template<typename InputIterator>
         flat_map(InputIterator first, InputIterator last);

   Effects: Constructs an empty flat_map and 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>
         flat_map(InputIterator first, InputIterator last, const allocator_type & a);

   Effects: Constructs an empty flat_map 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.

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

   Effects: Constructs an empty flat_map using the specified comparison object and 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>
         flat_map(InputIterator first, InputIterator last, const Compare & comp,
                  const allocator_type & a);

   Effects: Constructs an empty flat_map 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.

10.     template<typename InputIterator>
          flat_map(ordered_unique_range_t, InputIterator first, InputIterator last);

    Effects: Constructs an empty flat_map 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>
          flat_map(ordered_unique_range_t, InputIterator first, InputIterator last,
                   const Compare & comp);

    Effects: Constructs an empty flat_map 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.

12.     template<typename InputIterator>
          flat_map(ordered_unique_range_t, InputIterator first, InputIterator last,
                   const Compare & comp, const allocator_type & a);

    Effects: Constructs an empty flat_map 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.

13.     template<typename InputIterator>
          flat_map(ordered_unique_range_t, InputIterator first, InputIterator last,
                   const allocator_type & a);

    Effects: Constructs an empty flat_map 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.

14.     flat_map(std::initializer_list< value_type > il);

    Effects: Constructs an empty flat_map 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 the predicate and otherwise N logN, where N is last - first.

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

    Effects: Constructs an empty flat_map 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 the predicate and otherwise N logN, where N is last - first.

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

    Effects: Constructs an empty flat_map using the specified comparison object 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 the predicate and otherwise N logN, where N is last - first.

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

    Effects: Constructs an empty flat_map 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 the predicate and otherwise N logN, where N is last - first.

18.     flat_map(ordered_unique_range_t, std::initializer_list< value_type > il);

    Effects: Constructs an empty flat_map using 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.

19.     flat_map(ordered_unique_range_t, std::initializer_list< value_type > il,
                 const Compare & comp);

    Effects: Constructs an empty flat_map using the specified comparison object 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.

20.     flat_map(ordered_unique_range_t, std::initializer_list< value_type > il,
                 const Compare & comp, const allocator_type & a);

    Effects: Constructs an empty flat_map 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.

21.     flat_map(const flat_map & x);

    Effects: Copy constructs a flat_map.

    Complexity: Linear in x.size().

22.     flat_map(flat_map && x);

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

    Complexity: Constant.

    Postcondition: x is emptied.

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

    Effects: Copy constructs a flat_map using the specified allocator.

    Complexity: Linear in x.size().

24.     flat_map(flat_map && x, const allocator_type & a);

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

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

25.     flat_map & operator=(const flat_map & x);

    Effects: Makes *this a copy of x.

    Complexity: Linear in x.size().

26.     flat_map & operator=(flat_map && x);

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

    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.

27.     flat_map & operator=(std::initializer_list< value_type > il);

    Effects: Assign elements from il to *this

28.     allocator_type get_allocator() const noexcept;

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

    Complexity: Constant.

29.     get_stored_allocator_noconst_return_t get_stored_allocator() noexcept;

    Effects: Returns a reference to the internal allocator.

    Throws: Nothing

    Complexity: Constant.

    Note: Non-standard extension.

30.     get_stored_allocator_const_return_t get_stored_allocator() const noexcept;

    Effects: Returns a reference to the internal allocator.

    Throws: Nothing

    Complexity: Constant.

    Note: Non-standard extension.

31.     iterator begin() noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

32.     const_iterator begin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

33.     iterator end() noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

34.     const_iterator end() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

35.     reverse_iterator rbegin() noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

36.     const_reverse_iterator rbegin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

37.     reverse_iterator rend() noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

38.     const_reverse_iterator rend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

39.     const_iterator cbegin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

40.     const_iterator cend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

41.     const_reverse_iterator crbegin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

42.     const_reverse_iterator crend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

43.     bool empty() const noexcept;

    Effects: Returns true if the container contains no elements.

    Throws: Nothing.

    Complexity: Constant.

44.     size_type size() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

45.     size_type max_size() const noexcept;

    Effects: Returns the largest possible size of the container.

    Throws: Nothing.

    Complexity: Constant.

46.     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.

47.     void reserve(size_type cnt);

    Effects: If n is less than or equal to capacity(), or the underlying container has no `reserve` member, 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 T's copy constructor throws.

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

48.     void shrink_to_fit();

    Effects: Tries to deallocate the excess of memory created

    Throws: If memory allocation throws, or T's copy constructor throws.

    Complexity: Linear to size().

49.     mapped_type & operator[](const key_type & k);

    Effects: If there is no key equivalent to k in the flat_map, inserts value_type(k, T()) into the flat_map.

    Returns: A reference to the mapped_type corresponding to k in *this.

    Complexity: Logarithmic search time plus linear insertion time in case no equivalent key is present.

50.     mapped_type & operator[](key_type && k);

    Effects: If there is no key equivalent to k in the flat_map, inserts value_type(move(k), T()) into the flat_map (the key is move-constructed)

    Returns: A reference to the mapped_type corresponding to k in *this.

    Complexity: Logarithmic search time plus linear insertion time in case no equivalent key is present.

51.     template<typename K> mapped_type & operator[](K && k);

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

    Effects: If there is no key equivalent to x in the map, inserts value_type(boost::forward<K>(k), T()) into the map

    Returns: A reference to the mapped_type corresponding to k in *this.

    Complexity: Logarithmic search time plus linear insertion time in case no equivalent key is present

52.     template<typename M>
          std::pair< iterator, bool > insert_or_assign(const key_type & k, M && obj);

    Effects: If a key equivalent to k already exists in the container, assigns forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by insert, constructing it from value_type(k, forward<M>(obj)).

    Returns: The bool component is true if the insertion took place and false if the assignment took place. The iterator component is pointing at the element that was inserted or updated.

    Complexity: Logarithmic search time plus linear insertion time in case no equivalent key is present.

53.     template<typename M>
          std::pair< iterator, bool > insert_or_assign(key_type && k, M && obj);

    Effects: If a key equivalent to k already exists in the container, assigns forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by insert, constructing it from value_type(k, move(obj)).

    Returns: The bool component is true if the insertion took place and false if the assignment took place. The iterator component is pointing at the element that was inserted or updated.

    Complexity: Logarithmic in the size of the container.

54.     template<typename K, typename M>
          std::pair< iterator BOOST_MOVE_I bool > insert_or_assign(K && k, M && obj);

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

    Effects: If a key equivalent to k already exists in the container, assigns forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by insert, constructing it from value_type(k, move(obj)).

    Returns: The bool component is true if the insertion took place and false if the assignment took place. The iterator component is pointing at the element that was inserted or updated.

    Complexity: Logarithmic in the size of the container.

55.     template<typename M>
          iterator insert_or_assign(const_iterator hint, const key_type & k, M && obj);

    Effects: If a key equivalent to k already exists in the container, assigns forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by insert, constructing it from value_type(k, forward<M>(obj)) and the new element to the container as close as possible to the position just before hint.

    Returns: The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic in the size of the container in general, but amortized constant if the new element is inserted just before hint.

56.     template<typename M>
          iterator insert_or_assign(const_iterator hint, key_type && k, M && obj);

    Effects: If a key equivalent to k already exists in the container, assigns forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by insert, constructing it from value_type(k, move(obj)) and the new element to the container as close as possible to the position just before hint.

    Returns: The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic in the size of the container in general, but amortized constant if the new element is inserted just before hint.

57.     template<typename K, typename M>
          iterator insert_or_assign(const_iterator hint, K && k, M && obj);

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

    Effects: If a key equivalent to k already exists in the container, assigns forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by insert, constructing it from value_type(k, move(obj)) and the new element to the container as close as possible to the position just before hint.

    Returns: The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic in the size of the container in general, but amortized constant if the new element is inserted just before hint.

58.     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

59.     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

60.     size_type index_of(iterator p) 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

61.     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

62.     T & at(const key_type & k);

    Returns: A reference to the element whose key is equivalent to x.

    Throws: An exception object of type out_of_range if no such element is present.

    Complexity: logarithmic.

63.     const T & at(const key_type & k) const;

    Returns: A reference to the element whose key is equivalent to x.

    Throws: An exception object of type out_of_range if no such element is present.

    Complexity: logarithmic.

64.     template<typename K> T & at(const K & k);

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

    Returns: A reference to the element whose key is equivalent to x.

    Throws: An exception object of type out_of_range if no such element is present.

    Complexity: logarithmic.

65.     template<typename K> const T & at(const K & k) const;

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

    Returns: A reference to the element whose key is equivalent to x.

    Throws: An exception object of type out_of_range if no such element is present.

    Complexity: logarithmic.

66.     template<class... Args> std::pair< iterator, bool > emplace(Args &&... args);

    Effects: Inserts an object x of type value_type constructed with std::forward<Args>(args)... if and only if there is no element in the container with key equivalent to the key of x.

    Returns: The bool component of the returned pair is true if and only if the insertion takes place, and the iterator component of the pair points to the element with key equivalent to the key of x.

    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.

67.     template<class... Args>
          iterator emplace_hint(const_iterator hint, Args &&... args);

    Effects: Inserts an object of type value_type constructed with std::forward<Args>(args)... in the container if and only if there is no element in the container with key equivalent to the key of x. 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.

68.     template<class... Args>
          std::pair< iterator, bool > try_emplace(const key_type & k, Args &&... args);

    Requires: value_type shall be EmplaceConstructible into map from piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...).

    Effects: If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...).

    Returns: The bool component of the returned pair is true if and only if the insertion took place. The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic.

69.     template<class... Args>
          iterator try_emplace(const_iterator hint, const key_type & k,
                               Args &&... args);

    Requires: value_type shall be EmplaceConstructible into map from piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...).

    Effects: If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(k), forward_as_tuple(forward<Args>(args)...).

    Returns: The returned iterator points to the map element whose key is equivalent to k.

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

70.     template<class... Args>
          std::pair< iterator, bool > try_emplace(key_type && k, Args &&... args);

    Requires: value_type shall be EmplaceConstructible into map from piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Effects: If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Returns: The bool component of the returned pair is true if and only if the insertion took place. The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic search time plus linear insertion time in case the key is not present.

71.     template<class... Args>
          iterator try_emplace(const_iterator hint, key_type && k, Args &&... args);

    Requires: value_type shall be EmplaceConstructible into map from piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Effects: If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Returns: The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic in general, but amortized constant if value is inserted right before p. Linear insertion time in case no equivalent key is present.

72.     template<typename K, class... Args>
          std::pair< iterator BOOST_MOVE_I bool > try_emplace(K && k, Args &&... args);

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

    Requires: value_type shall be EmplaceConstructible into map from piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Effects: If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Returns: The bool component of the returned pair is true if and only if the insertion took place. The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic search time plus linear insertion time in case the key is not present.

73.     template<typename K, class... Args>
          iterator try_emplace(const_iterator hint, K && k, Args &&... args);

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

    Requires: value_type shall be EmplaceConstructible into map from piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Effects: If the map already contains an element whose key is equivalent to k, there is no effect. Otherwise inserts an object of type value_type constructed with piecewise_construct, forward_as_tuple(move(k)), forward_as_tuple(forward<Args>(args)...).

    Returns: The returned iterator points to the map element whose key is equivalent to k.

    Complexity: Logarithmic in general, but amortized constant if value is inserted right before p. Linear insertion time in case no equivalent key is present.

74.     std::pair< iterator, bool > insert(const value_type & x);

    Effects: Inserts x if and only if there is no element in the container with key equivalent to the key of x.

    Returns: The bool component of the returned pair is true if and only if the insertion takes place, and the iterator component of the pair points to the element with key equivalent to the key of x.

    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.

75.     std::pair< iterator, bool > insert(value_type && x);

    Effects: Inserts a new value_type move constructed from the pair if and only if there is no element in the container with key equivalent to the key of x.

    Returns: The bool component of the returned pair is true if and only if the insertion takes place, and the iterator component of the pair points to the element with key equivalent to the key of x.

    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.

76.     template<typename Pair>
          std::pair< iterator BOOST_MOVE_I bool > insert(Pair && x);

    Effects: Inserts a new value_type constructed from the pair if and only if there is no element in the container with key equivalent to the key of x.

    Returns: The bool component of the returned pair is true if and only if the insertion takes place, and the iterator component of the pair points to the element with key equivalent to the key of x.

    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.

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

    Effects: Inserts a copy of x in the container if and only if there is no element in the container with key equivalent to the key of x. 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.

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

    Effects: Inserts an element 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.

79.     template<typename Pair> iterator insert(const_iterator p, Pair && x);

    Effects: Inserts an element 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.

80.     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) if and only if there is no element with key equivalent to the key of that element.

    Complexity: N log(size()+N).

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

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

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

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

    Effects: inserts each element from the range [first,last) if and only if there is no element with key equivalent to the key of that element. This function is more efficient than the normal range creation for ordered ranges.

    Complexity: Linear.

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

    Note: Non-standard extension.

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

    Effects: inserts each element from the range [il.begin(), il.end()) if and only if there is no element with key equivalent to the key of that element.

    Complexity: N log(N).

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

83.     void insert(ordered_unique_range_t, std::initializer_list< value_type > il);

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

    Effects: inserts each element from the range [il.begin(), il.end()) if and only if there is no element with key equivalent to the key of that element. This function is more efficient than the normal range creation for ordered ranges.

    Complexity: Linear.

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

    Note: Non-standard extension.

84.     template<typename C2>
          void merge(flat_map< Key, T, C2, AllocatorOrContainer > & source);

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

    Effects: Move-inserts each element from source into *this a using the comparison object of *this. If there is an element in a with key equivalent to the key of an element from source, then that element is not moved from source.

    Complexity: Linear in this->size() + source.size().

    Note: Invalidates all iterators and references.

85.     template<typename C2>
          void merge(flat_map< Key, T, C2, AllocatorOrContainer > && source);

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

    Effects: Move-inserts each element from source into *this a using the comparison object of *this. If there is an element in a with key equivalent to the key of an element from source, then that element is not moved from source.

    Complexity: Linear in this->size() + source.size().

    Note: Invalidates all iterators and references.

86.     template<typename C2>
          void merge(flat_multimap< Key, T, C2, AllocatorOrContainer > & source);

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

    Effects: Move-inserts each element from source into *this a using the comparison object of *this. If there is an element in a with key equivalent to the key of an element from source, then that element is not moved from source.

    Complexity: Linear in this->size() + source.size().

    Note: Invalidates all iterators and references.

87.     template<typename C2>
          void merge(flat_multimap< Key, T, C2, AllocatorOrContainer > && source);

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

    Effects: Move-inserts each element from source into *this a using the comparison object of *this. If there is an element in a with key equivalent to the key of an element from source, then that element is not moved from source.

    Complexity: Linear in this->size() + source.size().

    Note: Invalidates all iterators and references.

88.     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.

89.     size_type erase(const key_type & x);

    Effects: If present, erases the 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.

90.     template<typename K> size_type erase(K && x);

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

    Effects: If present, erases the elements in the container with key equivalent to x.

    Returns: Returns the number of erased elements.

91.     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.

92.     void swap(flat_map & x);

    Effects: Swaps the contents of *this and x.

    Throws: Nothing.

    Complexity: Constant.

93.     void clear() noexcept;

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

    Postcondition: size() == 0.

    Complexity: linear in size().

94.     key_compare key_comp() const;

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

    Complexity: Constant.

95.     value_compare value_comp() const;

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

    Complexity: Constant.

96.     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.

97.     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.

98.     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.

99.     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.

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

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

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

101.     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)

102.     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()).

103.     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()).

104.     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.

105.     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.

106.     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.

107.     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.

108.     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.

109.     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.

110.     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.

111.     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.

112.     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.

113.     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.

114.     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.

115.     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.

116.     sequence_type extract_sequence();

     Effects: Extracts the internal sequence container.

     Complexity: Same as the move constructor of sequence_type, usually constant.

     Postcondition: this->empty()

     Throws: If secuence_type's move constructor throws

117.     void adopt_sequence(sequence_type && seq);

     Effects: Discards the internally hold sequence container and adopts the one passed externally using the move assignment. Erases non-unique elements.

     Complexity: Assuming O(1) move assignment, O(NlogN) with N = seq.size()

     Throws: If the comparison or the move constructor throws

118.     void adopt_sequence(ordered_unique_range_t, sequence_type && seq);

     Requires: seq shall be ordered according to this->compare() and shall contain unique elements.

     Effects: Discards the internally hold sequence container and adopts the one passed externally using the move assignment.

     Complexity: Assuming O(1) move assignment, O(1)

     Throws: If the move assignment throws

119.     const sequence_type & sequence() const noexcept;

     Effects: Returns a const view of the underlying sequence.

     Complexity: Constant

     Throws: Nothing

### `flat_map` friend functions

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

   Effects: Returns true if x and y are equal

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

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

   Effects: Returns true if x and y are unequal

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

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

   Effects: Returns true if x is less than y

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

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

   Effects: Returns true if x is greater than y

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

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

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

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

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

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

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

7.     void swap(flat_map & x, flat_map & y);

   Effects: x.swap(y)

   Complexity: Constant.