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## Class template map

boost::container::map

## 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 MapOptions = tree_assoc_defaults>
    class map {
    public:
      // types
      typedef Key                                                              key_type;
      typedef ::boost::container::allocator_traits< Allocator >                allocator_traits_type;
      typedef T                                                                mapped_type;
      typedef std::pair< const Key, T >                                        value_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                                           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;

      // construct/copy/destruct
      map();
      explicit map(const Compare &, const allocator_type & = allocator_type());
      explicit map(const allocator_type &);
      template<typename InputIterator>
        map(InputIterator, InputIterator, const Compare & = Compare(),
            const allocator_type & = allocator_type());
      template<typename InputIterator>
        map(InputIterator, InputIterator, const allocator_type &);
      template<typename InputIterator>
        map(ordered_unique_range_t, InputIterator, InputIterator,
            const Compare & = Compare(),
            const allocator_type & = allocator_type());
      map(std::initializer_list< value_type >, const Compare & = Compare(),
          const allocator_type & = allocator_type());
      map(std::initializer_list< value_type >, const allocator_type &);
      map(ordered_unique_range_t, std::initializer_list< value_type >,
          const Compare & = Compare(), const allocator_type & = allocator_type());
      map(const map &);
      map(map &&);
      map(const map &, const allocator_type &);
      map(map &&, const allocator_type &);
      map & operator=(const map &);
      map & operator=(map &&) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::container_detail::is_nothrow_move_assignable< Compare >::value));
      map & operator=(std::initializer_list< value_type >);

      // public member functions
      allocator_type get_allocator() const;
      stored_allocator_type & get_stored_allocator() noexcept;
      const stored_allocator_type & get_stored_allocator() const noexcept;
      iterator begin() noexcept;
      const_iterator begin() const noexcept;
      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;
      mapped_type & operator[](const key_type &);
      mapped_type & operator[](key_type &&);
      T & at(const key_type &);
      const T & at(const key_type &) const;
      std::pair< iterator, bool > insert(const value_type &);
      std::pair< iterator, bool > insert(const nonconst_value_type &);
      std::pair< iterator, bool > insert(nonconst_value_type &&);
      std::pair< iterator, bool > insert(movable_value_type &&);
      std::pair< iterator, bool > insert(value_type &&);
      iterator insert(const_iterator, const value_type &);
      iterator insert(const_iterator, nonconst_value_type &&);
      iterator insert(const_iterator, movable_value_type &&);
      iterator insert(const_iterator, const nonconst_value_type &);
      iterator insert(const_iterator, value_type &&);
      template<typename InputIterator> void insert(InputIterator, InputIterator);
      void insert(std::initializer_list< value_type >);
      template<class... Args> std::pair< iterator, bool > emplace(Args &&...);
      template<class... Args> iterator emplace_hint(const_iterator, Args &&...);
      iterator erase(const_iterator) noexcept;
      size_type erase(const key_type &) noexcept;
      iterator erase(const_iterator, const_iterator) noexcept;
      void swap(map &) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::container_detail::is_nothrow_swappable< Compare >::value));
      key_compare key_comp() const;
      value_compare value_comp() const;
      iterator find(const key_type &);
      const_iterator find(const key_type &) const;
      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< iterator, iterator > equal_range(const key_type &);
      std::pair< const_iterator, const_iterator >
      equal_range(const key_type &) const;
      void rebalance();

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

## Description

A 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. The map class supports bidirectional iterators.

A map 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

   is the `mapped_type`

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 MapOptions = tree_assoc_defaults

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

### `map` public construct/copy/destruct

1.     map();

   Effects: Default constructs an empty map.

   Complexity: Constant.

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

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

   Complexity: Constant.

3.     explicit map(const allocator_type & a);

   Effects: Constructs an empty map using the specified allocator.

   Complexity: Constant.

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

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

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

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

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

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

   Complexity: Linear in N.

   Note: Non-standard extension.

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

   Effects: Constructs an empty 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 [first ,last ) is already sorted using comp and otherwise N logN, where N is il.first() - il.end().

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

   Effects: Constructs an empty map 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 comp and otherwise N logN, where N is il.first() - il.end().

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

   Effects: Constructs an empty set 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.     map(const map & x);

    Effects: Copy constructs a map.

    Complexity: Linear in x.size().

11.     map(map && x);

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

    Complexity: Constant.

    Postcondition: x is emptied.

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

    Effects: Copy constructs a map using the specified allocator.

    Complexity: Linear in x.size().

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

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

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

    Postcondition: x is emptied.

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

    Effects: Makes *this a copy of x.

    Complexity: Linear in x.size().

15.     map & operator=(map && x) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::container_detail::is_nothrow_move_assignable< Compare >::value));

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

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

    Effects: Assign content of il to *this.

### `map` public member functions

1.     allocator_type get_allocator() const;

   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 noexcept;

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

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

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

    Complexity: Logarithmic.

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

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

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

    Complexity: Logarithmic.

21.     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.

22.     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.

23.     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.

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

    Effects: Inserts a new value_type created 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.

25.     std::pair< iterator, bool > insert(nonconst_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.

26.     std::pair< iterator, bool > insert(movable_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.

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

    Effects: Move constructs a new value from 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.

28.     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 in general, but amortized constant if t is inserted right before p.

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

    Effects: Move constructs a new value from x 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 in general, but amortized constant if t is inserted right before p.

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

    Effects: Move constructs a new value from x 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 in general, but amortized constant if t is inserted right before p.

31.     iterator insert(const_iterator p, const nonconst_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.

32.     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.

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

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

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

    Effects: Inserts an object x of type T constructed with std::forward<Args>(args)... in the container if and only if there is no element in the container with an equivalent key. p is a hint pointing to where the insert should start to search.

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

36.     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 if and only if there is no element in the container with an equivalent key. 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.

37.     iterator erase(const_iterator p) noexcept;

    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

38.     size_type erase(const key_type & x) noexcept;

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

    Returns: Returns the number of erased elements.

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

39.     iterator erase(const_iterator first, const_iterator last) noexcept;

    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.

40.     void swap(map & x) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::container_detail::is_nothrow_swappable< Compare >::value));

    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().

41.     key_compare key_comp() const;

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

    Complexity: Constant.

42.     value_compare value_comp() const;

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

    Complexity: Constant.

43.     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.

44.     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.

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

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

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

46.     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

47.     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

48.     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

49.     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

50.     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

51.     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

52.     void rebalance();

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

    Complexity: Linear

### `map` friend functions

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

   Effects: x.swap(y)

   Complexity: Constant.