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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 Options = 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;
      typedef implementation_defined                                           node_type;
      typedef implementation_defined                                           insert_return_type;

      // construct/copy/destruct
      map() noexcept(container_detail::is_nothrow_default_constructible< Allocator >::value &&container_detail::is_nothrow_default_constructible< Compare >::value));
      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 &&) noexcept(boost::container::container_detail::is_nothrow_move_constructible< Compare >::value));
      map(const map &, const allocator_type &);
      map(map &&, const allocator_type &);
      map & operator=(const map &);
      map & operator=(map &&) noexcept((allocator_traits_type::propagate_on_container_move_assignment::value||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 &&);
      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 M>
        iterator insert_or_assign(const_iterator, const key_type &, M &&);
      template<typename M>
        iterator insert_or_assign(const_iterator, key_type &&, M &&);
      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 >);
      insert_return_type insert(node_type &&);
      insert_return_type insert(const_iterator, node_type &&);
      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 &&...);
      iterator erase(const_iterator) noexcept;
      size_type erase(const key_type &) noexcept;
      iterator erase(const_iterator, const_iterator) noexcept;
      node_type extract(const key_type &);
      node_type extract(const_iterator);
      template<typename C2> void merge(map< Key, T, C2, Allocator, Options > &);
      template<typename C2> void merge(map< Key, T, C2, Allocator, Options > &&);
      template<typename C2>
        void merge(multimap< Key, T, C2, Allocator, Options > &);
      template<typename C2>
        void merge(multimap< Key, T, C2, Allocator, Options > &&);
      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 Options = tree_assoc_defaults

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

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

1.     map() noexcept(container_detail::is_nothrow_default_constructible< Allocator >::value &&container_detail::is_nothrow_default_constructible< Compare >::value));

   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) noexcept(boost::container::container_detail::is_nothrow_move_constructible< Compare >::value));

    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::propagate_on_container_move_assignment::value||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.     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)).

    No iterators or references are invalidated. If the insertion is successful, pointers and references to the element obtained while it is held in the node handle are invalidated, and pointers and references obtained to that element before it was extracted become valid.

    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.

22.     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)).

    No iterators or references are invalidated. If the insertion is successful, pointers and references to the element obtained while it is held in the node handle are invalidated, and pointers and references obtained to that element before it was extracted become valid.

    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.

23.     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.

    No iterators or references are invalidated. If the insertion is successful, pointers and references to the element obtained while it is held in the node handle are invalidated, and pointers and references obtained to that element before it was extracted become valid.

    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 in general, but amortized constant if the new element is inserted just before hint.

24.     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.

    No iterators or references are invalidated. If the insertion is successful, pointers and references to the element obtained while it is held in the node handle are invalidated, and pointers and references obtained to that element before it was extracted become valid.

    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 in general, but amortized constant if the new element is inserted just before hint.

25.     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.

26.     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.

27.     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.

28.     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.

29.     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.

30.     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.

31.     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.

32.     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.

33.     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.

34.     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.

35.     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.

36.     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.

37.     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)

38.     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())

39.     insert_return_type insert(node_type && nh);

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

    Effects: If nh is empty, has no effect. Otherwise, inserts the element owned by nh if and only if there is no element in the container with a key equivalent to nh.key().

    Returns: If nh is empty, insert_return_type.inserted is false, insert_return_type.position is end(), and insert_return_type.node is empty. Otherwise if the insertion took place, insert_return_type.inserted is true, insert_return_type.position points to the inserted element, and insert_return_type.node is empty; if the insertion failed, insert_return_type.inserted is false, insert_return_type.node has the previous value of nh, and insert_return_type.position points to an element with a key equivalent to nh.key().

    Complexity: Logarithmic

40.     insert_return_type insert(const_iterator hint, node_type && nh);

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

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

41.     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.

42.     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.

43.     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.

44.     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.

45.     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.

46.     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.

47.     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

48.     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)

49.     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.

50.     node_type extract(const key_type & k);

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

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

    Complexity: log(a.size()).

51.     node_type extract(const_iterator position);

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

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

    Complexity: Amortized constant.

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

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

    Effects: Attempts to extract each element in source and insert it into 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 extracted from source.

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

    Throws: Nothing unless the comparison object throws.

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

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

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

    Effects: Attempts to extract each element in source and insert it into 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 extracted from source.

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

    Throws: Nothing unless the comparison object throws.

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

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

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

    Effects: Attempts to extract each element in source and insert it into 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 extracted from source.

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

    Throws: Nothing unless the comparison object throws.

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

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

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

    Effects: Attempts to extract each element in source and insert it into 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 extracted from source.

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

    Throws: Nothing unless the comparison object throws.

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

56.     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().

57.     key_compare key_comp() const;

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

    Complexity: Constant.

58.     value_compare value_comp() const;

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

    Complexity: Constant.

59.     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.

60.     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.

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

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

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

62.     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

63.     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

64.     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

65.     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

66.     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

67.     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

68.     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.