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## Class template flat_set

boost::container::flat_set

## Synopsis

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

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

      // construct/copy/destruct
      explicit flat_set();
      explicit flat_set(const Compare &,
                        const allocator_type & = allocator_type());
      explicit flat_set(const allocator_type &);
      template<typename InputIterator>
        flat_set(InputIterator, InputIterator, const Compare & = Compare(),
                 const allocator_type & = allocator_type());
      template<typename InputIterator>
        flat_set(ordered_unique_range_t, InputIterator, InputIterator,
                 const Compare & = Compare(),
                 const allocator_type & = allocator_type());
      flat_set(std::initializer_list< value_type >, const Compare & = Compare(),
               const allocator_type & = allocator_type());
      flat_set(ordered_unique_range_t, std::initializer_list< value_type >,
               const Compare & = Compare(),
               const allocator_type & = allocator_type());
      flat_set(const flat_set &);
      flat_set(flat_set &&);
      flat_set(const flat_set &, const allocator_type &);
      flat_set(flat_set &&, const allocator_type &);
      flat_set & operator=(const flat_set &);
      flat_set & operator=(flat_set &&) noexcept(allocator_traits_type::propagate_on_container_move_assignment::value));
      flat_set & operator=(std::initializer_list< value_type >);

      // public member functions
      allocator_type get_allocator() const noexcept;
      stored_allocator_type & get_stored_allocator() noexcept;
      const stored_allocator_type & get_stored_allocator() const noexcept;
      iterator begin() noexcept;
      const_iterator begin() const 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();
      template<class... Args> std::pair< iterator, bool > emplace(Args &&...);
      template<class... Args> iterator emplace_hint(const_iterator, Args &&...);
      std::pair< iterator, bool > insert(const value_type &);
      std::pair< iterator, bool > insert(value_type &&);
      iterator insert(const_iterator, const value_type &);
      iterator insert(const_iterator, value_type &&);
      template<typename InputIterator> void insert(InputIterator, InputIterator);
      template<typename InputIterator>
        void insert(ordered_unique_range_t, InputIterator, InputIterator);
      void insert(std::initializer_list< value_type >);
      void insert(ordered_unique_range_t, std::initializer_list< value_type >);
      iterator erase(const_iterator);
      size_type erase(const key_type &);
      iterator erase(const_iterator, const_iterator);
      void swap(flat_set &);
      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;
      size_type count(const key_type &) const;
      iterator lower_bound(const key_type &);
      const_iterator lower_bound(const key_type &) const;
      iterator upper_bound(const key_type &);
      const_iterator upper_bound(const key_type &) const;
      std::pair< const_iterator, const_iterator >
      equal_range(const key_type &) const;
      std::pair< iterator, iterator > equal_range(const key_type &);

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

## Description

flat_set is a Sorted Associative Container that stores objects of type Key. It is also a Unique Associative Container, meaning that no two elements are the same.

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

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

This container provides random-access iterators.

### Template Parameters

1.     typename Key

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

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

   is the comparison functor used to order keys

3.     typename Allocator = std::allocator<Key>

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

### `flat_set` public construct/copy/destruct

1.     explicit flat_set();

   Effects: Default constructs an empty container.

   Complexity: Constant.

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

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

   Complexity: Constant.

3.     explicit flat_set(const allocator_type & a);

   Effects: Constructs an empty container using the specified allocator.

   Complexity: Constant.

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

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

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

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

   Effects: Constructs an empty container using the specified comparison object and allocator, and inserts elements from the 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.

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

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

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

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

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

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

   Complexity: Linear in N.

   Note: Non-standard extension.

8.     flat_set(const flat_set & x);

   Effects: Copy constructs the container.

   Complexity: Linear in x.size().

9.     flat_set(flat_set && mx);

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

   Complexity: Constant.

   Postcondition: mx is emptied.

10.     flat_set(const flat_set & x, const allocator_type & a);

    Effects: Copy constructs a container using the specified allocator.

    Complexity: Linear in x.size().

11.     flat_set(flat_set && mx, const allocator_type & a);

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

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

12.     flat_set & operator=(const flat_set & x);

    Effects: Makes *this a copy of x.

    Complexity: Linear in x.size().

13.     flat_set & operator=(flat_set && x) noexcept(allocator_traits_type::propagate_on_container_move_assignment::value));

    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.

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

    Effects: Copy all elements from il to *this.

    Complexity: Linear in il.size().

### `flat_set` public member functions

1.     allocator_type get_allocator() const noexcept;

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

   Complexity: Constant.

2.     stored_allocator_type & get_stored_allocator() noexcept;

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

3.     const stored_allocator_type & get_stored_allocator() const noexcept;

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

4.     iterator begin() noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

5.     const_iterator begin() const noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

6.     iterator end() noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

7.     const_iterator end() const noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

8.     reverse_iterator rbegin() noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

9.     const_reverse_iterator rbegin() const noexcept;

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

   Throws: Nothing.

   Complexity: Constant.

10.     reverse_iterator rend() noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

11.     const_reverse_iterator rend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

12.     const_iterator cbegin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

13.     const_iterator cend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

14.     const_reverse_iterator crbegin() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

15.     const_reverse_iterator crend() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

16.     bool empty() const noexcept;

    Effects: Returns true if the container contains no elements.

    Throws: Nothing.

    Complexity: Constant.

17.     size_type size() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

18.     size_type max_size() const noexcept;

    Effects: Returns the largest possible size of the container.

    Throws: Nothing.

    Complexity: Constant.

19.     size_type capacity() const noexcept;

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

    Throws: Nothing.

    Complexity: Constant.

20.     void reserve(size_type cnt);

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

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

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

21.     void shrink_to_fit();

    Effects: Tries to deallocate the excess of memory created

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

    Complexity: Linear to size().

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

    Effects: Inserts an object x of type Key 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.

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

    Effects: Inserts an object of type Key constructed with std::forward<Args>(args)... in the container 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.

24.     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.

25.     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.

26.     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.

27.     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.

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

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

    Effects: inserts each element from the range [first,last) 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) search time plus N*size() insertion time.

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

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

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

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

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

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

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

    Effects: inserts each element from the range [il.begin(), il.end()) 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()) search time plus N*size() insertion time.

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

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

    Requires: Range [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()) .This function is more efficient than the normal range creation for ordered ranges.

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

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

32.     iterator erase(const_iterator p);

    Effects: Erases the element pointed to by p.

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

    Complexity: Linear to the elements with keys bigger than p

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

33.     size_type erase(const key_type & x);

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

    Returns: Returns the number of erased elements.

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

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

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

    Returns: Returns last.

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

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

35.     void swap(flat_set & x);

    Effects: Swaps the contents of *this and x.

    Throws: Nothing.

    Complexity: Constant.

36.     void clear() noexcept;

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

    Postcondition: size() == 0.

    Complexity: linear in size().

37.     key_compare key_comp() const;

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

    Complexity: Constant.

38.     value_compare value_comp() const;

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

    Complexity: Constant.

39.     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.

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

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

    Complexity: Logarithmic.

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

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

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

42.     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

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

    Returns: Allocator 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

44.     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

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

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

    Complexity: Logarithmic

46.     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

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

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

    Complexity: Logarithmic

### `flat_set` friend functions

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

   Effects: Returns true if x and y are equal

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

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

   Effects: Returns true if x and y are unequal

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

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

   Effects: Returns true if x is less than y

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

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

   Effects: Returns true if x is greater than y

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

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

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

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

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

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

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

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

   Effects: x.swap(y)

   Complexity: Constant.