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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 >::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;

      // construct/copy/destruct
      explicit flat_set();
      explicit flat_set(const Compare &,
                        const allocator_type & = 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(const flat_set &);
      flat_set(BOOST_RV_REF(flat_set));
      flat_set(const flat_set &, const allocator_type &);
      flat_set(BOOST_RV_REF(flat_set), const allocator_type &);
      flat_set& operator=(BOOST_COPY_ASSIGN_REF(flat_set));
      flat_set& operator=(BOOST_RV_REF(flat_set));

      // public member functions
      typedef BOOST_CONTAINER_IMPDEF(tree_t::stored_allocator_type);
      typedef BOOST_CONTAINER_IMPDEF(tree_t::iterator);
      typedef BOOST_CONTAINER_IMPDEF(tree_t::const_iterator) const;
      typedef BOOST_CONTAINER_IMPDEF(tree_t::reverse_iterator);
      typedef BOOST_CONTAINER_IMPDEF(tree_t::const_reverse_iterator) const;
      allocator_type get_allocator() const;
      stored_allocator_type & get_stored_allocator();
      const stored_allocator_type & get_stored_allocator() const;
      iterator begin();
      const_iterator begin() const;
      iterator end();
      const_iterator end() const;
      reverse_iterator rbegin();
      const_reverse_iterator rbegin() const;
      reverse_iterator rend();
      const_reverse_iterator rend() const;
      const_iterator cbegin() const;
      const_iterator cend() const;
      const_reverse_iterator crbegin() const;
      const_reverse_iterator crend() const;
      bool empty() const;
      size_type size() const;
      size_type max_size() const;
      size_type capacity() const;
      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 &&);
       BOOST_MOVE_CONVERSION_AWARE_CATCH(insert, value_type, insert_return_pair,
                                         this->);
      iterator insert(const_iterator, value_type &&);
       BOOST_MOVE_CONVERSION_AWARE_CATCH_1ARG(insert, value_type, iterator,
                                              this->, const_iterator);
      const_iterator equal_range(const key_type &) const;
      std::pair< iterator, iterator > equal_range(const key_type &);

      // public data members
      const value_type & x;
    };

## Description

flat_set is a Sorted Associative Container that stores objects of type Key. flat_set is a Simple Associative Container, meaning that its value type, as well as its key type, is 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.

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

1.     explicit flat_set();

   Effects: Default constructs an empty `flat_set`.

   Complexity: Constant.

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

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

   Complexity: Constant.

3.     template<typename InputIterator>
         flat_set(InputIterator first, InputIterator last,
                  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 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.

4.     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 `flat_set` 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.

5.     flat_set(const flat_set & x);

   Effects: Copy constructs a set.

   Complexity: Linear in x.size().

6.     flat_set(BOOST_RV_REF(flat_set) mx);

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

   Complexity: Constant.

   Postcondition: x is emptied.

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

   Effects: Copy constructs a set using the specified allocator.

   Complexity: Linear in x.size().

8.     flat_set(BOOST_RV_REF(flat_set) mx, const allocator_type & a);

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

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

9.     flat_set& operator=(BOOST_COPY_ASSIGN_REF(flat_set) x);

   Effects: Makes *this a copy of x.

   Complexity: Linear in x.size().

10.     flat_set& operator=(BOOST_RV_REF(flat_set) mx);

    Effects: Makes *this a copy of the previous value of xx.

    Complexity: Linear in x.size().

### `flat_set` public member functions

1.     typedef BOOST_CONTAINER_IMPDEF(tree_t::stored_allocator_type);

2.     typedef BOOST_CONTAINER_IMPDEF(tree_t::iterator);

3.     typedef BOOST_CONTAINER_IMPDEF(tree_t::const_iterator) const;

4.     typedef BOOST_CONTAINER_IMPDEF(tree_t::reverse_iterator);

5.     typedef BOOST_CONTAINER_IMPDEF(tree_t::const_reverse_iterator) const;

6.     allocator_type get_allocator() const;

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

   Complexity: Constant.

7.     stored_allocator_type & get_stored_allocator();

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

8.     const stored_allocator_type & get_stored_allocator() const;

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

9.     iterator begin();

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

   Throws: Nothing.

   Complexity: Constant.

10.     const_iterator begin() const;

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

    Throws: Nothing.

    Complexity: Constant.

11.     iterator end();

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

    Throws: Nothing.

    Complexity: Constant.

12.     const_iterator end() const;

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

    Throws: Nothing.

    Complexity: Constant.

13.     reverse_iterator rbegin();

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

    Throws: Nothing.

    Complexity: Constant.

14.     const_reverse_iterator rbegin() const;

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

    Throws: Nothing.

    Complexity: Constant.

15.     reverse_iterator rend();

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

    Throws: Nothing.

    Complexity: Constant.

16.     const_reverse_iterator rend() const;

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

    Throws: Nothing.

    Complexity: Constant.

17.     const_iterator cbegin() const;

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

    Throws: Nothing.

    Complexity: Constant.

18.     const_iterator cend() const;

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

    Throws: Nothing.

    Complexity: Constant.

19.     const_reverse_iterator crbegin() const;

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

    Throws: Nothing.

    Complexity: Constant.

20.     const_reverse_iterator crend() const;

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

    Throws: Nothing.

    Complexity: Constant.

21.     bool empty() const;

    Effects: Returns true if the container contains no elements.

    Throws: Nothing.

    Complexity: Constant.

22.     size_type size() const;

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

    Throws: Nothing.

    Complexity: Constant.

23.     size_type max_size() const;

    Effects: Returns the largest possible size of the container.

    Throws: Nothing.

    Complexity: Constant.

24.     size_type capacity() const;

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

    Throws: Nothing.

    Complexity: Constant.

25.     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.

26.     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().

27.     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.

28.     template<class... Args>
          iterator emplace_hint(const_iterator hint, 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.

29.     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.

30.     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.

31.      BOOST_MOVE_CONVERSION_AWARE_CATCH(insert, value_type, insert_return_pair,
                                           this-> priv_insert);

    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.

32.     iterator insert(const_iterator position, 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.

33.      BOOST_MOVE_CONVERSION_AWARE_CATCH_1ARG(insert, value_type, iterator,
                                                this-> priv_insert, const_iterator);

    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.

34.     const_iterator equal_range(const key_type & x) const;

35.     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