26 Containers library [containers]

26.4 Associative containers [associative]

26.4.6 Class template set [set]

26.4.6.1 Class template set overview [set.overview]

A set is an associative container that supports unique keys (contains at most one of each key value) and provides for fast retrieval of the keys themselves.
The set class supports bidirectional iterators.
A set satisfies all of the requirements of a container, of a reversible container, of an associative container, and of an allocator-aware container.
A set also provides most operations described in [associative.reqmts] for unique keys.
This means that a set supports the a_­uniq operations in [associative.reqmts] but not the a_­eq operations.
For a set<Key> both the key_­type and value_­type are Key.
Descriptions are provided here only for operations on set that are not described in one of these tables and for operations where there is additional semantic information.
namespace std {
  template <class Key, class Compare = less<Key>,
            class Allocator = allocator<Key>>
  class set {
  public:
    // types:
    using key_type               = Key;
    using key_compare            = Compare;
    using value_type             = Key;
    using value_compare          = Compare;
    using allocator_type         = Allocator;
    using pointer                = typename allocator_traits<Allocator>::pointer;
    using const_pointer          = typename allocator_traits<Allocator>::const_pointer;
    using reference              = value_type&;
    using const_reference        = const value_type&;
    using size_type              = implementation-defined; // see [container.requirements]
    using difference_type        = implementation-defined; // see [container.requirements]
    using iterator               = implementation-defined; // see [container.requirements]
    using const_iterator         = implementation-defined; // see [container.requirements]
    using reverse_iterator       = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    using node_type              = unspecified;
    using insert_return_type     = INSERT_RETURN_TYPE<iterator, node_type>;

    // [set.cons], construct/copy/destroy
    set() : set(Compare()) { }
    explicit set(const Compare& comp, const Allocator& = Allocator());
    template <class InputIterator>
      set(InputIterator first, InputIterator last,
          const Compare& comp = Compare(), const Allocator& = Allocator());
    set(const set& x);
    set(set&& x);
    explicit set(const Allocator&);
    set(const set&, const Allocator&);
    set(set&&, const Allocator&);
    set(initializer_list<value_type>, const Compare& = Compare(),
        const Allocator& = Allocator());
    template <class InputIterator>
      set(InputIterator first, InputIterator last, const Allocator& a)
        : set(first, last, Compare(), a) { }
    set(initializer_list<value_type> il, const Allocator& a)
      : set(il, Compare(), a) { }
    ~set();
    set& operator=(const set& x);
    set& operator=(set&& x)
      noexcept(allocator_traits<Allocator>::is_always_equal::value &&
               is_nothrow_move_assignable_v<Compare>);
    set& operator=(initializer_list<value_type>);
    allocator_type get_allocator() const noexcept;

    // iterators:
    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;

    // capacity:
    bool      empty() const noexcept;
    size_type size() const noexcept;
    size_type max_size() const noexcept;

    // modifiers:
    template <class... Args> pair<iterator, bool> emplace(Args&&... args);
    template <class... Args> iterator emplace_hint(const_iterator position, Args&&... args);
    pair<iterator,bool> insert(const value_type& x);
    pair<iterator,bool> insert(value_type&& x);
    iterator insert(const_iterator position, const value_type& x);
    iterator insert(const_iterator position, value_type&& x);
    template <class InputIterator>
      void insert(InputIterator first, InputIterator last);
    void insert(initializer_list<value_type>);

    node_type extract(const_iterator position);
    node_type extract(const key_type& x);
    insert_return_type insert(node_type&& nh);
    iterator           insert(const_iterator hint, node_type&& nh);

    iterator  erase(iterator position);
    iterator  erase(const_iterator position);
    size_type erase(const key_type& x);
    iterator  erase(const_iterator first, const_iterator last);
    void      swap(set&)
      noexcept(allocator_traits<Allocator>::is_always_equal::value &&
               is_nothrow_swappable_v<Compare>);
    void      clear() noexcept;

    template<class C2>
      void merge(set<Key, C2, Allocator>& source);
    template<class C2>
      void merge(set<Key, C2, Allocator>&& source);
    template<class C2>
      void merge(multiset<Key, C2, Allocator>& source);
    template<class C2>
      void merge(multiset<Key, C2, Allocator>&& source);

    // observers:
    key_compare key_comp() const;
    value_compare value_comp() const;

    // set operations:
    iterator       find(const key_type& x);
    const_iterator find(const key_type& x) const;
    template <class K> iterator       find(const K& x);
    template <class K> const_iterator find(const K& x) const;

    size_type      count(const key_type& x) const;
    template <class K> size_type count(const K& x) const;

    iterator       lower_bound(const key_type& x);
    const_iterator lower_bound(const key_type& x) const;
    template <class K> iterator       lower_bound(const K& x);
    template <class K> const_iterator lower_bound(const K& x) const;

    iterator       upper_bound(const key_type& x);
    const_iterator upper_bound(const key_type& x) const;
    template <class K> iterator       upper_bound(const K& x);
    template <class K> const_iterator upper_bound(const K& x) const;

    pair<iterator, iterator>               equal_range(const key_type& x);
    pair<const_iterator, const_iterator>   equal_range(const key_type& x) const;
    template <class K>
      pair<iterator, iterator>             equal_range(const K& x);
    template <class K>
      pair<const_iterator, const_iterator> equal_range(const K& x) const;
  };

  template<class InputIterator,
           class Compare = less<typename iterator_traits<InputIterator>::value_type>,
           class Allocator = allocator<typename iterator_traits<InputIterator>::value_type>>
    set(InputIterator, InputIterator,
        Compare = Compare(), Allocator = Allocator())
      -> set<typename iterator_traits<InputIterator>::value_type, Compare, Allocator>;

  template<class Key, class Compare = less<Key>, class Allocator = allocator<Key>>
    set(initializer_list<Key>, Compare = Compare(), Allocator = Allocator())
      -> set<Key, Compare, Allocator>;

  template<class InputIterator, class Allocator>
    set(InputIterator, InputIterator, Allocator)
      -> set<typename iterator_traits<InputIterator>::value_type,
             less<typename iterator_traits<InputIterator>::value_type>, Allocator>;

  template<class Key, class Allocator>
    set(initializer_list<Key>, Allocator) -> set<Key, less<Key>, Allocator>;

  template <class Key, class Compare, class Allocator>
    bool operator==(const set<Key, Compare, Allocator>& x,
                    const set<Key, Compare, Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator< (const set<Key, Compare, Allocator>& x,
                    const set<Key, Compare, Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator!=(const set<Key, Compare, Allocator>& x,
                    const set<Key, Compare, Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator> (const set<Key, Compare, Allocator>& x,
                    const set<Key, Compare, Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator>=(const set<Key, Compare, Allocator>& x,
                    const set<Key, Compare, Allocator>& y);
  template <class Key, class Compare, class Allocator>
    bool operator<=(const set<Key, Compare, Allocator>& x,
                    const set<Key, Compare, Allocator>& y);

  // [set.special], specialized algorithms
  template <class Key, class Compare, class Allocator>
    void swap(set<Key, Compare, Allocator>& x,
              set<Key, Compare, Allocator>& y)
      noexcept(noexcept(x.swap(y)));
}