Standard library header <flat_set> (C++23)

This header is part of the containers library.

Includes
<compare> (C++20)	Three-way comparison operator support[edit]
<initializer_list> (C++11)	std::initializer_list class template[edit]
Classes
flat_set (C++23)	adapts a container to provide a collection of unique keys, sorted by keys (class template) [edit]
flat_multiset (C++23)	adapts a container to provide a collection of keys, sorted by keys (class template) [edit]
std::uses_allocator<std::flat_set> (C++23)	specializes the std::uses_allocator type trait (class template specialization) [edit]
std::uses_allocator<std::flat_multiset> (C++23)	specializes the std::uses_allocator type trait (class template specialization) [edit]
Functions
erase_if(std::flat_set) (C++23)	erases all elements satisfying specific criteria (function template) [edit]
erase_if(std::flat_multiset) (C++23)	erases all elements satisfying specific criteria (function template) [edit]
Tags
sorted_uniquesorted_unique_t (C++23)	indicates that elements of a range are sorted and unique (tag)[edit]
sorted_equivalentsorted_equivalent_t (C++23)	indicates that elements of a range are sorted (uniqueness is not required) (tag)[edit]

Synopsis

#include <compare>
#include <initializer_list>

namespace std {
  // class template flat_set
  template<class Key, class Compare = less<Key>, class KeyContainer = vector<Key>>
  class flat_set;

  struct sorted_unique_t
  {
    explicit sorted_unique_t() = default;
  };
  inline constexpr sorted_unique_t sorted_unique{};

  template<class Key, class Compare, class KeyContainer, class Allocator>
  struct uses_allocator<flat_set<Key, Compare, KeyContainer>, Allocator>;

  // erasure for flat_set
  template<class Key, class Compare, class KeyContainer, class Predicate>
  constexpr typename flat_set<Key, Compare, KeyContainer>::size_type erase_if(
    flat_set<Key, Compare, KeyContainer>& c, Predicate pred);

  // class template flat_multiset
  template<class Key, class Compare = less<Key>, class KeyContainer = vector<Key>>
  class flat_multiset;

  struct sorted_equivalent_t
  {
    explicit sorted_equivalent_t() = default;
  };
  inline constexpr sorted_equivalent_t sorted_equivalent{};

  template<class Key, class Compare, class KeyContainer, class Allocator>
  struct uses_allocator<flat_multiset<Key, Compare, KeyContainer>, Allocator>;

  // erasure for flat_multiset
  template<class Key, class Compare, class KeyContainer, class Predicate>
  constexpr typename flat_multiset<Key, Compare, KeyContainer>::size_type erase_if(
    flat_multiset<Key, Compare, KeyContainer>& c, Predicate pred);
}

Class template `std::flat_set`

namespace std {
  template<class Key, class Compare = less<Key>, class KeyContainer = vector<Key>>
  class flat_set
  {
  public:
    // types
    using key_type = Key;
    using value_type = Key;
    using key_compare = Compare;
    using value_compare = Compare;
    using reference = value_type&;
    using const_reference = const value_type&;
    using size_type = KeyContainer::size_type;
    using difference_type = KeyContainer::difference_type;
    using iterator = /* implementation-defined */;
    using const_iterator = /* implementation-defined */;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    using container_type = KeyContainer;

    // constructors
    constexpr flat_set()
      : flat_set(key_compare())
    {
    }

    constexpr flat_set(const flat_set&);
    constexpr flat_set(flat_set&&);
    constexpr flat_set& operator=(const flat_set&);
    constexpr flat_set& operator=(flat_set&&);

    constexpr explicit flat_set(const key_compare& comp)
      : /*c*/()
      , /*compare*/(comp)
    {
    }

    constexpr explicit flat_set(container_type cont,
                                const key_compare& comp = key_compare());

    constexpr flat_set(sorted_unique_t,
                       container_type cont,
                       const key_compare& comp = key_compare())
      : /*c*/(std::move(cont))
      , /*compare*/(comp)
    {
    }

    template<class InputIter>
    constexpr flat_set(InputIter first,
                       InputIter last,
                       const key_compare& comp = key_compare())
      : /*c*/()
      , /*compare*/(comp)
    {
      insert(first, last);
    }

    template<class InputIter>
    constexpr flat_set(sorted_unique_t,
                       InputIter first,
                       InputIter last,
                       const key_compare& comp = key_compare())
      : /*c*/(first, last)
      , /*compare*/(comp)
    {
    }

    template<container-compatible-range<value_type> R>
    constexpr flat_set(from_range_t, R&& rg)
      : flat_set(from_range, std::forward<R>(rg), key_compare())
    {
    }
    template<container-compatible-range<value_type> R>
    constexpr flat_set(from_range_t, R&& rg, const key_compare& comp)
      : flat_set(comp)
    {
      insert_range(std::forward<R>(rg));
    }

    constexpr flat_set(initializer_list<value_type> il,
                       const key_compare& comp = key_compare())
      : flat_set(il.begin(), il.end(), comp)
    {
    }

    constexpr flat_set(sorted_unique_t,
                       initializer_list<value_type> il,
                       const key_compare& comp = key_compare())
      : flat_set(sorted_unique, il.begin(), il.end(), comp)
    {
    }

    // constructors with allocators

    template<class Alloc> constexpr explicit flat_set(const Alloc& a);
    template<class Alloc> constexpr flat_set(const key_compare& comp, const Alloc& a);
    template<class Alloc> constexpr flat_set(const container_type& cont, const Alloc& a);
    template<class Alloc>
    constexpr flat_set(const container_type& cont,
                       const key_compare& comp,
                       const Alloc& a);
    template<class Alloc>
    constexpr flat_set(sorted_unique_t, const container_type& cont, const Alloc& a);
    template<class Alloc>
    constexpr flat_set(sorted_unique_t,
                       const container_type& cont,
                       const key_compare& comp,
                       const Alloc& a);
    template<class Alloc> constexpr flat_set(const flat_set&, const Alloc& a);
    template<class Alloc> constexpr flat_set(flat_set&&, const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_set(InputIter first, InputIter last, const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_set(InputIter first,
                       InputIter last,
                       const key_compare& comp,
                       const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_set(sorted_unique_t, InputIter first, InputIter last, const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_set(sorted_unique_t,
                       InputIter first,
                       InputIter last,
                       const key_compare& comp,
                       const Alloc& a);
    template<container-compatible-range<value_type> R, class Alloc>
    constexpr flat_set(from_range_t, R&& rg, const Alloc& a);
    template<container-compatible-range<value_type> R, class Alloc>
    constexpr flat_set(from_range_t, R&& rg, const key_compare& comp, const Alloc& a);
    template<class Alloc>
    constexpr flat_set(initializer_list<value_type> il, const Alloc& a);
    template<class Alloc>
    constexpr flat_set(initializer_list<value_type> il,
                       const key_compare& comp,
                       const Alloc& a);
    template<class Alloc>
    constexpr flat_set(sorted_unique_t, initializer_list<value_type> il, const Alloc& a);
    template<class Alloc>
    constexpr flat_set(sorted_unique_t,
                       initializer_list<value_type> il,
                       const key_compare& comp,
                       const Alloc& a);

    constexpr flat_set& operator=(initializer_list<value_type>);

    // iterators
    constexpr iterator begin() noexcept;
    constexpr const_iterator begin() const noexcept;
    constexpr iterator end() noexcept;
    constexpr const_iterator end() const noexcept;

    constexpr reverse_iterator rbegin() noexcept;
    constexpr const_reverse_iterator rbegin() const noexcept;
    constexpr reverse_iterator rend() noexcept;
    constexpr const_reverse_iterator rend() const noexcept;

    constexpr const_iterator cbegin() const noexcept;
    constexpr const_iterator cend() const noexcept;
    constexpr const_reverse_iterator crbegin() const noexcept;
    constexpr const_reverse_iterator crend() const noexcept;

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

    // modifiers
    template<class... Args> constexpr pair<iterator, bool> emplace(Args&&... args);
    template<class... Args>
    constexpr iterator emplace_hint(const_iterator position, Args&&... args);

    constexpr pair<iterator, bool> insert(const value_type& x) { return emplace(x); }
    constexpr pair<iterator, bool> insert(value_type&& x)
    {
      return emplace(std::move(x));
    }
    template<class K> constexpr pair<iterator, bool> insert(K&& x);
    constexpr iterator insert(const_iterator position, const value_type& x)
    {
      return emplace_hint(position, x);
    }
    constexpr iterator insert(const_iterator position, value_type&& x)
    {
      return emplace_hint(position, std::move(x));
    }
    template<class K> constexpr iterator insert(const_iterator hint, K&& x);

    template<class InputIter> constexpr void insert(InputIter first, InputIter last);
    template<class InputIter>
    constexpr void insert(sorted_unique_t, InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
    constexpr void insert_range(R&& rg);
    template<container-compatible-range<value_type> R>
    constexpr void insert_range(sorted_unique_t, R&& rg);

    constexpr void insert(initializer_list<value_type> il)
    {
      insert(il.begin(), il.end());
    }
    constexpr void insert(sorted_unique_t, initializer_list<value_type> il)
    {
      insert(sorted_unique, il.begin(), il.end());
    }

    constexpr container_type extract() &&;
    constexpr void replace(container_type&&);

    constexpr iterator erase(iterator position)
      requires(!same_as<iterator, const_iterator>);
    constexpr iterator erase(const_iterator position);
    constexpr size_type erase(const key_type& x);
    template<class K> constexpr size_type erase(K&& x);
    constexpr iterator erase(const_iterator first, const_iterator last);

    constexpr void swap(flat_set& y) noexcept(/* see description */);
    constexpr void clear() noexcept;

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

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

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

    constexpr bool contains(const key_type& x) const;
    template<class K> constexpr bool contains(const K& x) const;

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

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

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

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

    friend constexpr /*synth-three-way-result*/<value_type> operator<=>(
      const flat_set& x, const flat_set& y);

    friend constexpr void swap(flat_set& x, flat_set& y) noexcept(noexcept(x.swap(y)))
    {
      x.swap(y);
    }

  private:
    container_type /*c*/;    // exposition-only
    key_compare /*compare*/; // exposition-only
  };

  template<class KeyContainer, class Compare = less<typename KeyContainer::value_type>>
  flat_set(KeyContainer, Compare = Compare())
    -> flat_set<typename KeyContainer::value_type, Compare, KeyContainer>;
  template<class KeyContainer, class Allocator>
  flat_set(KeyContainer, Allocator) -> flat_set<typename KeyContainer::value_type,
                                                less<typename KeyContainer::value_type>,
                                                KeyContainer>;
  template<class KeyContainer, class Compare, class Allocator>
  flat_set(KeyContainer, Compare, Allocator)
    -> flat_set<typename KeyContainer::value_type, Compare, KeyContainer>;

  template<class KeyContainer, class Compare = less<typename KeyContainer::value_type>>
  flat_set(sorted_unique_t, KeyContainer, Compare = Compare())
    -> flat_set<typename KeyContainer::value_type, Compare, KeyContainer>;
  template<class KeyContainer, class Allocator>
  flat_set(sorted_unique_t, KeyContainer, Allocator)
    -> flat_set<typename KeyContainer::value_type,
                less<typename KeyContainer::value_type>,
                KeyContainer>;
  template<class KeyContainer, class Compare, class Allocator>
  flat_set(sorted_unique_t, KeyContainer, Compare, Allocator)
    -> flat_set<typename KeyContainer::value_type, Compare, KeyContainer>;

  template<class InputIter, class Compare = less</*iter-value-type*/<InputIter>>>
  flat_set(InputIter, InputIter, Compare = Compare())
    -> flat_set</*iter-value-type*/<InputIter>, Compare>;

  template<class InputIter, class Compare = less</*iter-value-type*/<InputIter>>>
  flat_set(sorted_unique_t, InputIter, InputIter, Compare = Compare())
    -> flat_set</*iter-value-type*/<InputIter>, Compare>;

  template<ranges::input_range R,
           class Compare = less<ranges::range_value_t<R>>,
           class Allocator = allocator<ranges::range_value_t<R>>>
  flat_set(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
    -> flat_set<ranges::range_value_t<R>,
                Compare,
                vector<ranges::range_value_t<R>,
                       /*alloc-rebind*/<Allocator, ranges::range_value_t<R>>>>;

  template<ranges::input_range R, class Allocator>
  flat_set(from_range_t, R&&, Allocator)
    -> flat_set<ranges::range_value_t<R>,
                less<ranges::range_value_t<R>>,
                vector<ranges::range_value_t<R>,
                       /*alloc-rebind*/<Allocator, ranges::range_value_t<R>>>>;

  template<class Key, class Compare = less<Key>>
  flat_set(initializer_list<Key>, Compare = Compare()) -> flat_set<Key, Compare>;

  template<class Key, class Compare = less<Key>>
  flat_set(sorted_unique_t, initializer_list<Key>, Compare = Compare())
    -> flat_set<Key, Compare>;

  template<class Key, class Compare, class KeyContainer, class Allocator>
  struct uses_allocator<flat_set<Key, Compare, KeyContainer>, Allocator>
    : bool_constant<uses_allocator_v<KeyContainer, Allocator>>
  {};
}

Class template `std::flat_multiset`

namespace std {
  template<class Key, class Compare = less<Key>, class KeyContainer = vector<Key>>
  class flat_multiset
  {
  public:
    // types
    using key_type = Key;
    using value_type = Key;
    using key_compare = Compare;
    using value_compare = Compare;
    using reference = value_type&;
    using const_reference = const value_type&;
    using size_type = KeyContainer::size_type;
    using difference_type = KeyContainer::difference_type;
    using iterator = /* implementation-defined */;
    using const_iterator = /* implementation-defined */;
    using reverse_iterator = std::reverse_iterator<iterator>;
    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
    using container_type = KeyContainer;

    // constructors
    constexpr flat_multiset()
      : flat_multiset(key_compare())
    {
    }

    constexpr flat_multiset(const flat_multiset&);
    constexpr flat_multiset(flat_multiset&&);
    constexpr flat_multiset& operator=(const flat_multiset&);
    constexpr flat_multiset& operator=(flat_multiset&&);

    constexpr explicit flat_multiset(const key_compare& comp)
      : /*c*/()
      , /*compare*/(comp)
    {
    }

    constexpr explicit flat_multiset(container_type cont,
                                     const key_compare& comp = key_compare());

    constexpr flat_multiset(sorted_equivalent_t,
                            container_type cont,
                            const key_compare& comp = key_compare())
      : /*c*/(std::move(cont))
      , /*compare*/(comp)
    {
    }

    template<class InputIter>
    constexpr flat_multiset(InputIter first,
                            InputIter last,
                            const key_compare& comp = key_compare())
      : /*c*/()
      , /*compare*/(comp)
    {
      insert(first, last);
    }

    template<class InputIter>
    constexpr flat_multiset(sorted_equivalent_t,
                            InputIter first,
                            InputIter last,
                            const key_compare& comp = key_compare())
      : /*c*/(first, last)
      , /*compare*/(comp)
    {
    }

    template<container-compatible-range<value_type> R>
    constexpr flat_multiset(from_range_t, R&& rg)
      : flat_multiset(from_range, std::forward<R>(rg), key_compare())
    {
    }
    template<container-compatible-range<value_type> R>
    constexpr flat_multiset(from_range_t, R&& rg, const key_compare& comp)
      : flat_multiset(comp)
    {
      insert_range(std::forward<R>(rg));
    }

    constexpr flat_multiset(initializer_list<value_type> il,
                            const key_compare& comp = key_compare())
      : flat_multiset(il.begin(), il.end(), comp)
    {
    }

    constexpr flat_multiset(sorted_equivalent_t,
                            initializer_list<value_type> il,
                            const key_compare& comp = key_compare())
      : flat_multiset(sorted_equivalent, il.begin(), il.end(), comp)
    {
    }

    // constructors with allocators

    template<class Alloc> constexpr explicit flat_multiset(const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(const key_compare& comp, const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(const container_type& cont, const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(const container_type& cont,
                            const key_compare& comp,
                            const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(sorted_equivalent_t,
                            const container_type& cont,
                            const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(sorted_equivalent_t,
                            const container_type& cont,
                            const key_compare& comp,
                            const Alloc& a);
    template<class Alloc> constexpr flat_multiset(const flat_multiset&, const Alloc& a);
    template<class Alloc> constexpr flat_multiset(flat_multiset&&, const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_multiset(InputIter first, InputIter last, const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_multiset(InputIter first,
                            InputIter last,
                            const key_compare& comp,
                            const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_multiset(sorted_equivalent_t,
                            InputIter first,
                            InputIter last,
                            const Alloc& a);
    template<class InputIter, class Alloc>
    constexpr flat_multiset(sorted_equivalent_t,
                            InputIter first,
                            InputIter last,
                            const key_compare& comp,
                            const Alloc& a);
    template<container-compatible-range<value_type> R, class Alloc>
    constexpr flat_multiset(from_range_t, R&& rg, const Alloc& a);
    template<container-compatible-range<value_type> R, class Alloc>
    constexpr flat_multiset(from_range_t,
                            R&& rg,
                            const key_compare& comp,
                            const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(initializer_list<value_type> il, const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(initializer_list<value_type> il,
                            const key_compare& comp,
                            const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(sorted_equivalent_t,
                            initializer_list<value_type> il,
                            const Alloc& a);
    template<class Alloc>
    constexpr flat_multiset(sorted_equivalent_t,
                            initializer_list<value_type> il,
                            const key_compare& comp,
                            const Alloc& a);

    constexpr flat_multiset& operator=(initializer_list<value_type>);

    // iterators
    constexpr iterator begin() noexcept;
    constexpr const_iterator begin() const noexcept;
    constexpr iterator end() noexcept;
    constexpr const_iterator end() const noexcept;

    constexpr reverse_iterator rbegin() noexcept;
    constexpr const_reverse_iterator rbegin() const noexcept;
    constexpr reverse_iterator rend() noexcept;
    constexpr const_reverse_iterator rend() const noexcept;

    constexpr const_iterator cbegin() const noexcept;
    constexpr const_iterator cend() const noexcept;
    constexpr const_reverse_iterator crbegin() const noexcept;
    constexpr const_reverse_iterator crend() const noexcept;

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

    // modifiers
    template<class... Args> constexpr iterator emplace(Args&&... args);
    template<class... Args>
    constexpr iterator emplace_hint(const_iterator position, Args&&... args);

    constexpr iterator insert(const value_type& x) { return emplace(x); }
    constexpr iterator insert(value_type&& x) { return emplace(std::move(x)); }
    constexpr iterator insert(const_iterator position, const value_type& x)
    {
      return emplace_hint(position, x);
    }
    constexpr iterator insert(const_iterator position, value_type&& x)
    {
      return emplace_hint(position, std::move(x));
    }

    template<class InputIter> constexpr void insert(InputIter first, InputIter last);
    template<class InputIter>
    constexpr void insert(sorted_equivalent_t, InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
    constexpr void insert_range(R&& rg);
    template<container-compatible-range<value_type> R>
    constexpr void insert_range(sorted_equivalent_t, R&& rg);

    constexpr void insert(initializer_list<value_type> il)
    {
      insert(il.begin(), il.end());
    }
    constexpr void insert(sorted_equivalent_t, initializer_list<value_type> il)
    {
      insert(sorted_equivalent, il.begin(), il.end());
    }

    constexpr container_type extract() &&;
    constexpr void replace(container_type&&);

    constexpr iterator erase(iterator position)
      requires(!same_as<iterator, const_iterator>);
    constexpr iterator erase(const_iterator position);
    constexpr size_type erase(const key_type& x);
    template<class K> constexpr size_type erase(K&& x);
    constexpr iterator erase(const_iterator first, const_iterator last);

    constexpr void swap(flat_multiset& y) noexcept(/* see description */);
    constexpr void clear() noexcept;

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

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

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

    constexpr bool contains(const key_type& x) const;
    template<class K> constexpr bool contains(const K& x) const;

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

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

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

    friend constexpr bool operator==(const flat_multiset& x, const flat_multiset& y);

    friend constexpr /*synth-three-way-result*/<value_type> operator<=>(
      const flat_multiset& x, const flat_multiset& y);

    friend constexpr void swap(flat_multiset& x,
                               flat_multiset& y) noexcept(noexcept(x.swap(y)))
    {
      x.swap(y);
    }

  private:
    container_type /*c*/;    // exposition-only
    key_compare /*compare*/; // exposition-only
  };

  template<class KeyContainer, class Compare = less<typename KeyContainer::value_type>>
  flat_multiset(KeyContainer, Compare = Compare())
    -> flat_multiset<typename KeyContainer::value_type, Compare, KeyContainer>;
  template<class KeyContainer, class Allocator>
  flat_multiset(KeyContainer, Allocator)
    -> flat_multiset<typename KeyContainer::value_type,
                     less<typename KeyContainer::value_type>,
                     KeyContainer>;
  template<class KeyContainer, class Compare, class Allocator>
  flat_multiset(KeyContainer, Compare, Allocator)
    -> flat_multiset<typename KeyContainer::value_type, Compare, KeyContainer>;

  template<class KeyContainer, class Compare = less<typename KeyContainer::value_type>>
  flat_multiset(sorted_equivalent_t, KeyContainer, Compare = Compare())
    -> flat_multiset<typename KeyContainer::value_type, Compare, KeyContainer>;
  template<class KeyContainer, class Allocator>
  flat_multiset(sorted_equivalent_t, KeyContainer, Allocator)
    -> flat_multiset<typename KeyContainer::value_type,
                     less<typename KeyContainer::value_type>,
                     KeyContainer>;
  template<class KeyContainer, class Compare, class Allocator>
  flat_multiset(sorted_equivalent_t, KeyContainer, Compare, Allocator)
    -> flat_multiset<typename KeyContainer::value_type, Compare, KeyContainer>;

  template<class InputIter, class Compare = less</*iter-value-type*/<InputIter>>>
  flat_multiset(InputIter, InputIter, Compare = Compare())
    -> flat_multiset</*iter-value-type*/<InputIter>, Compare>;

  template<class InputIter, class Compare = less</*iter-value-type*/<InputIter>>>
  flat_multiset(sorted_equivalent_t, InputIter, InputIter, Compare = Compare())
    -> flat_multiset</*iter-value-type*/<InputIter>, Compare>;

  template<ranges::input_range R,
           class Compare = less<ranges::range_value_t<R>>,
           class Allocator = allocator<ranges::range_value_t<R>>>
  flat_multiset(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())
    -> flat_multiset<ranges::range_value_t<R>,
                     Compare,
                     vector<ranges::range_value_t<R>,
                            /*alloc-rebind*/<Allocator, ranges::range_value_t<R>>>>;

  template<ranges::input_range R, class Allocator>
  flat_multiset(from_range_t, R&&, Allocator)
    -> flat_multiset<ranges::range_value_t<R>,
                     less<ranges::range_value_t<R>>,
                     vector<ranges::range_value_t<R>,
                            /*alloc-rebind*/<Allocator, ranges::range_value_t<R>>>>;

  template<class Key, class Compare = less<Key>>
  flat_multiset(initializer_list<Key>, Compare = Compare())
    -> flat_multiset<Key, Compare>;

  template<class Key, class Compare = less<Key>>
  flat_multiset(sorted_equivalent_t, initializer_list<Key>, Compare = Compare())
    -> flat_multiset<Key, Compare>;

  template<class Key, class Compare, class KeyContainer, class Allocator>
  struct uses_allocator<flat_multiset<Key, Compare, KeyContainer>, Allocator>
    : bool_constant<uses_allocator_v<KeyContainer, Allocator>>
  {};
}

References

C++23 standard (ISO/IEC 14882:2024):

24.6.5 Header <flat_set> synopsis [flat.set.syn]

24.6.11.2 Definition [flat.set.defn]

24.6.12.2 Definition [flat.multiset.defn]

Standard library header <flat_set> (C++23)

Includes

Classes

Functions

Tags

Synopsis

Class template std::flat_set

Class template std::flat_multiset

References

Class template `std::flat_set`

Class template `std::flat_multiset`