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

 

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<iterator>
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<cstdbool> (C++11/17/20*)   <ccomplex> (C++11/17/20*)	<ctgmath> (C++11/17/20*)	<cstdalign> (C++11/17/20*)	<ciso646> (until C++20)

 

This header is part of the containers library.

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

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>
    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>
    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                 = typename KeyContainer::size_type;
    using difference_type           = typename 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
    flat_set() : flat_set(key_compare()) { }
 
    template<class Allocator>
      flat_set(const flat_set&, const Allocator& a);
    template<class Allocator>
      flat_set(flat_set&&, const Allocator& a);
 
    explicit flat_set(container_type cont, const key_compare& comp = key_compare());
    template<class Allocator>
      flat_set(const container_type& cont, const Allocator& a);
    template<class Allocator>
      flat_set(const container_type& cont, const key_compare& comp, const Allocator& a);
 
    flat_set(sorted_unique_t, container_type cont, const key_compare& comp = key_compare())
      : c(std::move(cont)), compare(comp) { }
    template<class Allocator>
      flat_set(sorted_unique_t, const container_type& cont, const Allocator& a);
    template<class Allocator>
      flat_set(sorted_unique_t, const container_type& cont,
               const key_compare& comp, const Allocator& a);
 
    explicit flat_set(const key_compare& comp)
      : c(), compare(comp) { }
    template<class Allocator>
      flat_set(const key_compare& comp, const Allocator& a);
    template<class Allocator>
      explicit flat_set(const Allocator& a);
 
    template<class InputIter>
      flat_set(InputIter first, InputIter last, const key_compare& comp = key_compare())
        : c(), compare(comp)
        { insert(first, last); }
    template<class InputIter, class Allocator>
      flat_set(InputIter first, InputIter last,
               const key_compare& comp, const Allocator& a);
    template<class InputIter, class Allocator>
      flat_set(InputIter first, InputIter last, const Allocator& a);
 
    template<container-compatible-range<value_type> R>
      flat_set(from_range_t fr, R&& rg)
        : flat_set(fr, std::forward<R>(rg), key_compare()) { }
    template<container-compatible-range<value_type> R, class Allocator>
      flat_set(from_range_t, R&& rg, const Allocator& a);
    template<container-compatible-range<value_type> R>
      flat_set(from_range_t, R&& rg, const key_compare& comp)
        : flat_set(comp)
        { insert_range(std::forward<R>(rg)); }
    template<container-compatible-range<value_type> R, class Allocator>
       flat_set(from_range_t, R&& rg, const key_compare& comp, const Allocator& a);
 
    template<class InputIter>
      flat_set(sorted_unique_t, InputIter first, InputIter last,
               const key_compare& comp = key_compare())
        : c(first, last), compare(comp) { }
    template<class InputIter, class Allocator>
      flat_set(sorted_unique_t, InputIter first, InputIter last,
               const key_compare& comp, const Allocator& a);
    template<class InputIter, class Allocator>
      flat_set(sorted_unique_t, InputIter first, InputIter last, const Allocator& a);
 
    flat_set(initializer_list<value_type> il, const key_compare& comp = key_compare())
        : flat_set(il.begin(), il.end(), comp) { }
    template<class Allocator>
      flat_set(initializer_list<value_type> il, const key_compare& comp, const Allocator& a);
    template<class Allocator>
      flat_set(initializer_list<value_type> il, const Allocator& a);
 
    flat_set(sorted_unique_t s, initializer_list<value_type> il,
             const key_compare& comp = key_compare())
        : flat_set(s, il.begin(), il.end(), comp) { }
    template<class Allocator>
      flat_set(sorted_unique_t, initializer_list<value_type> il,
               const key_compare& comp, const Allocator& a);
    template<class Allocator>
      flat_set(sorted_unique_t, initializer_list<value_type> il, const Allocator& a);
 
    flat_set& operator=(initializer_list<value_type>);
 
    // 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)
      { return emplace(x); }
    pair<iterator, bool> insert(value_type&& x)
      { return emplace(std::move(x)); }
    template<class K> pair<iterator, bool> insert(K&& x);
    iterator insert(const_iterator position, const value_type& x)
      { return emplace_hint(position, x); }
    iterator insert(const_iterator position, value_type&& x)
      { return emplace_hint(position, std::move(x)); }
    template<class K> iterator insert(const_iterator hint, K&& x);
 
    template<class InputIter>
      void insert(InputIter first, InputIter last);
    template<class InputIter>
      void insert(sorted_unique_t, InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
      void insert_range(R&& rg);
 
    void insert(initializer_list<value_type> il)
      { insert(il.begin(), il.end()); }
    void insert(sorted_unique_t s, initializer_list<value_type> il)
      { insert(s, il.begin(), il.end()); }
 
    container_type extract() &&;
    void replace(container_type&&);
 
    iterator erase(iterator position);
    iterator erase(const_iterator position);
    size_type erase(const key_type& x);
    template<class K> size_type erase(K&& x);
    iterator erase(const_iterator first, const_iterator last);
 
    void swap(flat_set& y) noexcept;
    void clear() noexcept;
 
    // 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;
 
    bool contains(const key_type& x) const;
    template<class K> bool contains(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;
 
    friend bool operator==(const flat_set& x, const flat_set& y);
 
    friend /*synth-three-way-result*/<value_type>
      operator<=>(const flat_set& x, const flat_set& y);
 
    friend void swap(flat_set& x, flat_set& y) noexcept { 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                 = typename KeyContainer::size_type;
    using difference_type           = typename 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
    flat_multiset() : flat_multiset(key_compare()) { }
 
    template<class Allocator>
      flat_multiset(const flat_multiset&, const Allocator& a);
    template<class Allocator>
      flat_multiset(flat_multiset&&, const Allocator& a);
 
    explicit flat_multiset(container_type cont, const key_compare& comp = key_compare());
    template<class Allocator>
      flat_multiset(const container_type& cont, const Allocator& a);
    template<class Allocator>
      flat_multiset(const container_type& cont, const key_compare& comp, const Allocator& a);
 
    flat_multiset(sorted_equivalent_t, container_type cont,
                  const key_compare& comp = key_compare())
      : c(std::move(cont)), compare(comp) { }
    template<class Allocator>
      flat_multiset(sorted_equivalent_t, const container_type& cont, const Allocator& a);
    template<class Allocator>
      flat_multiset(sorted_equivalent_t, const container_type& cont,
                    const key_compare& comp, const Allocator& a);
 
    explicit flat_multiset(const key_compare& comp)
      : c(), compare(comp) { }
    template<class Allocator>
      flat_multiset(const key_compare& comp, const Allocator& a);
    template<class Allocator>
      explicit flat_multiset(const Allocator& a);
 
    template<class InputIter>
      flat_multiset(InputIter first, InputIter last,
                    const key_compare& comp = key_compare())
        : c(), compare(comp)
        { insert(first, last); }
    template<class InputIter, class Allocator>
      flat_multiset(InputIter first, InputIter last,
                    const key_compare& comp, const Allocator& a);
    template<class InputIter, class Allocator>
      flat_multiset(InputIter first, InputIter last, const Allocator& a);
 
    template<container-compatible-range<value_type> R>
      flat_multiset(from_range_t fr, R&& rg)
        : flat_multiset(fr, std::forward<R>(rg), key_compare()) { }
    template<container-compatible-range<value_type> R, class Allocator>
      flat_multiset(from_range_t, R&& rg, const Allocator& a);
    template<container-compatible-range<value_type> R>
      flat_multiset(from_range_t, R&& rg, const key_compare& comp)
        : flat_multiset(comp)
        { insert_range(std::forward<R>(rg)); }
    template<container-compatible-range<value_type> R, class Allocator>
      flat_multiset(from_range_t, R&& rg, const key_compare& comp, const Allocator& a);
 
    template<class InputIter>
      flat_multiset(sorted_equivalent_t, InputIter first, InputIter last,
                    const key_compare& comp = key_compare())
        : c(first, last), compare(comp) { }
    template<class InputIter, class Allocator>
      flat_multiset(sorted_equivalent_t, InputIter first, InputIter last,
                    const key_compare& comp, const Allocator& a);
    template<class InputIter, class Allocator>
      flat_multiset(sorted_equivalent_t, InputIter first, InputIter last,
                    const Allocator& a);
 
    flat_multiset(initializer_list<value_type> il, const key_compare& comp = key_compare())
      : flat_multiset(il.begin(), il.end(), comp) { }
    template<class Allocator>
      flat_multiset(initializer_list<value_type> il, const key_compare& comp,
                    const Allocator& a);
    template<class Allocator>
      flat_multiset(initializer_list<value_type> il, const Allocator& a);
 
    flat_multiset(sorted_equivalent_t s, initializer_list<value_type> il,
                  const key_compare& comp = key_compare())
        : flat_multiset(s, il.begin(), il.end(), comp) { }
    template<class Allocator>
      flat_multiset(sorted_equivalent_t, initializer_list<value_type> il,
                    const key_compare& comp, const Allocator& a);
    template<class Allocator>
      flat_multiset(sorted_equivalent_t, initializer_list<value_type> il, const Allocator& a);
 
    flat_multiset& operator=(initializer_list<value_type>);
 
    // 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> iterator emplace(Args&&... args);
    template<class... Args>
      iterator emplace_hint(const_iterator position, Args&&... args);
 
    iterator insert(const value_type& x)
      { return emplace(x); }
    iterator insert(value_type&& x)
      { return emplace(std::move(x)); }
    iterator insert(const_iterator position, const value_type& x)
      { return emplace_hint(position, x); }
    iterator insert(const_iterator position, value_type&& x)
      { return emplace_hint(position, std::move(x)); }
 
    template<class InputIter>
      void insert(InputIter first, InputIter last);
    template<class InputIter>
      void insert(sorted_equivalent_t, InputIter first, InputIter last);
    template<container-compatible-range<value_type> R>
      void insert_range(R&& rg);
 
    void insert(initializer_list<value_type> il)
      { insert(il.begin(), il.end()); }
    void insert(sorted_equivalent_t s, initializer_list<value_type> il)
      { insert(s, il.begin(), il.end()); }
 
    container_type extract() &&;
    void replace(container_type&&);
 
    iterator erase(iterator position);
    iterator erase(const_iterator position);
    size_type erase(const key_type& x);
    template<class K> size_type erase(K&& x);
    iterator erase(const_iterator first, const_iterator last);
 
    void swap(flat_multiset& y) noexcept;
    void clear() noexcept;
 
    // 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;
 
    bool contains(const key_type& x) const;
    template<class K> bool contains(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;
 
    friend bool operator==(const flat_multiset& x, const flat_multiset& y);
 
    friend /*synth-three-way-result*/<value_type>
      operator<=>(const flat_multiset& x, const flat_multiset& y);
 
    friend void swap(flat_multiset& x, flat_multiset& y) noexcept
      { 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]