[flat.map.defn]

# 23 Containers library [[containers]](./#containers)

## 23.6 Container adaptors [[container.adaptors]](container.adaptors#flat.map.defn)

### 23.6.8 Class template flat_map [[flat.map]](flat.map#defn)

#### 23.6.8.2 Definition [flat.map.defn]

namespace std {template<class Key, class T, class Compare = less<Key>, class KeyContainer = vector<Key>, class MappedContainer = vector<T>>class flat_map {public:// typesusing key_type = Key; using mapped_type = T; using value_type = pair<key_type, mapped_type>; using key_compare = Compare; using reference = pair<const key_type&, mapped_type&>; using const_reference = pair<const key_type&, const mapped_type&>; using size_type = size_t; using difference_type = ptrdiff_t; using iterator = *implementation-defined*; // see [[container.requirements]](container.requirements "23.2 Requirements")using const_iterator = *implementation-defined*; // see [[container.requirements]](container.requirements "23.2 Requirements")using reverse_iterator = std::reverse_iterator<iterator>; using const_reverse_iterator = std::reverse_iterator<const_iterator>; using key_container_type = KeyContainer; using mapped_container_type = MappedContainer; class value_compare {private: key_compare *comp*; // *exposition only*constexpr value_compare(key_compare c) : *comp*(c) { } // *exposition only*public:constexpr bool operator()(const_reference x, const_reference y) const {return *comp*(x.first, y.first); }}; struct containers { key_container_type keys;
 mapped_container_type values; }; // [[flat.map.cons]](flat.map.cons "23.6.8.3 Constructors"), constructorsconstexpr flat_map() : flat_map(key_compare()) { }constexpr explicit flat_map(const key_compare& comp): *c*(), *compare*(comp) { }constexpr flat_map(key_container_type key_cont, mapped_container_type mapped_cont, const key_compare& comp = key_compare()); constexpr flat_map(sorted_unique_t, key_container_type key_cont,
 mapped_container_type mapped_cont, const key_compare& comp = key_compare()); template<class InputIterator>constexpr flat_map(InputIterator first, InputIterator last, const key_compare& comp = key_compare()): *c*(), *compare*(comp) { insert(first, last); }template<class InputIterator>constexpr flat_map(sorted_unique_t, InputIterator first, InputIterator last, const key_compare& comp = key_compare()): *c*(), *compare*(comp) { insert(sorted_unique, first, last); }template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<value_type> R>constexpr flat_map(from_range_t, R&& rg): flat_map(from_range, std::forward<R>(rg), key_compare()) { }template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<value_type> R>constexpr flat_map(from_range_t, R&& rg, const key_compare& comp): flat_map(comp) { insert_range(std::forward<R>(rg)); }constexpr flat_map(initializer_list<value_type> il, const key_compare& comp = key_compare()): flat_map(il.begin(), il.end(), comp) { }constexpr flat_map(sorted_unique_t, initializer_list<value_type> il, const key_compare& comp = key_compare()): flat_map(sorted_unique, il.begin(), il.end(), comp) { }// [[flat.map.cons.alloc]](flat.map.cons.alloc "23.6.8.4 Constructors with allocators"), constructors with allocatorstemplate<class Alloc>constexpr explicit flat_map(const Alloc& a); template<class Alloc>constexpr flat_map(const key_compare& comp, const Alloc& a); template<class Alloc>constexpr flat_map(const key_container_type& key_cont, const mapped_container_type& mapped_cont, const Alloc& a); template<class Alloc>constexpr flat_map(const key_container_type& key_cont, const mapped_container_type& mapped_cont, const key_compare& comp, const Alloc& a); template<class Alloc>constexpr flat_map(sorted_unique_t, const key_container_type& key_cont, const mapped_container_type& mapped_cont, const Alloc& a); template<class Alloc>constexpr flat_map(sorted_unique_t, const key_container_type& key_cont, const mapped_container_type& mapped_cont, const key_compare& comp, const Alloc& a); template<class Alloc>constexpr flat_map(const flat_map&, const Alloc& a); template<class Alloc>constexpr flat_map(flat_map&&, const Alloc& a); template<class InputIterator, class Alloc>constexpr flat_map(InputIterator first, InputIterator last, const Alloc& a); template<class InputIterator, class Alloc>constexpr flat_map(InputIterator first, InputIterator last, const key_compare& comp, const Alloc& a); template<class InputIterator, class Alloc>constexpr flat_map(sorted_unique_t, InputIterator first, InputIterator last, const Alloc& a); template<class InputIterator, class Alloc>constexpr flat_map(sorted_unique_t, InputIterator first, InputIterator last, const key_compare& comp, const Alloc& a); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<value_type> R, class Alloc>constexpr flat_map(from_range_t, R&& rg, const Alloc& a); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<value_type> R, class Alloc>constexpr flat_map(from_range_t, R&& rg, const key_compare& comp, const Alloc& a); template<class Alloc>constexpr flat_map(initializer_list<value_type> il, const Alloc& a); template<class Alloc>constexpr flat_map(initializer_list<value_type> il, const key_compare& comp, const Alloc& a); template<class Alloc>constexpr flat_map(sorted_unique_t, initializer_list<value_type> il, const Alloc& a); template<class Alloc>constexpr flat_map(sorted_unique_t, initializer_list<value_type> il, const key_compare& comp, const Alloc& a); constexpr flat_map& operator=(initializer_list<value_type>); // iteratorsconstexpr 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; // [[flat.map.capacity]](flat.map.capacity "23.6.8.5 Capacity"), capacityconstexpr bool empty() const noexcept; constexpr size_type size() const noexcept; constexpr size_type max_size() const noexcept; // [[flat.map.access]](flat.map.access "23.6.8.6 Access"), element accessconstexpr mapped_type& operator[](const key_type& x); constexpr mapped_type& operator[](key_type&& x); template<class K> constexpr mapped_type& operator[](K&& x); constexpr mapped_type& at(const key_type& x); constexpr const mapped_type& at(const key_type& x) const; template<class K> constexpr mapped_type& at(const K& x); template<class K> constexpr const mapped_type& at(const K& x) const; // [[flat.map.modifiers]](flat.map.modifiers "23.6.8.7 Modifiers"), modifierstemplate<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)); }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 P> constexpr pair<iterator, bool> insert(P&& x); template<class P>constexpr iterator insert(const_iterator position, P&&); template<class InputIterator>constexpr void insert(InputIterator first, InputIterator last); template<class InputIterator>constexpr void insert(sorted_unique_t, InputIterator first, InputIterator last); template<[*container-compatible-range*](container.intro.reqmts#concept:container-compatible-range "23.2.2.1 Introduction [container.intro.reqmts]")<value_type> R>constexpr void insert_range(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 containers extract() &&; constexpr void replace(key_container_type&& key_cont, mapped_container_type&& mapped_cont); template<class... Args>constexpr pair<iterator, bool> try_emplace(const key_type& k, Args&&... args); template<class... Args>constexpr pair<iterator, bool> try_emplace(key_type&& k, Args&&... args); template<class K, class... Args>constexpr pair<iterator, bool> try_emplace(K&& k, Args&&... args); template<class... Args>constexpr iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args); template<class... Args>constexpr iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args); template<class K, class... Args>constexpr iterator try_emplace(const_iterator hint, K&& k, Args&&... args); template<class M>constexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj); template<class M>constexpr pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj); template<class K, class M>constexpr pair<iterator, bool> insert_or_assign(K&& k, M&& obj); template<class M>constexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj); template<class M>constexpr iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj); template<class K, class M>constexpr iterator insert_or_assign(const_iterator hint, K&& k, M&& obj); constexpr iterator erase(iterator position); 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_map& y) noexcept; constexpr void clear() noexcept; // observersconstexpr key_compare key_comp() const; constexpr value_compare value_comp() const; constexpr const key_container_type& keys() const noexcept { return *c*.keys; }constexpr const mapped_container_type& values() const noexcept { return *c*.values; }// map operationsconstexpr 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_map& x, const flat_map& y); friend constexpr *synth-three-way-result*<value_type>operator<=>(const flat_map& x, const flat_map& y); friend constexpr void swap(flat_map& x, flat_map& y) noexcept{ x.swap(y); }private: containers *c*; // *exposition only* key_compare *compare*; // *exposition only*struct *key-equiv* { // *exposition only*constexpr *key-equiv*(key_compare c) : comp(c) { }constexpr bool operator()(const_reference x, const_reference y) const {return !comp(x.first, y.first) && !comp(y.first, x.first); } key_compare comp; }; }; template<class KeyContainer, class MappedContainer, class Compare = less<typename KeyContainer::value_type>> flat_map(KeyContainer, MappedContainer, Compare = Compare())-> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type,
 Compare, KeyContainer, MappedContainer>; template<class KeyContainer, class MappedContainer, class Allocator> flat_map(KeyContainer, MappedContainer, Allocator)-> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type,
 less<typename KeyContainer::value_type>, KeyContainer, MappedContainer>; template<class KeyContainer, class MappedContainer, class Compare, class Allocator> flat_map(KeyContainer, MappedContainer, Compare, Allocator)-> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type,
 Compare, KeyContainer, MappedContainer>; template<class KeyContainer, class MappedContainer, class Compare = less<typename KeyContainer::value_type>> flat_map(sorted_unique_t, KeyContainer, MappedContainer, Compare = Compare())-> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type,
 Compare, KeyContainer, MappedContainer>; template<class KeyContainer, class MappedContainer, class Allocator> flat_map(sorted_unique_t, KeyContainer, MappedContainer, Allocator)-> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type,
 less<typename KeyContainer::value_type>, KeyContainer, MappedContainer>; template<class KeyContainer, class MappedContainer, class Compare, class Allocator> flat_map(sorted_unique_t, KeyContainer, MappedContainer, Compare, Allocator)-> flat_map<typename KeyContainer::value_type, typename MappedContainer::value_type,
 Compare, KeyContainer, MappedContainer>; template<class InputIterator, class Compare = less<*iter-key-type*<InputIterator>>> flat_map(InputIterator, InputIterator, Compare = Compare())-> flat_map<*iter-key-type*<InputIterator>, *iter-mapped-type*<InputIterator>, Compare>; template<class InputIterator, class Compare = less<*iter-key-type*<InputIterator>>> flat_map(sorted_unique_t, InputIterator, InputIterator, Compare = Compare())-> flat_map<*iter-key-type*<InputIterator>, *iter-mapped-type*<InputIterator>, Compare>; template<ranges::[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Compare = less<*range-key-type*<R>>, class Allocator = allocator<byte>> flat_map(from_range_t, R&&, Compare = Compare(), Allocator = Allocator())-> flat_map<*range-key-type*<R>, *range-mapped-type*<R>, Compare,
 vector<*range-key-type*<R>, *alloc-rebind*<Allocator, *range-key-type*<R>>>,
 vector<*range-mapped-type*<R>, *alloc-rebind*<Allocator, *range-mapped-type*<R>>>>; template<ranges::[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Allocator> flat_map(from_range_t, R&&, Allocator)-> flat_map<*range-key-type*<R>, *range-mapped-type*<R>, less<*range-key-type*<R>>,
 vector<*range-key-type*<R>, *alloc-rebind*<Allocator, *range-key-type*<R>>>,
 vector<*range-mapped-type*<R>, *alloc-rebind*<Allocator, *range-mapped-type*<R>>>>; template<class Key, class T, class Compare = less<Key>> flat_map(initializer_list<pair<Key, T>>, Compare = Compare())-> flat_map<Key, T, Compare>; template<class Key, class T, class Compare = less<Key>> flat_map(sorted_unique_t, initializer_list<pair<Key, T>>, Compare = Compare())-> flat_map<Key, T, Compare>; template<class Key, class T, class Compare, class KeyContainer, class MappedContainer, class Allocator>struct uses_allocator<flat_map<Key, T, Compare, KeyContainer, MappedContainer>, Allocator>: bool_constant<uses_allocator_v<KeyContainer, Allocator> && uses_allocator_v<MappedContainer, Allocator>> { };}

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L17411)

The member type containers has the data members and special members
specified above[.](#1.sentence-1)

It has no base classes or members other than those specified[.](#1.sentence-2)
