cppdraft_translate/cppdraft/unord/map/overview.md

[unord.map.overview]

23 Containers library [containers]

23.5 Unordered associative containers [unord]

23.5.3 Class template unordered_map [unord.map]

23.5.3.1 Overview [unord.map.overview]

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An unordered_map is an unordered associative container that supports unique keys (an unordered_map contains at most one of each key value) and that associates values of another typemapped_type with the keys.

The unordered_map class supports forward iterators.

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An unordered_map meets all of the requirements of a container ([container.reqmts]), of an allocator-aware container ([container.alloc.reqmts]), and of an unordered associative container ([unord.req]).

It provides the operations described in the preceding requirements table for unique keys; that is, an unordered_map supports the a_uniq operations in that table, not the a_eq operations.

For an unordered_map<Key, T> the key_type is Key, the mapped_type is T, and the value_type is pair<const Key, T>.

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Subclause [unord.map] only describes operations on unordered_map that are not described in one of the requirement tables, or for which there is additional semantic information.

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The types iterator and const_iterator meet the constexpr iterator requirements ([iterator.requirements.general]).

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namespace std {template<class Key, class T, class Hash = hash, class Pred = equal_to, class Allocator = allocator<pair<const Key, T>>>class unordered_map {public:// typesusing key_type = Key; using mapped_type = T; using value_type = pair<const Key, T>; using hasher = Hash; using key_equal = Pred; using allocator_type = Allocator; using pointer = typename allocator_traits::pointer; using const_pointer = typename allocator_traits::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 local_iterator = implementation-defined; // see [container.requirements]using const_local_iterator = implementation-defined; // see [container.requirements]using node_type = unspecified; using insert_return_type = insert-return-type<iterator, node_type>; // [unord.map.cnstr], construct/copy/destroyconstexpr unordered_map(); constexpr explicit unordered_map(size_type n, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); templateconstexpr unordered_map(InputIterator f, InputIterator l, size_type n = see below, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); template<container-compatible-range<value_type> R>constexpr unordered_map(from_range_t, R&& rg, size_type n = see below, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); constexpr unordered_map(const unordered_map&); constexpr unordered_map(unordered_map&&); constexpr explicit unordered_map(const Allocator&); constexpr unordered_map(const unordered_map&, const type_identity_t&); constexpr unordered_map(unordered_map&&, const type_identity_t&); constexpr unordered_map(initializer_list<value_type> il, size_type n = see below, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); constexpr unordered_map(size_type n, const allocator_type& a): unordered_map(n, hasher(), key_equal(), a) { }constexpr unordered_map(size_type n, const hasher& hf, const allocator_type& a): unordered_map(n, hf, key_equal(), a) { }templateconstexpr unordered_map(InputIterator f, InputIterator l, size_type n, const allocator_type& a): unordered_map(f, l, n, hasher(), key_equal(), a) { }templateconstexpr unordered_map(InputIterator f, InputIterator l, size_type n, const hasher& hf, const allocator_type& a): unordered_map(f, l, n, hf, key_equal(), a) { }template<container-compatible-range<value_type> R>constexpr unordered_map(from_range_t, R&& rg, size_type n, const allocator_type& a): unordered_map(from_range, std::forward(rg), n, hasher(), key_equal(), a) { }template<container-compatible-range<value_type> R>constexpr unordered_map(from_range_t, R&& rg, size_type n, const hasher& hf, const allocator_type& a): unordered_map(from_range, std::forward(rg), n, hf, key_equal(), a) { }constexpr unordered_map(initializer_list<value_type> il, size_type n, const allocator_type& a): unordered_map(il, n, hasher(), key_equal(), a) { }constexpr unordered_map(initializer_list<value_type> il, size_type n, const hasher& hf, const allocator_type& a): unordered_map(il, n, hf, key_equal(), a) { }constexpr ~unordered_map(); constexpr unordered_map& operator=(const unordered_map&); constexpr unordered_map& operator=(unordered_map&&)noexcept(allocator_traits::is_always_equal::value && is_nothrow_move_assignable_v && is_nothrow_move_assignable_v); constexpr unordered_map& operator=(initializer_list<value_type>); constexpr allocator_type get_allocator() const noexcept; // iteratorsconstexpr iterator begin() noexcept; constexpr const_iterator begin() const noexcept; constexpr iterator end() noexcept; constexpr const_iterator end() const noexcept; constexpr const_iterator cbegin() const noexcept; constexpr const_iterator cend() const noexcept; // capacityconstexpr bool empty() const noexcept; constexpr size_type size() const noexcept; constexpr size_type max_size() const noexcept; // [unord.map.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& obj); constexpr pair<iterator, bool> insert(value_type&& obj); template constexpr pair<iterator, bool> insert(P&& obj); constexpr iterator insert(const_iterator hint, const value_type& obj); constexpr iterator insert(const_iterator hint, value_type&& obj); template constexpr iterator insert(const_iterator hint, P&& obj); template constexpr void insert(InputIterator first, InputIterator last); template<container-compatible-range<value_type> R>constexpr void insert_range(R&& rg); constexpr void insert(initializer_list<value_type>); constexpr node_type extract(const_iterator position); constexpr node_type extract(const key_type& x); template constexpr node_type extract(K&& x); constexpr insert_return_type insert(node_type&& nh); constexpr iterator insert(const_iterator hint, node_type&& nh); 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); templateconstexpr pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj); templateconstexpr 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); templateconstexpr iterator insert_or_assign(const_iterator hint, const key_type& k, M&& obj); templateconstexpr 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& k); template constexpr size_type erase(K&& x); constexpr iterator erase(const_iterator first, const_iterator last); constexpr void swap(unordered_map&)noexcept(allocator_traits::is_always_equal::value && is_nothrow_swappable_v && is_nothrow_swappable_v); constexpr void clear() noexcept; template<class H2, class P2>constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>& source); template<class H2, class P2>constexpr void merge(unordered_map<Key, T, H2, P2, Allocator>&& source); template<class H2, class P2>constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>& source); template<class H2, class P2>constexpr void merge(unordered_multimap<Key, T, H2, P2, Allocator>&& source); // observersconstexpr hasher hash_function() const; constexpr key_equal key_eq() const; // map operationsconstexpr iterator find(const key_type& k); constexpr const_iterator find(const key_type& k) const; templateconstexpr iterator find(const K& k); templateconstexpr const_iterator find(const K& k) const; constexpr size_type count(const key_type& k) const; templateconstexpr size_type count(const K& k) const; constexpr bool contains(const key_type& k) const; templateconstexpr bool contains(const K& k) const; constexpr pair<iterator, iterator> equal_range(const key_type& k); constexpr pair<const_iterator, const_iterator> equal_range(const key_type& k) const; templateconstexpr pair<iterator, iterator> equal_range(const K& k); templateconstexpr pair<const_iterator, const_iterator> equal_range(const K& k) const; // [unord.map.elem], element accessconstexpr mapped_type& operator[](const key_type& k); constexpr mapped_type& operator[](key_type&& k); template constexpr mapped_type& operator[](K&& k); constexpr mapped_type& at(const key_type& k); constexpr const mapped_type& at(const key_type& k) const; template constexpr mapped_type& at(const K& k); template constexpr const mapped_type& at(const K& k) const; // bucket interfaceconstexpr size_type bucket_count() const noexcept; constexpr size_type max_bucket_count() const noexcept; constexpr size_type bucket_size(size_type n) const; constexpr size_type bucket(const key_type& k) const; template constexpr size_type bucket(const K& k) const; constexpr local_iterator begin(size_type n); constexpr const_local_iterator begin(size_type n) const; constexpr local_iterator end(size_type n); constexpr const_local_iterator end(size_type n) const; constexpr const_local_iterator cbegin(size_type n) const; constexpr const_local_iterator cend(size_type n) const; // hash policyconstexpr float load_factor() const noexcept; constexpr float max_load_factor() const noexcept; constexpr void max_load_factor(float z); constexpr void rehash(size_type n); constexpr void reserve(size_type n); }; template<class InputIterator, class Hash = hash<iter-key-type>, class Pred = equal_to<iter-key-type>, class Allocator = allocator<iter-to-alloc-type>> unordered_map(InputIterator, InputIterator, typename see below::size_type = see below, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_map<iter-key-type, iter-mapped-type, Hash, Pred, Allocator>; template<ranges::input_range R, class Hash = hash<range-key-type>, class Pred = equal_to<range-key-type>, class Allocator = allocator<range-to-alloc-type>> unordered_map(from_range_t, R&&, typename see below::size_type = see below, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_map<range-key-type, range-mapped-type, Hash, Pred, Allocator>; template<class Key, class T, class Hash = hash, class Pred = equal_to, class Allocator = allocator<pair<const Key, T>>> unordered_map(initializer_list<pair<Key, T>>, typename see below::size_type = see below, Hash = Hash(), Pred = Pred(), Allocator = Allocator())-> unordered_map<Key, T, Hash, Pred, Allocator>; template<class InputIterator, class Allocator> unordered_map(InputIterator, InputIterator, typename see below::size_type, Allocator)-> unordered_map<iter-key-type, iter-mapped-type, hash<iter-key-type>, equal_to<iter-key-type>, Allocator>; template<class InputIterator, class Allocator> unordered_map(InputIterator, InputIterator, Allocator)-> unordered_map<iter-key-type, iter-mapped-type, hash<iter-key-type>, equal_to<iter-key-type>, Allocator>; template<class InputIterator, class Hash, class Allocator> unordered_map(InputIterator, InputIterator, typename see below::size_type, Hash, Allocator)-> unordered_map<iter-key-type, iter-mapped-type, Hash, equal_to<iter-key-type>, Allocator>; template<ranges::input_range R, class Allocator> unordered_map(from_range_t, R&&, typename see below::size_type, Allocator)-> unordered_map<range-key-type, range-mapped-type, hash<range-key-type>, equal_to<range-key-type>, Allocator>; template<ranges::input_range R, class Allocator> unordered_map(from_range_t, R&&, Allocator)-> unordered_map<range-key-type, range-mapped-type, hash<range-key-type>, equal_to<range-key-type>, Allocator>; template<ranges::input_range R, class Hash, class Allocator> unordered_map(from_range_t, R&&, typename see below::size_type, Hash, Allocator)-> unordered_map<range-key-type, range-mapped-type, Hash, equal_to<range-key-type>, Allocator>; template<class Key, class T, class Allocator> unordered_map(initializer_list<pair<Key, T>>, typename see below::size_type, Allocator)-> unordered_map<Key, T, hash, equal_to, Allocator>; template<class Key, class T, class Allocator> unordered_map(initializer_list<pair<Key, T>>, Allocator)-> unordered_map<Key, T, hash, equal_to, Allocator>; template<class Key, class T, class Hash, class Allocator> unordered_map(initializer_list<pair<Key, T>>, typename see below::size_type, Hash, Allocator)-> unordered_map<Key, T, Hash, equal_to, Allocator>;}

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A size_type parameter type in an unordered_map deduction guide refers to the size_type member type of the type deduced by the deduction guide.