en	Class Template unordered_node_set

en	:idprefix: unordered_node_set_

en	`boost::unordered_node_set` — A node-based, open-addressing unordered associative container that stores unique values.

en	`boost::unordered_node_set` uses an open-addressing layout like `boost::unordered_flat_set`, but, being node-based, it provides pointer stability and node handling functionalities. Its performance lies between those of `boost::unordered_set` and `boost::unordered_flat_set`.

en	As a result of its using open addressing, the interface of `boost::unordered_node_set` deviates in a number of aspects from that of `boost::unordered_set`/`std::unordered_set`:

en	- `begin()` is not constant-time. - There is no API for bucket handling (except `bucket_count`). - The maximum load factor of the container is managed internally and can't be set by the user.

en	Other than this, `boost::unordered_node_set` is mostly a drop-in replacement of standard unordered associative containers.

en	Synopsis

en	---

en	Description

en	*Template Parameters*

en	_Key_

en	`Key` must be https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.

en	_Hash_

en	A unary function object type that acts a hash function for a `Key`. It takes a single argument of type `Key` and returns a value of type `std::size_t`.

en	_Pred_

en	A binary function object that induces an equivalence relation on values of type `Key`. It takes two arguments of type `Key` and returns a value of type `bool`.

en	_Allocator_

en	An allocator whose value type is the same as the container's value type.

en	Allocators using https://en.cppreference.com/w/cpp/named_req/Allocator#Fancy_pointers[fancy pointers] are supported.

en	The element nodes of the container are held into an internal _bucket array_. A node is inserted into a bucket determined by the hash code of its element, but if the bucket is already occupied (a _collision_), an available one in the vicinity of the original position is used.

en	The size of the bucket array can be automatically increased by a call to `insert`/`emplace`, or as a result of calling `rehash`/`reserve`. The _load factor_ of the container (number of elements divided by number of buckets) is never greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to allow for higher loads.

en	If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::value` is `true`, the hash function is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing at the expense of extra computational cost.

en	---

en	Configuration Macros

en	`BOOST_UNORDERED_ENABLE_STATS`

en	Globally define this macro to enable xref:reference/stats.adoc#stats[statistics calculation] for the container. Note that this option decreases the overall performance of many operations.

en	---

en	Typedefs

en	A constant iterator whose value type is `value_type`.

en	The iterator category is at least a forward iterator.

en	Convertible to `const_iterator`.

en	---

en	A constant iterator whose value type is `value_type`.

en	The iterator category is at least a forward iterator.

en	---

en	A class for holding extracted container elements, modelling https://en.cppreference.com/w/cpp/container/node_handle[NodeHandle].

en	---

en	A specialization of an internal class template:

en	with `Iterator` = `iterator` and `NodeType` = `node_type`.

en	---

en	Constructors

en	Default Constructor

en	```c++ unordered_node_set(); ```

en	Constructs an empty container using `hasher()` as the hash function, `key_equal()` as the key equality predicate and `allocator_type()` as the allocator.

en	Postconditions:;; `size() == 0` Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Bucket Count Constructor

en	```c++ explicit unordered_node_set(size_type n, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); ```

en	Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `eql` as the key equality predicate, and `a` as the allocator.

en	Postconditions:;; `size() == 0` Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Iterator Range Constructor

en	Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `eql` as the key equality predicate and `a` as the allocator, and inserts the elements from `[f, l)` into it.

en	Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Copy Constructor

en	```c++ unordered_node_set(unordered_node_set const& other); ```

en	The copy constructor. Copies the contained elements, hash function, predicate and allocator.

en	If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result.

en	Requires:;; `value_type` is copy constructible

en	---

en	Move Constructor

en	```c++ unordered_node_set(unordered_node_set&& other); ```

en	The move constructor. The internal bucket array of `other` is transferred directly to the new container. The hash function, predicate and allocator are moved-constructed from `other`. If statistics are xref:unordered_node_set_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` and calls `other.reset_stats()`.

en	---

en	Iterator Range Constructor with Allocator

en	```c++ template<class InputIterator> unordered_node_set(InputIterator f, InputIterator l, const allocator_type& a); ```

en	Constructs an empty container using `a` as the allocator, with the default hash function and key equality predicate and inserts the elements from `[f, l)` into it.

en	Requires:;; `hasher`, `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Allocator Constructor

en	```c++ explicit unordered_node_set(Allocator const& a); ```

en	Constructs an empty container, using allocator `a`.

en	---

en	Copy Constructor with Allocator

en	```c++ unordered_node_set(unordered_node_set const& other, Allocator const& a); ```

en	Constructs a container, copying ``other``'s contained elements, hash function, and predicate, but using allocator `a`.

en	---

en	Move Constructor with Allocator

en	```c++ unordered_node_set(unordered_node_set&& other, Allocator const& a); ```

en	If `a == other.get_allocator()`, the element nodes of `other` are transferred directly to the new container; otherwise, elements are moved-constructed from those of `other`. The hash function and predicate are moved-constructed from `other`, and the allocator is copy-constructed from `a`. If statistics are xref:unordered_node_set_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` iff `a == other.get_allocator()`, and always calls `other.reset_stats()`.

en	---

en	Move Constructor from concurrent_node_set

en	```c++ unordered_node_set(concurrent_node_set<Key, Hash, Pred, Allocator>&& other); ```

en	Move construction from a xref:#concurrent_node_set[`concurrent_node_set`]. The internal bucket array of `other` is transferred directly to the new container. The hash function, predicate and allocator are moved-constructed from `other`. If statistics are xref:unordered_node_set_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` and calls `other.reset_stats()`.

en	Complexity:;; Constant time. Concurrency:;; Blocking on `other`.

en	---

en	Initializer List Constructor

en	Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `eql` as the key equality predicate and `a`, and inserts the elements from `il` into it.

en	Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Bucket Count Constructor with Allocator

en	```c++ unordered_node_set(size_type n, allocator_type const& a); ```

en	Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default hash function and key equality predicate and `a` as the allocator.

en	Postconditions:;; `size() == 0` Requires:;; `hasher` and `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Bucket Count Constructor with Hasher and Allocator

en	```c++ unordered_node_set(size_type n, hasher const& hf, allocator_type const& a); ```

en	Constructs an empty container with at least `n` buckets, using `hf` as the hash function, the default key equality predicate and `a` as the allocator.

en	Postconditions:;; `size() == 0` Requires:;; `key_equal` needs to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Iterator Range Constructor with Bucket Count and Allocator

en	Constructs an empty container with at least `n` buckets, using `a` as the allocator and default hash function and key equality predicate, and inserts the elements from `[f, l)` into it.

en	Requires:;; `hasher`, `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Iterator Range Constructor with Bucket Count and Hasher

en	Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `a` as the allocator, with the default key equality predicate, and inserts the elements from `[f, l)` into it.

en	Requires:;; `key_equal` needs to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	initializer_list Constructor with Allocator

en	```c++ unordered_node_set(std::initializer_list<value_type> il, const allocator_type& a); ```

en	Constructs an empty container using `a` and default hash function and key equality predicate, and inserts the elements from `il` into it.

en	Requires:;; `hasher` and `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	initializer_list Constructor with Bucket Count and Allocator

en	```c++ unordered_node_set(std::initializer_list<value_type> il, size_type n, const allocator_type& a); ```

en	Constructs an empty container with at least `n` buckets, using `a` and default hash function and key equality predicate, and inserts the elements from `il` into it.

en	Requires:;; `hasher` and `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	initializer_list Constructor with Bucket Count and Hasher and Allocator

en	```c++ unordered_node_set(std::initializer_list<value_type> il, size_type n, const hasher& hf, const allocator_type& a); ```

en	Constructs an empty container with at least `n` buckets, using `hf` as the hash function, `a` as the allocator and default key equality predicate,and inserts the elements from `il` into it.

en	Requires:;; `key_equal` needs to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^].

en	---

en	Destructor

en	```c++ ~unordered_node_set(); ```

en	Note:;; The destructor is applied to every element, and all memory is deallocated

en	---

en	Assignment

en	Copy Assignment

en	```c++ unordered_node_set& operator=(unordered_node_set const& other); ```

en	The assignment operator. Destroys previously existing elements, copy-assigns the hash function and predicate from `other`, copy-assigns the allocator from `other` if `Alloc::propagate_on_container_copy_assignment` exists and `Alloc::propagate_on_container_copy_assignment::value` is `true`, and finally inserts copies of the elements of `other`.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]

en	---

en	Move Assignment

en	```c++ unordered_node_set& operator=(unordered_node_set&& other) noexcept((boost::allocator_traits<Allocator>::is_always_equal::value || boost::allocator_traits<Allocator>::propagate_on_container_move_assignment::value) && std::is_same<pointer, value_type*>::value); ``` The move assignment operator. Destroys previously existing elements, swaps the hash function and predicate from `other`, and move-assigns the allocator from `other` if `Alloc::propagate_on_container_move_assignment` exists and `Alloc::propagate_on_container_move_assignment::value` is `true`. If at this point the allocator is equal to `other.get_allocator()`, the internal bucket array of `other` is transferred directly to the new container; otherwise, inserts move-constructed copies of the elements of `other`. If statistics are xref:unordered_node_set_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` iff the final allocator is equal to `other.get_allocator()`, and always calls `other.reset_stats()`.

en	---

en	Initializer List Assignment

en	```c++ unordered_node_set& operator=(std::initializer_list<value_type> il); ```

en	Assign from values in initializer list. All previously existing elements are destroyed.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]

en	Iterators

en	begin

en	```c++ iterator begin() noexcept; const_iterator begin() const noexcept; ```

en	Returns:;; An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. Complexity:;; O(`bucket_count()`)

en	---

en	end

en	```c++ iterator end() noexcept; const_iterator end() const noexcept; ```

en	Returns:;; An iterator which refers to the past-the-end value for the container.

en	---

en	cbegin

en	```c++ const_iterator cbegin() const noexcept; ```

en	Returns:;; A `const_iterator` referring to the first element of the container, or if the container is empty the past-the-end value for the container. Complexity:;; O(`bucket_count()`)

en	---

en	cend

en	```c++ const_iterator cend() const noexcept; ```

en	Returns:;; A `const_iterator` which refers to the past-the-end value for the container.

en	---

en	Size and Capacity

en	empty

en	```c++ [[nodiscard]] bool empty() const noexcept; ```

en	Returns:;; `size() == 0`

en	---

en	size

en	```c++ size_type size() const noexcept; ```

en	Returns:;; `std::distance(begin(), end())`

en	---

en	max_size

en	```c++ size_type max_size() const noexcept; ```

en	Returns:;; `size()` of the largest possible container.

en	---

en	Modifiers

en	emplace

en	```c++ template<class... Args> std::pair<iterator, bool> emplace(Args&&... args); ```

en	Inserts an object, constructed with the arguments `args`, in the container if and only if there is no element in the container with an equivalent key.

en	Requires:;; `value_type` is constructible from `args`. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load. +

en	---

en	emplace_hint

en	```c++ template<class... Args> iterator emplace_hint(const_iterator position, Args&&... args); ```

en	Inserts an object, constructed with the arguments `args`, in the container if and only if there is no element in the container with an equivalent key.

en	`position` is a suggestion to where the element should be inserted. This implementation ignores it.

en	Requires:;; `value_type` is constructible from `args`. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load. +

en	---

en	Copy Insert

en	```c++ std::pair<iterator, bool> insert(const value_type& obj); ```

en	Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load.

en	---

en	Move Insert

en	```c++ std::pair<iterator, bool> insert(value_type&& obj); ```

en	Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load.

en	---

en	Transparent Insert

en	```c++ template<class K> std::pair<iterator, bool> insert(K&& k); ```

en	Inserts an element constructed from `std::forward<K>(k)` in the container if and only if there is no element in the container with an equivalent key.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^] from `k`. Returns:;; The bool component of the return type is true if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load. + + This overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs and neither `iterator` nor `const_iterator` are implicitly convertible from `K`. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	Copy Insert with Hint

en	```c++ iterator insert(const_iterator hint, const value_type& obj); ``` Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

en	`hint` is a suggestion to where the element should be inserted. This implementation ignores it.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load.

en	---

en	Move Insert with Hint

en	```c++ iterator insert(const_iterator hint, value_type&& obj); ```

en	Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.

en	`hint` is a suggestion to where the element should be inserted. This implementation ignores it.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load.

en	---

en	Transparent Insert with Hint

en	```c++ template<class K> std::pair<iterator, bool> insert(const_iterator hint, K&& k); ```

en	Inserts an element constructed from `std::forward<K>(k)` in the container if and only if there is no element in the container with an equivalent key.

en	`hint` is a suggestion to where the element should be inserted. This implementation ignores it.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^] from `k`. Returns:;; The bool component of the return type is true if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load. + + This overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs and neither `iterator` nor `const_iterator` are implicitly convertible from `K`. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	Insert Iterator Range

en	```c++ template<class InputIterator> void insert(InputIterator first, InputIterator last); ```

en	Inserts a range of elements into the container. Elements are inserted if and only if there is no element in the container with an equivalent key.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^] into the container from `*first`. Throws:;; When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load.

en	---

en	Insert Initializer List

en	```c++ void insert(std::initializer_list<value_type>); ```

en	Inserts a range of elements into the container. Elements are inserted if and only if there is no element in the container with an equivalent key.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^] into the container. Throws:;; When inserting a single element, if an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, but only if the insert causes the load to be greater than the maximum load.

en	---

en	Insert Node

en	```c++ insert_return_type insert(node_type&& nh); ```

en	If `nh` is not empty, inserts the associated element in the container if and only if there is no element in the container with a key equivalent to `nh.value()`. `nh` is empty when the function returns.

en	Returns:;; An `insert_return_type` object constructed from `position`, `inserted` and `node`: +

en	If `nh` is empty, `inserted` is `false`, `position` is `end()`, and `node` is empty.

en	Otherwise if the insertion took place, `inserted` is true, `position` points to the inserted element, and `node` is empty.

en	If the insertion failed, `inserted` is false, `node` has the previous value of `nh`, and `position` points to an element with a key equivalent to `nh.value()`.

en	Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Behavior is undefined if `nh` is not empty and the allocators of `nh` and the container are not equal.

en	---

en	Insert Node with Hint

en	```c++ iterator insert(const_iterator hint, node_type&& nh); ```

en	If `nh` is not empty, inserts the associated element in the container if and only if there is no element in the container with a key equivalent to `nh.value()`. `nh` becomes empty if insertion took place, otherwise it is not changed.

en	`hint` is a suggestion to where the element should be inserted. This implementation ignores it.

en	Returns:;; The iterator returned is `end()` if `nh` is empty. If insertion took place, then the iterator points to the newly inserted element; otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Behavior is undefined if `nh` is not empty and the allocators of `nh` and the container are not equal.

en	---

en	Erase by Position

en	Erase the element pointed to by `position`.

en	Returns:;; An opaque object implicitly convertible to the `iterator` or `const_iterator` immediately following `position` prior to the erasure. Throws:;; Nothing. Notes:;; The opaque object returned must only be discarded or immediately converted to `iterator` or `const_iterator`.

en	---

en	Erase by Key

en	```c++ size_type erase(const key_type& k); template<class K> size_type erase(K&& k); ```

en	Erase all elements with key equivalent to `k`.

en	Returns:;; The number of elements erased. Throws:;; Only throws an exception if it is thrown by `hasher` or `key_equal`. Notes:;; The `template<class K>` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs and neither `iterator` nor `const_iterator` are implicitly convertible from `K`. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	Erase Range

en	```c++ iterator erase(const_iterator first, const_iterator last); ```

en	Erases the elements in the range from `first` to `last`.

en	Returns:;; The iterator following the erased elements - i.e. `last`. Throws:;; Nothing in this implementation (neither the `hasher` nor the `key_equal` objects are called).

en	---

en	swap

en	```c++ void swap(unordered_node_set& other) noexcept(boost::allocator_traits<Allocator>::is_always_equal::value || boost::allocator_traits<Allocator>::propagate_on_container_swap::value); ```

en	Swaps the contents of the container with the parameter.

en	If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is `true` then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

en	Throws:;; Nothing unless `key_equal` or `hasher` throw on swapping.

en	---

en	Extract by Position

en	```c++ node_type extract(const_iterator position); ```

en	Extracts the element pointed to by `position`.

en	Returns:;; A `node_type` object holding the extracted element. Throws:;; Nothing.

en	---

en	Extract by Key

en	```c++ node_type extract(const key_type& k); template<class K> node_type extract(K&& k); ```

en	Extracts the element with key equivalent to `k`, if it exists.

en	Returns:;; A `node_type` object holding the extracted element, or empty if no element was extracted. Throws:;; Only throws an exception if it is thrown by `hasher` or `key_equal`. Notes:;; The `template<class K>` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	pull

en	```c++ init_type pull(const_iterator position); ```

en	Move-constructs an `init_value` `x` from the element pointed to by `position`, erases the element and returns `x`.

en	---

en	clear

en	```c++ void clear() noexcept; ```

en	Erases all elements in the container.

en	Postconditions:;; `size() == 0`, `max_load() >= max_load_factor() * bucket_count()`

en	---

en	merge

en	```c++ template<class H2, class P2> void merge(unordered_node_set<Key, T, H2, P2, Allocator>& source); template<class H2, class P2> void merge(unordered_node_set<Key, T, H2, P2, Allocator>&& source); ```

en	Transfers all the element nodes from `source` whose key is not already present in `*this`.

en	Requires:;; `this\->get_allocator() == source.get_allocator()`. Notes:;; Invalidates iterators to the elements transferred. If the resulting size of `*this` is greater than its original maximum load, invalidates all iterators associated to `*this`.

en	---

en	Observers

en	get_allocator

en	``` allocator_type get_allocator() const noexcept; ```

en	Returns:;; The container's allocator.

en	---

en	hash_function

en	``` hasher hash_function() const; ```

en	Returns:;; The container's hash function.

en	---

en	key_eq

en	``` key_equal key_eq() const; ```

en	Returns:;; The container's key equality predicate

en	---

en	Lookup

en	find

en	```c++ iterator find(const key_type& k); const_iterator find(const key_type& k) const; template<class K> iterator find(const K& k);

en	```

en	Returns:;; An iterator pointing to an element with key equivalent to `k`, or `end()` if no such element exists. Notes:;; The `template<class K>` overloads only participate in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	count

en	```c++ size_type count(const key_type& k) const; template<class K> size_type count(const K& k) const; ```

en	Returns:;; The number of elements with key equivalent to `k`. Notes:;; The `template<class K>` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	contains

en	```c++ bool contains(const key_type& k) const; template<class K> bool contains(const K& k) const; ```

en	Returns:;; A boolean indicating whether or not there is an element with key equal to `key` in the container Notes:;; The `template<class K>` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	equal_range

en	```c++ std::pair<iterator, iterator> equal_range(const key_type& k); std::pair<const_iterator, const_iterator> equal_range(const key_type& k) const; template<class K> std::pair<iterator, iterator> equal_range(const K& k); template<class K> std::pair<const_iterator, const_iterator> equal_range(const K& k) const; ```

en	Returns:;; A range containing all elements with key equivalent to `k`. If the container doesn't contain any such elements, returns `std::make_pair(b.end(), b.end())`. Notes:;; The `template<class K>` overloads only participate in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.

en	---

en	Bucket Interface

en	bucket_count

en	```c++ size_type bucket_count() const noexcept; ```

en	Returns:;; The size of the bucket array.

en	---

en	Hash Policy

en	load_factor

en	```c++ float load_factor() const noexcept; ```

en	Returns:;; `static_cast<float>(size())/static_cast<float>(bucket_count())`, or `0` if `bucket_count() == 0`.

en	---

en	max_load_factor

en	```c++ float max_load_factor() const noexcept; ```

en	Returns:;; Returns the container's maximum load factor.

en	---

en	Set max_load_factor

en	```c++ void max_load_factor(float z); ```

en	Effects:;; Does nothing, as the user is not allowed to change this parameter. Kept for compatibility with `boost::unordered_set`.

en	---

en	max_load

en	```c++ size_type max_load() const noexcept; ```

en	Returns:;; The maximum number of elements the container can hold without rehashing, assuming that no further elements will be erased. Note:;; After construction, rehash or clearance, the container's maximum load is at least `max_load_factor() * bucket_count()`. This number may decrease on erasure under high-load conditions.

en	---

en	rehash

en	```c++ void rehash(size_type n); ```

en	Changes if necessary the size of the bucket array so that there are at least `n` buckets, and so that the load factor is less than or equal to the maximum load factor. When applicable, this will either grow or shrink the `bucket_count()` associated with the container.

en	When `size() == 0`, `rehash(0)` will deallocate the underlying buckets array. If the provided Allocator uses fancy pointers, a default allocation is subsequently performed.

en	Invalidates iterators and changes the order of elements.

en	Throws:;; The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

en	---

en	reserve

en	```c++ void reserve(size_type n); ```

en	Equivalent to `a.rehash(ceil(n / a.max_load_factor()))`.

en	Similar to `rehash`, this function can be used to grow or shrink the number of buckets in the container.

en	Invalidates iterators and changes the order of elements.

en	Throws:;; The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function.

en	---

en	Statistics

en	get_stats

en	```c++ stats get_stats() const; ```

en	Returns:;; A statistical description of the insertion and lookup operations performed by the container so far. Notes:;; Only available if xref:reference/stats.adoc#stats[statistics calculation] is xref:unordered_node_set_boost_unordered_enable_stats[enabled].

en	---

en	reset_stats

en	```c++ void reset_stats() noexcept; ```

en	Effects:;; Sets to zero the internal statistics kept by the container. Notes:;; Only available if xref:reference/stats.adoc#stats[statistics calculation] is xref:unordered_node_set_boost_unordered_enable_stats[enabled].

en	---

en	Deduction Guides

en	A deduction guide will not participate in overload resolution if any of the following are true:

en	- It has an `InputIterator` template parameter and a type that does not qualify as an input iterator is deduced for that parameter. - It has an `Allocator` template parameter and a type that does not qualify as an allocator is deduced for that parameter. - It has a `Hash` template parameter and an integral type or a type that qualifies as an allocator is deduced for that parameter. - It has a `Pred` template parameter and a type that qualifies as an allocator is deduced for that parameter.

en	A `size_­type` parameter type in a deduction guide refers to the `size_­type` member type of the container type deduced by the deduction guide. Its default value coincides with the default value of the constructor selected.

en	__iter-value-type__

en	Equality Comparisons

en	operator

en	```c++ template<class Key, class T, class Hash, class Pred, class Alloc> bool operator==(const unordered_node_set<Key, T, Hash, Pred, Alloc>& x, const unordered_node_set<Key, T, Hash, Pred, Alloc>& y); ```

en	Return `true` if `x.size() == y.size()` and for every element in `x`, there is an element in `y` with the same key, with an equal value (using `operator==` to compare the value types).

en	Notes:;; Behavior is undefined if the two containers don't have equivalent equality predicates.

en	---

en	operator!

en	```c++ template<class Key, class T, class Hash, class Pred, class Alloc> bool operator!=(const unordered_node_set<Key, T, Hash, Pred, Alloc>& x, const unordered_node_set<Key, T, Hash, Pred, Alloc>& y); ```

en	Return `false` if `x.size() == y.size()` and for every element in `x`, there is an element in `y` with the same key, with an equal value (using `operator==` to compare the value types).

en	Notes:;; Behavior is undefined if the two containers don't have equivalent equality predicates.

en	Swap

en	```c++ template<class Key, class T, class Hash, class Pred, class Alloc> void swap(unordered_node_set<Key, T, Hash, Pred, Alloc>& x, unordered_node_set<Key, T, Hash, Pred, Alloc>& y) noexcept(noexcept(x.swap(y))); ```

en	Swaps the contents of `x` and `y`.

en	If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is `true` then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.

en	Effects:;; `x.swap(y)` Throws:;; Nothing unless `key_equal` or `hasher` throw on swapping.

en	---

en	erase_if

en	```c++ template<class K, class T, class H, class P, class A, class Predicate> typename unordered_node_set<K, T, H, P, A>::size_type erase_if(unordered_node_set<K, T, H, P, A>& c, Predicate pred); ```

en	Traverses the container `c` and removes all elements for which the supplied predicate returns `true`.

en	Returns:;; The number of erased elements. Notes:;; Equivalent to: + + ```c++ auto original_size = c.size(); for (auto i = c.begin(), last = c.end(); i != last; ) { if (pred(*i)) { i = c.erase(i); } else { ++i; } } return original_size - c.size(); ```

en	Serialization

en	``unordered_node_set``s can be archived/retrieved by means of link:../../../../../serialization/index.html[Boost.Serialization^] using the API provided by this library. Both regular and XML archives are supported.

en	Saving an unordered_node_set to an archive

en	Saves all the elements of an `unordered_node_set` `x` to an archive (XML archive) `ar`.

en	Requires:;; `value_type` is serializable (XML serializable), and it supports Boost.Serialization `save_construct_data`/`load_construct_data` protocol (automatically suported by https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^] types).

en	---

en	Loading an unordered_node_set from an archive

en	Deletes all preexisting elements of an `unordered_node_set` `x` and inserts from an archive (XML archive) `ar` restored copies of the elements of the original `unordered_node_set` `other` saved to the storage read by `ar`.

en	Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. `x.key_equal()` is functionally equivalent to `other.key_equal()`.

en	---

en	Saving an iterator/const_iterator to an archive

en	Saves the positional information of an `iterator` (`const_iterator`) `it` to an archive (XML archive) `ar`. `it` can be and `end()` iterator.

en	Requires:;; The `unordered_node_set` `x` pointed to by `it` has been previously saved to `ar`, and no modifying operations have been issued on `x` between saving of `x` and saving of `it`.

en	---

en	Loading an iterator/const_iterator from an archive

en	Makes an `iterator` (`const_iterator`) `it` point to the restored position of the original `iterator` (`const_iterator`) saved to the storage read by an archive (XML archive) `ar`.

en	Requires:;; If `x` is the `unordered_node_set` `it` points to, no modifying operations have been issued on `x` between loading of `x` and loading of `it`.