Class Template unordered_node_set

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

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.

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:

  • 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.

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

Synopsis

// #include <boost/unordered/unordered_node_set.hpp>

namespace boost {
namespace unordered {

  template<class Key,
           class Hash = boost::hash<Key>,
           class Pred = std::equal_to<Key>,
           class Allocator = std::allocator<Key>>
  class unordered_node_set {
  public:
    // types
    using key_type             = Key;
    using value_type           = Key;
    using init_type            = Key;
    using hasher               = Hash;
    using key_equal            = Pred;
    using allocator_type       = Allocator;
    using pointer              = typename std::allocator_traits<Allocator>::pointer;
    using const_pointer        = typename std::allocator_traits<Allocator>::const_pointer;
    using reference            = value_type&;
    using const_reference      = const value_type&;
    using size_type            = std::size_t;
    using difference_type      = std::ptrdiff_t;

    using iterator             = implementation-defined;
    using const_iterator       = implementation-defined;

    using node_type            = implementation-defined;
    using insert_return_type   = implementation-defined;

    using stats                = stats-type; // if statistics are enabled

    // construct/copy/destroy
    unordered_node_set();
    explicit unordered_node_set(size_type n,
                                const hasher& hf = hasher(),
                                const key_equal& eql = key_equal(),
                                const allocator_type& a = allocator_type());
    template<class InputIterator>
      unordered_node_set(InputIterator f, InputIterator l,
                         size_type n = implementation-defined,
                         const hasher& hf = hasher(),
                         const key_equal& eql = key_equal(),
                         const allocator_type& a = allocator_type());
    unordered_node_set(const unordered_node_set& other);
    unordered_node_set(unordered_node_set&& other);
    template<class InputIterator>
      unordered_node_set(InputIterator f, InputIterator l, const allocator_type& a);
    explicit unordered_node_set(const Allocator& a);
    unordered_node_set(const unordered_node_set& other, const Allocator& a);
    unordered_node_set(unordered_node_set&& other, const Allocator& a);
    unordered_node_set(concurrent_node_set<Key, Hash, Pred, Allocator>&& other);
    unordered_node_set(std::initializer_list<value_type> il,
                       size_type n = implementation-defined
                       const hasher& hf = hasher(),
                       const key_equal& eql = key_equal(),
                       const allocator_type& a = allocator_type());
    unordered_node_set(size_type n, const allocator_type& a);
    unordered_node_set(size_type n, const hasher& hf, const allocator_type& a);
    template<class InputIterator>
      unordered_node_set(InputIterator f, InputIterator l, size_type n, const allocator_type& a);
    template<class InputIterator>
      unordered_node_set(InputIterator f, InputIterator l, size_type n, const hasher& hf,
                         const allocator_type& a);
    unordered_node_set(std::initializer_list<value_type> il, const allocator_type& a);
    unordered_node_set(std::initializer_list<value_type> il, size_type n,
                       const allocator_type& a);
    unordered_node_set(std::initializer_list<value_type> il, size_type n, const hasher& hf,
                       const allocator_type& a);
    ~unordered_node_set();
    unordered_node_set& operator=(const unordered_node_set& other);
    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);
    unordered_node_set& operator=(std::initializer_list<value_type>);
    allocator_type get_allocator() const noexcept;

    // iterators
    iterator       begin() noexcept;
    const_iterator begin() const noexcept;
    iterator       end() noexcept;
    const_iterator end() const noexcept;
    const_iterator cbegin() const noexcept;
    const_iterator cend() const noexcept;

    // capacity
    [[nodiscard]] bool empty() const noexcept;
    size_type size() const noexcept;
    size_type max_size() const noexcept;

    // modifiers
    template<class... Args> std::pair<iterator, bool> emplace(Args&&... args);
    template<class... Args> iterator emplace_hint(const_iterator position, Args&&... args);
    std::pair<iterator, bool> insert(const value_type& obj);
    std::pair<iterator, bool> insert(value_type&& obj);
    template<class K> std::pair<iterator, bool> insert(K&& k);
    iterator insert(const_iterator hint, const value_type& obj);
    iterator insert(const_iterator hint, value_type&& obj);
    template<class K> iterator insert(const_iterator hint, K&& k);
    template<class InputIterator> void insert(InputIterator first, InputIterator last);
    void insert(std::initializer_list<value_type>);
    insert_return_type insert(node_type&& nh);
    iterator insert(const_iterator hint, node_type&& nh);

    convertible-to-iterator     erase(iterator position);
    convertible-to-iterator     erase(const_iterator position);
    size_type                   erase(const key_type& k);
    template<class K> size_type erase(K&& k);
    iterator  erase(const_iterator first, const_iterator last);
    void      swap(unordered_node_set& other)
      noexcept(boost::allocator_traits<Allocator>::is_always_equal::value ||
               boost::allocator_traits<Allocator>::propagate_on_container_swap::value);
    node_type extract(const_iterator position);
    node_type extract(const key_type& key);
    template<class K> node_type extract(K&& key);
    void      clear() noexcept;

    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);

    // observers
    hasher hash_function() const;
    key_equal key_eq() const;

    // set operations
    iterator         find(const key_type& k);
    const_iterator   find(const key_type& k) const;
    template<class K>
      iterator       find(const K& k);
    template<class K>
      const_iterator find(const K& k) const;
    size_type        count(const key_type& k) const;
    template<class K>
      size_type      count(const K& k) const;
    bool             contains(const key_type& k) const;
    template<class K>
      bool           contains(const K& k) const;
    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;

    // bucket interface
    size_type bucket_count() const noexcept;

    // hash policy
    float load_factor() const noexcept;
    float max_load_factor() const noexcept;
    void max_load_factor(float z);
    size_type max_load() const noexcept;
    void rehash(size_type n);
    void reserve(size_type n);

    // statistics (if enabled)
    stats get_stats() const;
    void reset_stats() noexcept;
  };

  // Deduction Guides
  template<class InputIterator,
           class Hash = boost::hash<iter-value-type<InputIterator>>,
           class Pred = std::equal_to<iter-value-type<InputIterator>>,
           class Allocator = std::allocator<iter-value-type<InputIterator>>>
    unordered_node_set(InputIterator, InputIterator, typename see below::size_type = see below,
                       Hash = Hash(), Pred = Pred(), Allocator = Allocator())
      -> unordered_node_set<iter-value-type<InputIterator>, Hash, Pred, Allocator>;

  template<class T, class Hash = boost::hash<T>, class Pred = std::equal_to<T>,
           class Allocator = std::allocator<T>>
    unordered_node_set(std::initializer_list<T>, typename see below::size_type = see below,
                       Hash = Hash(), Pred = Pred(), Allocator = Allocator())
      -> unordered_node_set<T, Hash, Pred, Allocator>;

  template<class InputIterator, class Allocator>
    unordered_node_set(InputIterator, InputIterator, typename see below::size_type, Allocator)
      -> unordered_node_set<iter-value-type<InputIterator>,
                            boost::hash<iter-value-type<InputIterator>>,
                            std::equal_to<iter-value-type<InputIterator>>, Allocator>;

  template<class InputIterator, class Allocator>
    unordered_node_set(InputIterator, InputIterator, Allocator)
      -> unordered_node_set<iter-value-type<InputIterator>,
                            boost::hash<iter-value-type<InputIterator>>,
                            std::equal_to<iter-value-type<InputIterator>>, Allocator>;

  template<class InputIterator, class Hash, class Allocator>
    unordered_node_set(InputIterator, InputIterator, typename see below::size_type, Hash,
                       Allocator)
      -> unordered_node_set<iter-value-type<InputIterator>, Hash,
                            std::equal_to<iter-value-type<InputIterator>>, Allocator>;

  template<class T, class Allocator>
    unordered_node_set(std::initializer_list<T>, typename see below::size_type, Allocator)
      -> unordered_node_set<T, boost::hash<T>, std::equal_to<T>, Allocator>;

  template<class T, class Allocator>
    unordered_node_set(std::initializer_list<T>, Allocator)
      -> unordered_node_set<T, boost::hash<T>, std::equal_to<T>, Allocator>;

  template<class T, class Hash, class Allocator>
    unordered_node_set(std::initializer_list<T>, typename see below::size_type, Hash, Allocator)
      -> unordered_node_set<T, Hash, std::equal_to<T>, Allocator>;

} // namespace unordered
} // namespace boost

Description

Template Parameters

Key

Key must be Erasable from the container.

Hash

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.

Pred

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.

Allocator

An allocator whose value type is the same as the container’s value type. Allocators using fancy pointers are supported.

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.

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.

If 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.


Configuration Macros

BOOST_UNORDERED_ENABLE_STATS

Globally define this macro to enable statistics calculation for the container. Note that this option decreases the overall performance of many operations.


Typedefs

typedef implementation-defined iterator;

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.

Convertible to const_iterator.


typedef implementation-defined const_iterator;

A constant iterator whose value type is value_type.

The iterator category is at least a forward iterator.


typedef implementation-defined node_type;

A class for holding extracted container elements, modelling NodeHandle.


typedef implementation-defined insert_return_type;

A specialization of an internal class template:

template<class Iterator, class NodeType>
struct insert_return_type // name is exposition only
{
  Iterator position;
  bool     inserted;
  NodeType node;
};

with Iterator = iterator and NodeType = node_type.


Constructors

Default Constructor

unordered_node_set();

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

Postconditions:

size() == 0

Requires:

If the defaults are used, hasher, key_equal and allocator_type need to be DefaultConstructible.


Bucket Count Constructor

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

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.

Postconditions:

size() == 0

Requires:

If the defaults are used, hasher, key_equal and allocator_type need to be DefaultConstructible.


Iterator Range Constructor

template<class InputIterator>
  unordered_node_set(InputIterator f, InputIterator l,
                     size_type n = implementation-defined,
                     const hasher& hf = hasher(),
                     const key_equal& eql = key_equal(),
                     const allocator_type& a = allocator_type());

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.

Requires:

If the defaults are used, hasher, key_equal and allocator_type need to be DefaultConstructible.


Copy Constructor

unordered_node_set(unordered_node_set const& other);

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

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

Requires:

value_type is copy constructible


Move Constructor

unordered_node_set(unordered_node_set&& other);

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 enabled, transfers the internal statistical information from other and calls other.reset_stats().


Iterator Range Constructor with Allocator

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

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.

Requires:

hasher, key_equal need to be DefaultConstructible.


Allocator Constructor

explicit unordered_node_set(Allocator const& a);

Constructs an empty container, using allocator a.


Copy Constructor with Allocator

unordered_node_set(unordered_node_set const& other, Allocator const& a);

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


Move Constructor with Allocator

unordered_node_set(unordered_node_set&& other, Allocator const& a);

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 enabled, transfers the internal statistical information from other iff a == other.get_allocator(), and always calls other.reset_stats().


Move Constructor from concurrent_node_set

unordered_node_set(concurrent_node_set<Key, Hash, Pred, Allocator>&& other);

Move construction from a 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 enabled, transfers the internal statistical information from other and calls other.reset_stats().

Complexity:

Constant time.

Concurrency:

Blocking on other.


Initializer List Constructor

unordered_node_set(std::initializer_list<value_type> il,
              size_type n = implementation-defined
              const hasher& hf = hasher(),
              const key_equal& eql = key_equal(),
              const allocator_type& a = allocator_type());

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.

Requires:

If the defaults are used, hasher, key_equal and allocator_type need to be DefaultConstructible.


Bucket Count Constructor with Allocator

unordered_node_set(size_type n, allocator_type const& a);

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.

Postconditions:

size() == 0

Requires:

hasher and key_equal need to be DefaultConstructible.


Bucket Count Constructor with Hasher and Allocator

unordered_node_set(size_type n, hasher const& hf, allocator_type const& a);

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.

Postconditions:

size() == 0

Requires:

key_equal needs to be DefaultConstructible.


Iterator Range Constructor with Bucket Count and Allocator

template<class InputIterator>
  unordered_node_set(InputIterator f, InputIterator l, size_type n, const allocator_type& a);

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.

Requires:

hasher, key_equal need to be DefaultConstructible.


Iterator Range Constructor with Bucket Count and Hasher

    template<class InputIterator>
      unordered_node_set(InputIterator f, InputIterator l, size_type n, const hasher& hf,
                         const allocator_type& a);

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.

Requires:

key_equal needs to be DefaultConstructible.


initializer_list Constructor with Allocator

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

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

Requires:

hasher and key_equal need to be DefaultConstructible.


initializer_list Constructor with Bucket Count and Allocator

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

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.

Requires:

hasher and key_equal need to be DefaultConstructible.


initializer_list Constructor with Bucket Count and Hasher and Allocator

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

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.

Requires:

key_equal needs to be DefaultConstructible.


Destructor

~unordered_node_set();
Note:

The destructor is applied to every element, and all memory is deallocated


Assignment

Copy Assignment

unordered_node_set& operator=(unordered_node_set const& other);

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.

Requires:

value_type is CopyInsertable


Move Assignment

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 enabled, transfers the internal statistical information from other iff the final allocator is equal to other.get_allocator(), and always calls other.reset_stats().


Initializer List Assignment

unordered_node_set& operator=(std::initializer_list<value_type> il);

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

Requires:

value_type is CopyInsertable

Iterators

begin

iterator begin() noexcept;
const_iterator begin() const noexcept;
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())


end

iterator end() noexcept;
const_iterator end() const noexcept;
Returns:

An iterator which refers to the past-the-end value for the container.


cbegin

const_iterator cbegin() const noexcept;
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())


cend

const_iterator cend() const noexcept;
Returns:

A const_iterator which refers to the past-the-end value for the container.


Size and Capacity

empty

[[nodiscard]] bool empty() const noexcept;
Returns:

size() == 0


size

size_type size() const noexcept;
Returns:

std::distance(begin(), end())


max_size

size_type max_size() const noexcept;
Returns:

size() of the largest possible container.


Modifiers

emplace

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

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.

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.


emplace_hint

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

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.

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

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.


Copy Insert

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

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

Requires:

value_type is 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.


Move Insert

std::pair<iterator, bool> insert(value_type&& obj);

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

Requires:

value_type is 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.


Transparent Insert

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

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.

Requires:

value_type is 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.


Copy Insert with Hint

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.

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

Requires:

value_type is 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.


Move Insert with Hint

iterator insert(const_iterator hint, value_type&& obj);

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

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

Requires:

value_type is 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.


Transparent Insert with Hint

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

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.

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

Requires:

value_type is 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.


Insert Iterator Range

template<class InputIterator> void insert(InputIterator first, InputIterator last);

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.

Requires:

value_type is 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.


Insert Initializer List

void insert(std::initializer_list<value_type>);

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.

Requires:

value_type is 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.


Insert Node

insert_return_type insert(node_type&& nh);

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.

Returns:

An insert_return_type object constructed from position, inserted and node:

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

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

  • 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().

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.


Insert Node with Hint

iterator insert(const_iterator hint, node_type&& nh);

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.

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

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.


Erase by Position

convertible-to-iterator erase(iterator position);
convertible-to-iterator erase(const_iterator position);

Erase the element pointed to by position.

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.


Erase by Key

size_type erase(const key_type& k);
template<class K> size_type erase(K&& k);

Erase all elements with key equivalent to k.

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.


Erase Range

iterator erase(const_iterator first, const_iterator last);

Erases the elements in the range from first to last.

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).


swap

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

Swaps the contents of the container with the parameter.

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.

Throws:

Nothing unless key_equal or hasher throw on swapping.


Extract by Position

node_type extract(const_iterator position);

Extracts the element pointed to by position.

Returns:

A node_type object holding the extracted element.

Throws:

Nothing.


Extract by Key

node_type extract(const key_type& k);
template<class K> node_type extract(K&& k);

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

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.


clear

void clear() noexcept;

Erases all elements in the container.

Postconditions:

size() == 0, max_load() >= max_load_factor() * bucket_count()


merge

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);

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

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.


Observers

get_allocator

allocator_type get_allocator() const noexcept;
Returns:

The container’s allocator.


hash_function

hasher hash_function() const;
Returns:

The container’s hash function.


key_eq

key_equal key_eq() const;
Returns:

The container’s key equality predicate


Lookup

find

iterator         find(const key_type& k);
const_iterator   find(const key_type& k) const;
template<class K>
  iterator       find(const K& k);
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.


count

size_type        count(const key_type& k) const;
template<class K>
  size_type      count(const K& k) const;
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.


contains

bool             contains(const key_type& k) const;
template<class K>
  bool           contains(const K& k) const;
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.


equal_range

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;
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.


Bucket Interface

bucket_count

size_type bucket_count() const noexcept;
Returns:

The size of the bucket array.


Hash Policy

load_factor

float load_factor() const noexcept;
Returns:

static_cast<float>(size())/static_cast<float>(bucket_count()), or 0 if bucket_count() == 0.


max_load_factor

float max_load_factor() const noexcept;
Returns:

Returns the container’s maximum load factor.


Set max_load_factor

void max_load_factor(float z);
Effects:

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


max_load

size_type max_load() const noexcept;
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.


rehash

void rehash(size_type n);

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.

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

Invalidates iterators and changes the order of elements.

Throws:

The function has no effect if an exception is thrown, unless it is thrown by the container’s hash function or comparison function.


reserve

void reserve(size_type n);

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

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

Invalidates iterators and changes the order of elements.

Throws:

The function has no effect if an exception is thrown, unless it is thrown by the container’s hash function or comparison function.


Statistics

get_stats

stats get_stats() const;
Returns:

A statistical description of the insertion and lookup operations performed by the container so far.

Notes:

Only available if statistics calculation is enabled.


reset_stats

void reset_stats() noexcept;
Effects:

Sets to zero the internal statistics kept by the container.

Notes:

Only available if statistics calculation is enabled.


Deduction Guides

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

  • 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.

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.

iter-value-type

template<class InputIterator>
  using iter-value-type =
    typename std::iterator_traits<InputIterator>::value_type; // exposition only

Equality Comparisons

operator==

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);

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).

Notes:

Behavior is undefined if the two containers don’t have equivalent equality predicates.


operator!=

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);

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).

Notes:

Behavior is undefined if the two containers don’t have equivalent equality predicates.

Swap

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)));

Swaps the contents of x and y.

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.

Effects:

x.swap(y)

Throws:

Nothing unless key_equal or hasher throw on swapping.


erase_if

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);

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

Returns:

The number of erased elements.

Notes:

Equivalent to:

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();

Serialization

unordered_node_sets can be archived/retrieved by means of Boost.Serialization using the API provided by this library. Both regular and XML archives are supported.

Saving an unordered_node_set to an archive

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

Requires:

value_type is serializable (XML serializable), and it supports Boost.Serialization save_construct_data/load_construct_data protocol (automatically suported by DefaultConstructible types).


Loading an unordered_node_set from an archive

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.

Requires:

value_type is MoveInsertable. x.key_equal() is functionally equivalent to other.key_equal().


Saving an iterator/const_iterator to an archive

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

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.


Loading an iterator/const_iterator from an archive

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.

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.