An unordered associative container that stores unique values. For the normative reference see chapter 23 of the working draft of the C++ standard [n2461]. Template Parameters Value Value must be Assignable and CopyConstructible Hash A unary function object type that acts a hash function for a Value. It takes a single argument of type Value and returns a value of type std::size_t. Pred A binary function object that implements an equivalence relation on values of type Value. 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. Alloc An allocator whose value type is the same as the container's value type. The elements are organized into buckets. Keys with the same hash code are stored in the same bucket. The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash. Value Value Hash Pred Alloc typename allocator_type::pointer typename allocator_type::const_pointer typename allocator_type::reference lvalue of value_type. typename allocator_type::const_reference const lvalue of value_type. implementation-defined An unsigned integral type. size_type can represent any non-negative value of difference_type. implementation-defined A signed integral type. Is identical to the difference type of iterator and const_iterator. implementation-defined A constant iterator whose value type is value_type. Any iterator category except output iterator. Convertible to const_iterator. implementation-defined A constant iterator whose value type is value_type. Any iterator category except output iterator. implementation-defined An iterator with the same value type, difference type and pointer and reference type as iterator. A local_iterator object can be used to iterate through a single bucket. implementation-defined A constant iterator with the same value type, difference type and pointer and reference type as const_iterator. A const_local_iterator object can be used to iterate through a single bucket. size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() size() == 0 Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocatorand a maximum load factor of 1.0. InputIterator InputIterator size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocator and a maximum load factor of 1.0 and inserts the elements from [f, l) into it. unordered_set const& The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator. unordered_set const& unordered_set& The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator. allocator_type bool size() == 0 size_type std::distance(begin(), end()) size_type size() of the largest possible container. iterator const_iterator An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. iterator const_iterator An iterator which refers to the past-the-end value for the container. const_iterator A constant iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. const_iterator A constant iterator which refers to the past-the-end value for the container. value_type const& std::pair<iterator, bool> Inserts obj in the container if and only if there is no element in the container with an equivalent value. 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 elment with equivalent value. If an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator value_type const& iterator Inserts obj in the container if and only if there is no element in the container with an equivalent value. hint is a suggestion to where the element should be inserted. If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the elment with equivalent value. If an exception is thrown by an operation other than a call to hasher the function has no effect. The standard is fairly vague on the meaning of the hint. But the only practical way to use it, and the only way that Boost.Unordered supports is to point to an existing element with the same value. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. InputIterator InputIterator void 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 value. When inserting a single element, if an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator iterator Erase the element pointed to by position. The iterator following position before the erasure. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. key_type const& size_type Erase all elements with key equivalent to k. The number of elements erased. Only throws an exception, if it is thrown by a call to hasher or key_equal. const_iterator const_iterator iterator Erases the elements in the range from first to last. The iterator following the erased elements - i.e. last. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. void Erases all elements in the container. size() == 0 Never throws an exception. unordered_set& void Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of key_equal or hasher. hasher The container's hash function. key_equal The container's key equality predicate. key_type const& iterator key_type const& iterator An iterator pointing to an element with key equivalent to k, or b.end() if no such element exists. key_type const& size_type The number of elements with key equivalent to k. key_type const& std::pair<iterator, iterator> key_type const& std::pair<iterator, iterator> A range containing all elements with key equivalent to k. If the container doesn't container any such elements, returns std::make_pair(b.end(),b.end()). size_type The number of buckets. size_type An upper bound on the number of buckets. size_type size_type n < bucket_count() The number of elements in bucket n. key_type const& size_type The index of the bucket which would contain an element with key k. The return value is less than bucket_count() size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the first element in the bucket with index n. size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the 'one past the end' element in the bucket with index n. float The average number of elements per bucket. float Returns the current maximum load factor. float float Changes the container's maximum load factor, using z as a hint. size_type void Changes the number of buckets so that there at least n buckets, and so that the load factor is less than the maximum load factor. Invalidates iterators, and changes the order of elements The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function. unordered_set<Key, T, Hash, Pred, Alloc>& unordered_set<Key, T, Hash, Pred, Alloc>& void x.swap(y) Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of Hash or Pred. An unordered associative container that stores values. The same key can be stored multiple times. For the normative reference see chapter 23 of the working draft of the C++ standard [n2461]. Template Parameters Value Value must be Assignable and CopyConstructible Hash A unary function object type that acts a hash function for a Value. It takes a single argument of type Value and returns a value of type std::size_t. Pred A binary function object that implements an equivalence relation on values of type Value. 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. Alloc An allocator whose value type is the same as the container's value type. The elements are organized into buckets. Keys with the same hash code are stored in the same bucket and elements with equivalent keys are stored next to each other. The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash. Value Value Hash Pred Alloc typename allocator_type::pointer typename allocator_type::const_pointer typename allocator_type::reference lvalue of value_type. typename allocator_type::const_reference const lvalue of value_type. implementation-defined An unsigned integral type. size_type can represent any non-negative value of difference_type. implementation-defined A signed integral type. Is identical to the difference type of iterator and const_iterator. implementation-defined A constant iterator whose value type is value_type. Any iterator category except output iterator. Convertible to const_iterator. implementation-defined A constant iterator whose value type is value_type. Any iterator category except output iterator. implementation-defined An iterator with the same value type, difference type and pointer and reference type as iterator. A local_iterator object can be used to iterate through a single bucket. implementation-defined A constant iterator with the same value type, difference type and pointer and reference type as const_iterator. A const_local_iterator object can be used to iterate through a single bucket. size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() size() == 0 Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocatorand a maximum load factor of 1.0. InputIterator InputIterator size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocator and a maximum load factor of 1.0 and inserts the elements from [f, l) into it. unordered_multiset const& The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator. unordered_multiset const& unordered_multiset& The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator. allocator_type bool size() == 0 size_type std::distance(begin(), end()) size_type size() of the largest possible container. iterator const_iterator An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. iterator const_iterator An iterator which refers to the past-the-end value for the container. const_iterator A constant iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. const_iterator A constant iterator which refers to the past-the-end value for the container. value_type const& iterator Inserts obj in the container. An iterator pointing to the inserted element. If an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator value_type const& iterator Inserts obj in the container. hint is a suggestion to where the element should be inserted. An iterator pointing to the inserted element. If an exception is thrown by an operation other than a call to hasher the function has no effect. The standard is fairly vague on the meaning of the hint. But the only practical way to use it, and the only way that Boost.Unordered supports is to point to an existing element with the same value. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. InputIterator InputIterator void Inserts a range of elements into the container. When inserting a single element, if an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator iterator Erase the element pointed to by position. The iterator following position before the erasure. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. key_type const& size_type Erase all elements with key equivalent to k. The number of elements erased. Only throws an exception, if it is thrown by a call to hasher or key_equal. const_iterator const_iterator iterator Erases the elements in the range from first to last. The iterator following the erased elements - i.e. last. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. void Erases all elements in the container. size() == 0 Never throws an exception. unordered_multiset& void Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of key_equal or hasher. hasher The container's hash function. key_equal The container's key equality predicate. key_type const& iterator key_type const& iterator An iterator pointing to an element with key equivalent to k, or b.end() if no such element exists. key_type const& size_type The number of elements with key equivalent to k. key_type const& std::pair<iterator, iterator> key_type const& std::pair<iterator, iterator> A range containing all elements with key equivalent to k. If the container doesn't container any such elements, returns std::make_pair(b.end(),b.end()). size_type The number of buckets. size_type An upper bound on the number of buckets. size_type size_type n < bucket_count() The number of elements in bucket n. key_type const& size_type The index of the bucket which would contain an element with key k. The return value is less than bucket_count() size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the first element in the bucket with index n. size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the 'one past the end' element in the bucket with index n. float The average number of elements per bucket. float Returns the current maximum load factor. float float Changes the container's maximum load factor, using z as a hint. size_type void Changes the number of buckets so that there at least n buckets, and so that the load factor is less than the maximum load factor. Invalidates iterators, and changes the order of elements The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function. unordered_multiset<Key, T, Hash, Pred, Alloc>& unordered_multiset<Key, T, Hash, Pred, Alloc>& void x.swap(y) Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of Hash or Pred.

An unordered associative container that associates unique keys with another value. For the normative reference see chapter 23 of the working draft of the C++ standard [n2461]. Template Parameters Key Key must be Assignable and CopyConstructible. T T must be CopyConstructible 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 implements an equivalence relation on values of type Key. 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. Alloc An allocator whose value type is the same as the container's value type. The elements are organized into buckets. Keys with the same hash code are stored in the same bucket. The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash. Key std::pair<Key const, Value> T Hash Pred Alloc typename allocator_type::pointer typename allocator_type::const_pointer typename allocator_type::reference lvalue of value_type. typename allocator_type::const_reference const lvalue of value_type. implementation-defined An unsigned integral type. size_type can represent any non-negative value of difference_type. implementation-defined A signed integral type. Is identical to the difference type of iterator and const_iterator. implementation-defined A iterator whose value type is value_type. Any iterator category except output iterator. Convertible to const_iterator. implementation-defined A constant iterator whose value type is value_type. Any iterator category except output iterator. implementation-defined An iterator with the same value type, difference type and pointer and reference type as iterator. A local_iterator object can be used to iterate through a single bucket. implementation-defined A constant iterator with the same value type, difference type and pointer and reference type as const_iterator. A const_local_iterator object can be used to iterate through a single bucket. size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() size() == 0 Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocatorand a maximum load factor of 1.0. InputIterator InputIterator size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocator and a maximum load factor of 1.0 and inserts the elements from [f, l) into it. unordered_map const& The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator. unordered_map const& unordered_map& The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator. allocator_type bool size() == 0 size_type std::distance(begin(), end()) size_type size() of the largest possible container. iterator const_iterator An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. iterator const_iterator An iterator which refers to the past-the-end value for the container. const_iterator A constant iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. const_iterator A constant iterator which refers to the past-the-end value for the container. value_type const& std::pair<iterator, bool> Inserts obj in the container if and only if there is no element in the container with an equivalent key. 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 elment with equivalent key. If an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator value_type const& iterator 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. If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the elment with equivalent key. If an exception is thrown by an operation other than a call to hasher the function has no effect. The standard is fairly vague on the meaning of the hint. But the only practical way to use it, and the only way that Boost.Unordered supports is to point to an existing element with the same key. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. InputIterator InputIterator void 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. When inserting a single element, if an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator iterator Erase the element pointed to by position. The iterator following position before the erasure. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. key_type const& size_type Erase all elements with key equivalent to k. The number of elements erased. Only throws an exception, if it is thrown by a call to hasher or key_equal. const_iterator const_iterator iterator Erases the elements in the range from first to last. The iterator following the erased elements - i.e. last. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. void Erases all elements in the container. size() == 0 Never throws an exception. unordered_map& void Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of key_equal or hasher. hasher The container's hash function. key_equal The container's key equality predicate. key_type const& iterator key_type const& iterator An iterator pointing to an element with key equivalent to k, or b.end() if no such element exists. key_type const& size_type The number of elements with key equivalent to k. key_type const& std::pair<iterator, iterator> key_type const& std::pair<iterator, iterator> A range containing all elements with key equivalent to k. If the container doesn't container any such elements, returns std::make_pair(b.end(),b.end()). key_type const& mapped_type& If the container does not already contain an elements with a key equivalent to k, inserts the value std::pair<key_type const, mapped_type>(k, mapped_type()) A reference to x.second where x is the element already in the container, or the newly inserted element with a key equivalent to k If an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. T& key_type const& T const& key_type const& A reference to x.second where x is the (unique) element whose key is equivalent to k. An exception object of type out_of_range if no such element is present. This is not specified in the draft standard, but that is probably an oversight. The issue has been raised in comp.std.c++. size_type The number of buckets. size_type An upper bound on the number of buckets. size_type size_type n < bucket_count() The number of elements in bucket n. key_type const& size_type The index of the bucket which would contain an element with key k. The return value is less than bucket_count() size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the first element in the bucket with index n. size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the 'one past the end' element in the bucket with index n. float The average number of elements per bucket. float Returns the current maximum load factor. float float Changes the container's maximum load factor, using z as a hint. size_type void Changes the number of buckets so that there at least n buckets, and so that the load factor is less than the maximum load factor. Invalidates iterators, and changes the order of elements The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function. unordered_map<Key, T, Hash, Pred, Alloc>& unordered_map<Key, T, Hash, Pred, Alloc>& void x.swap(y) Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of Hash or Pred. An unordered associative container that associates keys with another value. The same key can be stored multiple times. For the normative reference see chapter 23 of the working draft of the C++ standard [n2461]. Template Parameters Key Key must be Assignable and CopyConstructible. T T must be CopyConstructible 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 implements an equivalence relation on values of type Key. 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. Alloc An allocator whose value type is the same as the container's value type. The elements are organized into buckets. Keys with the same hash code are stored in the same bucket and elements with equivalent keys are stored next to each other. The number of buckets can be automatically increased by a call to insert, or as the result of calling rehash. Key std::pair<Key const, Value> T Hash Pred Alloc typename allocator_type::pointer typename allocator_type::const_pointer typename allocator_type::reference lvalue of value_type. typename allocator_type::const_reference const lvalue of value_type. implementation-defined An unsigned integral type. size_type can represent any non-negative value of difference_type. implementation-defined A signed integral type. Is identical to the difference type of iterator and const_iterator. implementation-defined A iterator whose value type is value_type. Any iterator category except output iterator. Convertible to const_iterator. implementation-defined A constant iterator whose value type is value_type. Any iterator category except output iterator. implementation-defined An iterator with the same value type, difference type and pointer and reference type as iterator. A local_iterator object can be used to iterate through a single bucket. implementation-defined A constant iterator with the same value type, difference type and pointer and reference type as const_iterator. A const_local_iterator object can be used to iterate through a single bucket. size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() size() == 0 Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocatorand a maximum load factor of 1.0. InputIterator InputIterator size_type implementation-defined hasher const& hasher() key_equal const& key_equal() allocator_type const& allocator_type() Constructs an empty container with at least n buckets, using hf as the hash function, eq as the key equality predicate, a as the allocator and a maximum load factor of 1.0 and inserts the elements from [f, l) into it. unordered_multimap const& The copy constructor. Copies the contained elements, hash function, predicate, maximum load factor and allocator. unordered_multimap const& unordered_multimap& The assignment operator. Copies the contained elements, hash function, predicate and maximum load factor but not the allocator. allocator_type bool size() == 0 size_type std::distance(begin(), end()) size_type size() of the largest possible container. iterator const_iterator An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. iterator const_iterator An iterator which refers to the past-the-end value for the container. const_iterator A constant iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container. const_iterator A constant iterator which refers to the past-the-end value for the container. value_type const& iterator Inserts obj in the container. An iterator pointing to the inserted element. If an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator value_type const& iterator Inserts obj in the container. hint is a suggestion to where the element should be inserted. An iterator pointing to the inserted element. If an exception is thrown by an operation other than a call to hasher the function has no effect. The standard is fairly vague on the meaning of the hint. But the only practical way to use it, and the only way that Boost.Unordered supports is to point to an existing element with the same key. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. InputIterator InputIterator void Inserts a range of elements into the container. When inserting a single element, if an exception is thrown by an operation other than a call to hasher the function has no effect. Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. const_iterator iterator Erase the element pointed to by position. The iterator following position before the erasure. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. key_type const& size_type Erase all elements with key equivalent to k. The number of elements erased. Only throws an exception, if it is thrown by a call to hasher or key_equal. const_iterator const_iterator iterator Erases the elements in the range from first to last. The iterator following the erased elements - i.e. last. Only throws an exception, if it is thrown by a call to hasher or key_equal. They don't get called by the current implementation Boost.Unordered but other implementations may call them. void Erases all elements in the container. size() == 0 Never throws an exception. unordered_multimap& void Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of key_equal or hasher. hasher The container's hash function. key_equal The container's key equality predicate. key_type const& iterator key_type const& iterator An iterator pointing to an element with key equivalent to k, or b.end() if no such element exists. key_type const& size_type The number of elements with key equivalent to k. key_type const& std::pair<iterator, iterator> key_type const& std::pair<iterator, iterator> A range containing all elements with key equivalent to k. If the container doesn't container any such elements, returns std::make_pair(b.end(),b.end()). size_type The number of buckets. size_type An upper bound on the number of buckets. size_type size_type n < bucket_count() The number of elements in bucket n. key_type const& size_type The index of the bucket which would contain an element with key k. The return value is less than bucket_count() size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the first element in the bucket with index n. size_type local_iterator size_type const_local_iterator n shall be in the range [0, bucket_count()). A local iterator pointing the 'one past the end' element in the bucket with index n. float The average number of elements per bucket. float Returns the current maximum load factor. float float Changes the container's maximum load factor, using z as a hint. size_type void Changes the number of buckets so that there at least n buckets, and so that the load factor is less than the maximum load factor. Invalidates iterators, and changes the order of elements The function has no effect if an exception is thrown, unless it is thrown by the container's hash function or comparison function. unordered_multimap<Key, T, Hash, Pred, Alloc>& unordered_multimap<Key, T, Hash, Pred, Alloc>& void x.swap(y) Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of Hash or Pred.