libstdc++
std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits > Class Template Reference
Inheritance diagram for std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits >:
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Public Types

typedef _Alloc allocator_type
 
using const_iterator = typename __insert_base::const_iterator
 
using const_local_iterator = __detail::_Local_const_iterator< key_type, _Value, _ExtractKey, _Hash, _RangeHash, _Unused, __constant_iterators::value, __hash_cached::value >
 
typedef __value_alloc_traits::const_pointer const_pointer
 
typedef const value_type & const_reference
 
using difference_type = typename __hashtable_base::difference_type
 
typedef _Hash hasher
 
using insert_return_type = _Node_insert_return< iterator, node_type >
 
using iterator = typename __insert_base::iterator
 
typedef _Equal key_equal
 
typedef _Key key_type
 
using local_iterator = __detail::_Local_iterator< key_type, _Value, _ExtractKey, _Hash, _RangeHash, _Unused, __constant_iterators::value, __hash_cached::value >
 
using node_type = _Node_handle< _Key, _Value, __node_alloc_type >
 
typedef __value_alloc_traits::pointer pointer
 
typedef value_type & reference
 
using size_type = typename __hashtable_base::size_type
 
typedef _Value value_type
 

Public Member Functions

 _Hashtable (_Hashtable &&__ht) noexcept(_S_nothrow_move())
 
 _Hashtable (_Hashtable &&__ht, const allocator_type &__a) noexcept(_S_nothrow_move< __node_alloc_traits::_S_always_equal()>())
 
template<typename _InputIterator >
 _Hashtable (_InputIterator __f, _InputIterator __l, size_type __bkt_count_hint=0, const _Hash &__hf=_Hash(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
 
 _Hashtable (const _Hashtable &)
 
 _Hashtable (const _Hashtable &, const allocator_type &)
 
 _Hashtable (const allocator_type &__a)
 
 _Hashtable (initializer_list< value_type > __l, size_type __bkt_count_hint=0, const _Hash &__hf=_Hash(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
 
 _Hashtable (size_type __bkt_count_hint, const _Hash &__hf=_Hash(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
 
const _RehashPolicy & __rehash_policy () const
 
void __rehash_policy (const _RehashPolicy &__pol)
 
template<typename... _Args>
auto _M_emplace (const_iterator __hint, false_type, _Args &&... __args) -> iterator
 
template<typename... _Args>
auto _M_emplace (true_type, _Args &&... __args) -> pair< iterator, bool >
 
template<typename _Kt >
auto _M_find_before_node_tr (size_type __bkt, const _Kt &__k, __hash_code __code) const -> __node_base_ptr
 
template<typename _Arg , typename _NodeGenerator >
auto _M_insert (const_iterator __hint, _Arg &&__v, const _NodeGenerator &__node_gen, false_type) -> iterator
 
template<typename _Kt , typename _Arg , typename _NodeGenerator >
auto _M_insert_unique (_Kt &&__k, _Arg &&__v, const _NodeGenerator &__node_gen) -> pair< iterator, bool >
 
template<typename _Compatible_Hashtable >
void _M_merge_multi (_Compatible_Hashtable &__src) noexcept
 
template<typename _Compatible_Hashtable >
void _M_merge_unique (_Compatible_Hashtable &__src) noexcept
 
insert_return_type _M_reinsert_node (node_type &&__nh)
 
iterator _M_reinsert_node_multi (const_iterator __hint, node_type &&__nh)
 
const_iterator begin () const noexcept
 
iterator begin () noexcept
 
local_iterator begin (size_type __bkt)
 
const_local_iterator begin (size_type __bkt) const
 
size_type bucket (const key_type &__k) const
 
size_type bucket_count () const noexcept
 
size_type bucket_size (size_type __bkt) const
 
const_iterator cbegin () const noexcept
 
const_local_iterator cbegin (size_type __bkt) const
 
const_iterator cend () const noexcept
 
const_local_iterator cend (size_type __bkt) const
 
void clear () noexcept
 
size_type count (const key_type &__k) const
 
template<typename... _Args>
__ireturn_type emplace (_Args &&... __args)
 
template<typename... _Args>
iterator emplace_hint (const_iterator __hint, _Args &&... __args)
 
bool empty () const noexcept
 
const_iterator end () const noexcept
 
iterator end () noexcept
 
local_iterator end (size_type __bkt)
 
const_local_iterator end (size_type __bkt) const
 
std::pair< iterator, iterator > equal_range (const key_type &__k)
 
std::pair< const_iterator, const_iterator > equal_range (const key_type &__k) const
 
size_type erase (const key_type &__k)
 
iterator erase (const_iterator)
 
iterator erase (const_iterator, const_iterator)
 
iterator erase (iterator __it)
 
node_type extract (const _Key &__k)
 
node_type extract (const_iterator __pos)
 
iterator find (const key_type &__k)
 
const_iterator find (const key_type &__k) const
 
allocator_type get_allocator () const noexcept
 
hasher hash_function () const
 
key_equal key_eq () const
 
float load_factor () const noexcept
 
size_type max_bucket_count () const noexcept
 
size_type max_size () const noexcept
 
_Hashtableoperator= (_Hashtable &&__ht) noexcept(__node_alloc_traits::_S_nothrow_move() &&is_nothrow_move_assignable< _Hash >::value &&is_nothrow_move_assignable< _Equal >::value)
 
_Hashtableoperator= (const _Hashtable &__ht)
 
_Hashtableoperator= (initializer_list< value_type > __l)
 
void rehash (size_type __bkt_count)
 
size_type size () const noexcept
 
void swap (_Hashtable &) noexcept(__and_< __is_nothrow_swappable< _Hash >, __is_nothrow_swappable< _Equal >>::value)
 

Protected Member Functions

std::size_t _M_bucket_index (__hash_code __c, std::size_t __bkt_count) const
 
std::size_t _M_bucket_index (const _Hash_node_value< _Value, false > &__n, std::size_t __bkt_count) const noexcept(noexcept(declval< const _Hash & >()(declval< const _Key & >())) &&noexcept(declval< const _RangeHash & >()((__hash_code) 0,(std::size_t) 0)))
 
std::size_t _M_bucket_index (const _Hash_node_value< _Value, true > &__n, std::size_t __bkt_count) const noexcept(noexcept(declval< const _RangeHash & >()((__hash_code) 0,(std::size_t) 0)))
 
void _M_copy_code (_Hash_node_code_cache< false > &, const _Hash_node_code_cache< false > &) const
 
void _M_copy_code (_Hash_node_code_cache< true > &__to, const _Hash_node_code_cache< true > &__from) const
 
const _Equal & _M_eq () const
 
bool _M_equals (const _Key &__k, __hash_code __c, const _Hash_node_value< _Value, __hash_cached::value > &__n) const
 
template<typename _Kt >
bool _M_equals_tr (const _Kt &__k, __hash_code __c, const _Hash_node_value< _Value, __hash_cached::value > &__n) const
 
const _Hash & _M_hash () const
 
__hash_code _M_hash_code (const _Key &__k) const
 
__hash_code _M_hash_code_tr (const _Kt &__k) const
 
bool _M_node_equals (const _Hash_node_value< _Value, __hash_cached::value > &__lhn, const _Hash_node_value< _Value, __hash_cached::value > &__rhn) const
 
void _M_store_code (_Hash_node_code_cache< false > &, __hash_code) const
 
void _M_store_code (_Hash_node_code_cache< true > &__n, __hash_code __c) const
 
void _M_swap (_Hash_code_base &__x)
 
void _M_swap (_Hashtable_base &__x)
 

Friends

template<typename _Keya , typename _Valuea , typename _Alloca , typename _ExtractKeya , typename _Equala , typename _Hasha , typename _RangeHasha , typename _Unuseda , typename _RehashPolicya , typename _Traitsa , bool _Unique_keysa>
struct __detail::_Equality
 
template<typename _Keya , typename _Valuea , typename _Alloca , typename _ExtractKeya , typename _Equala , typename _Hasha , typename _RangeHasha , typename _Unuseda , typename _RehashPolicya , typename _Traitsa , bool _Constant_iteratorsa>
struct __detail::_Insert
 
template<typename _Keya , typename _Valuea , typename _Alloca , typename _ExtractKeya , typename _Equala , typename _Hasha , typename _RangeHasha , typename _Unuseda , typename _RehashPolicya , typename _Traitsa >
struct __detail::_Insert_base
 
template<typename _Keya , typename _Valuea , typename _Alloca , typename _ExtractKeya , typename _Equala , typename _Hasha , typename _RangeHasha , typename _Unuseda , typename _RehashPolicya , typename _Traitsa , bool _Unique_keysa>
struct __detail::_Map_base
 

Detailed Description

template<typename _Key, typename _Value, typename _Alloc, typename _ExtractKey, typename _Equal, typename _Hash, typename _RangeHash, typename _Unused, typename _RehashPolicy, typename _Traits>
class std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits >

Primary class template _Hashtable.

Template Parameters
_ValueCopyConstructible type.
_KeyCopyConstructible type.
_AllocAn allocator type ([lib.allocator.requirements]) whose _Alloc::value_type is _Value. As a conforming extension, we allow for _Alloc::value_type != _Value.
_ExtractKeyFunction object that takes an object of type _Value and returns a value of type _Key.
_EqualFunction object that takes two objects of type k and returns a bool-like value that is true if the two objects are considered equal.
_HashThe hash function. A unary function object with argument type _Key and result type size_t. Return values should be distributed over the entire range [0, numeric_limits<size_t>:::max()].
_RangeHashThe range-hashing function (in the terminology of Tavori and Dreizin). A binary function object whose argument types and result type are all size_t. Given arguments r and N, the return value is in the range [0, N).
_UnusedNot used.
_RehashPolicyPolicy class with three members, all of which govern the bucket count. _M_next_bkt(n) returns a bucket count no smaller than n. _M_bkt_for_elements(n) returns a bucket count appropriate for an element count of n. _M_need_rehash(n_bkt, n_elt, n_ins) determines whether, if the current bucket count is n_bkt and the current element count is n_elt, we need to increase the bucket count for n_ins insertions. If so, returns make_pair(true, n), where n is the new bucket count. If not, returns make_pair(false, <anything>)
_TraitsCompile-time class with three boolean std::integral_constant members: __cache_hash_code, __constant_iterators, __unique_keys.

Each _Hashtable data structure has:

  • _Bucket[] _M_buckets
  • _Hash_node_base _M_before_begin
  • size_type _M_bucket_count
  • size_type _M_element_count

with _Bucket being _Hash_node_base* and _Hash_node containing:

  • _Hash_node* _M_next
  • Tp _M_value
  • size_t _M_hash_code if cache_hash_code is true

In terms of Standard containers the hashtable is like the aggregation of:

  • std::forward_list<_Node> containing the elements
  • std::vector<std::forward_list<_Node>::iterator> representing the buckets

The non-empty buckets contain the node before the first node in the bucket. This design makes it possible to implement something like a std::forward_list::insert_after on container insertion and std::forward_list::erase_after on container erase calls. _M_before_begin is equivalent to std::forward_list::before_begin. Empty buckets contain nullptr. Note that one of the non-empty buckets contains &_M_before_begin which is not a dereferenceable node so the node pointer in a bucket shall never be dereferenced, only its next node can be.

Walking through a bucket's nodes requires a check on the hash code to see if each node is still in the bucket. Such a design assumes a quite efficient hash functor and is one of the reasons it is highly advisable to set __cache_hash_code to true.

The container iterators are simply built from nodes. This way incrementing the iterator is perfectly efficient independent of how many empty buckets there are in the container.

On insert we compute the element's hash code and use it to find the bucket index. If the element must be inserted in an empty bucket we add it at the beginning of the singly linked list and make the bucket point to _M_before_begin. The bucket that used to point to _M_before_begin, if any, is updated to point to its new before begin node.

On erase, the simple iterator design requires using the hash functor to get the index of the bucket to update. For this reason, when __cache_hash_code is set to false the hash functor must not throw and this is enforced by a static assertion.

Functionality is implemented by decomposition into base classes, where the derived _Hashtable class is used in _Map_base, _Insert, _Rehash_base, and _Equality base classes to access the "this" pointer. _Hashtable_base is used in the base classes as a non-recursive, fully-completed-type so that detailed nested type information, such as iterator type and node type, can be used. This is similar to the "Curiously Recurring Template Pattern" (CRTP) technique, but uses a reconstructed, not explicitly passed, template pattern.

Base class templates are:

  • __detail::_Hashtable_base
  • __detail::_Map_base
  • __detail::_Insert
  • __detail::_Rehash_base
  • __detail::_Equality

Definition at line 168 of file bits/hashtable.h.

Member Function Documentation

◆ _M_merge_multi()

template<typename _Key , typename _Value , typename _Alloc , typename _ExtractKey , typename _Equal , typename _Hash , typename _RangeHash , typename _Unused , typename _RehashPolicy , typename _Traits >
template<typename _Compatible_Hashtable >
void std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits >::_M_merge_multi ( _Compatible_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits > &  __src)
inlinenoexcept

Merge from a compatible container into one with equivalent keys.

Definition at line 1087 of file bits/hashtable.h.

◆ _M_merge_unique()

template<typename _Key , typename _Value , typename _Alloc , typename _ExtractKey , typename _Equal , typename _Hash , typename _RangeHash , typename _Unused , typename _RehashPolicy , typename _Traits >
template<typename _Compatible_Hashtable >
void std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits >::_M_merge_unique ( _Compatible_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits > &  __src)
inlinenoexcept

Merge from a compatible container into one with unique keys.

Definition at line 1059 of file bits/hashtable.h.

◆ _M_reinsert_node()

template<typename _Key , typename _Value , typename _Alloc , typename _ExtractKey , typename _Equal , typename _Hash , typename _RangeHash , typename _Unused , typename _RehashPolicy , typename _Traits >
insert_return_type std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits >::_M_reinsert_node ( node_type &&  __nh)
inline

Re-insert an extracted node into a container with unique keys.

Definition at line 967 of file bits/hashtable.h.

References std::end().

Referenced by std::unordered_map< _Key, _Tp, _Hash, _Pred, _Alloc >::insert(), and std::unordered_set< _Value, _Hash, _Pred, _Alloc >::insert().

◆ _M_reinsert_node_multi()

template<typename _Key , typename _Value , typename _Alloc , typename _ExtractKey , typename _Equal , typename _Hash , typename _RangeHash , typename _Unused , typename _RehashPolicy , typename _Traits >
iterator std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits >::_M_reinsert_node_multi ( const_iterator  __hint,
node_type &&  __nh 
)
inline

Re-insert an extracted node into a container with equivalent keys.

Definition at line 998 of file bits/hashtable.h.

References std::end().

Referenced by std::unordered_multimap< _Key, _Tp, _Hash, _Pred, _Alloc >::insert(), and std::unordered_multiset< _Value, _Hash, _Pred, _Alloc >::insert().

◆ extract()

template<typename _Key , typename _Value , typename _Alloc , typename _ExtractKey , typename _Equal , typename _Hash , typename _RangeHash , typename _Unused , typename _RehashPolicy , typename _Traits >
node_type std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits >::extract ( const _Key &  __k)
inline

Extract a node.

Definition at line 1046 of file bits/hashtable.h.


The documentation for this class was generated from the following file: