std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits > Class Template Reference
Containers » Unordered Associative » Base and Implementation Classes
Inheritance diagram for std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits >:
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## Public Types

typedef _Alloc | allocator_type
using | const_iterator = typename __hashtable_base::const_iterator
using | const_local_iterator = typename __hashtable_base::const_local_iterator
typedef __value_alloc_traits::const_pointer | const_pointer
typedef const value_type & | const_reference
using | difference_type = typename __hashtable_base::difference_type
using | iterator = typename __hashtable_base::iterator
typedef _Equal | key_equal
typedef _Key | key_type
using | local_iterator = typename __hashtable_base::local_iterator
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 (size_type __bucket_hint, const _H1 &, const _H2 &, const _Hash &, const _Equal &, const _ExtractKey &, const allocator_type &)
template<typename _InputIterator >
| _Hashtable (_InputIterator __first, _InputIterator __last, size_type __bucket_hint, const _H1 &, const _H2 &, const _Hash &, const _Equal &, const _ExtractKey &, const allocator_type &)
| _Hashtable (const _Hashtable &)
| _Hashtable (_Hashtable &&) noexcept
| _Hashtable (const _Hashtable &, const allocator_type &)
| _Hashtable (_Hashtable &&, const allocator_type &)
| _Hashtable (const allocator_type &__a)
| _Hashtable (size_type __n, const _H1 &__hf=_H1(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
template<typename _InputIterator >
| _Hashtable (_InputIterator __f, _InputIterator __l, size_type __n=0, const _H1 &__hf=_H1(), const key_equal &__eql=key_equal(), const allocator_type &__a=allocator_type())
| _Hashtable (initializer_list< value_type > __l, size_type __n=0, const _H1 &__hf=_H1(), 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 (std::true_type, _Args &&... __args) -> pair< iterator, bool >
template<typename... _Args>
auto | _M_emplace (const_iterator __hint, std::false_type, _Args &&... __args) -> iterator
template<typename _Arg , typename _NodeGenerator >
auto | _M_insert (_Arg &&__v, const _NodeGenerator &__node_gen, true_type, size_type __n_elt) -> pair< iterator, bool >
template<typename _Arg , typename _NodeGenerator >
auto | _M_insert (const_iterator __hint, _Arg &&__v, const _NodeGenerator &__node_gen, false_type) -> iterator
iterator | begin () noexcept
const_iterator | begin () const noexcept
local_iterator | begin (size_type __n)
const_local_iterator | begin (size_type __n) const
size_type | bucket (const key_type &__k) const
size_type | bucket_count () const noexcept
size_type | bucket_size (size_type __n) const
const_iterator | cbegin () const noexcept
const_local_iterator | cbegin (size_type __n) const
const_iterator | cend () const noexcept
const_local_iterator | cend (size_type __n) 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
iterator | end () noexcept
const_iterator | end () const noexcept
local_iterator | end (size_type __n)
const_local_iterator | end (size_type __n) const
std::pair< iterator, iterator > | equal_range (const key_type &__k)
std::pair< const_iterator, const_iterator > | equal_range (const key_type &__k) const
iterator | erase (const_iterator)
iterator | erase (iterator __it)
size_type | erase (const key_type &__k)
iterator | erase (const_iterator, const_iterator)
iterator | find (const key_type &__k)
const_iterator | find (const key_type &__k) const
allocator_type | get_allocator () const noexcept
key_equal | key_eq () const
float | load_factor () const noexcept
size_type | max_bucket_count () const noexcept
size_type | max_size () const noexcept
_Hashtable & | operator= (const _Hashtable &__ht)
_Hashtable & | operator= (_Hashtable &&__ht) noexcept(__node_alloc_traits::_S_nothrow_move() &&is_nothrow_move_assignable< _H1 >::value &&is_nothrow_move_assignable< _Equal >::value)
_Hashtable & | operator= (initializer_list< value_type > __l)
void | rehash (size_type __n)
size_type | size () const noexcept
void | swap (_Hashtable &) noexcept(__and_< __is_nothrow_swappable< _H1 >, __is_nothrow_swappable< _Equal >>::value)

## Protected Member Functions

size_type | _M_bucket_index (__node_type *__n) const noexcept
size_type | _M_bucket_index (const key_type &__k, __hash_code __c) const
template<typename... _Args>
std::pair< iterator, bool > | _M_emplace (std::true_type, _Args &&... __args)
template<typename... _Args>
iterator | _M_emplace (std::false_type __uk, _Args &&... __args)
template<typename... _Args>
iterator | _M_emplace (const_iterator, std::true_type __uk, _Args &&... __args)
template<typename... _Args>
iterator | _M_emplace (const_iterator, std::false_type, _Args &&... __args)
const _Equal & | _M_eq () const
_Equal & | _M_eq ()
bool | _M_equals (const _Key &__k, __hash_code __c, __node_type *__n) const
size_type | _M_erase (std::true_type, const key_type &)
size_type | _M_erase (std::false_type, const key_type &)
iterator | _M_erase (size_type __bkt, __node_base *__prev_n, __node_type *__n)
__node_base * | _M_find_before_node (size_type, const key_type &, __hash_code) const
__node_type * | _M_find_node (size_type __bkt, const key_type &__key, __hash_code __c) const
__node_base * | _M_get_previous_node (size_type __bkt, __node_base *__n)
template<typename _Arg , typename _NodeGenerator >
std::pair< iterator, bool > | _M_insert (_Arg &&, const _NodeGenerator &, true_type, size_type=1)
template<typename _Arg , typename _NodeGenerator >
iterator | _M_insert (_Arg &&__arg, const _NodeGenerator &__node_gen, false_type __uk)
template<typename _Arg , typename _NodeGenerator >
iterator | _M_insert (const_iterator, _Arg &&__arg, const _NodeGenerator &__node_gen, true_type __uk)
template<typename _Arg , typename _NodeGenerator >
iterator | _M_insert (const_iterator, _Arg &&, const _NodeGenerator &, false_type)
void | _M_insert_bucket_begin (size_type, __node_type *)
iterator | _M_insert_multi_node (__node_type *__hint, __hash_code __code, __node_type *__n)
iterator | _M_insert_unique_node (size_type __bkt, __hash_code __code, __node_type *__n, size_type __n_elt=1)
void | _M_remove_bucket_begin (size_type __bkt, __node_type *__next_n, size_type __next_bkt)
void | _M_swap (_Hashtable_base &__x)

## Private Types

using | __bucket_alloc_traits = std::allocator_traits< __bucket_alloc_type >
using | __bucket_alloc_type = __alloc_rebind< __node_alloc_type, __bucket_type >

## Private Member Functions

__bucket_type * | _M_allocate_buckets (std::size_t __n)
__node_type * | _M_allocate_node (_Args &&... __args)
void | _M_deallocate_buckets (__bucket_type *, std::size_t __n)
void | _M_deallocate_node (__node_type *__n)
void | _M_deallocate_nodes (__node_type *__n)
__node_alloc_type & | _M_node_allocator ()
const __node_alloc_type & | _M_node_allocator () const

## Friends

template<typename _Keya , typename _Valuea , typename _Alloca , typename _ExtractKeya , typename _Equala , typename _H1a , typename _H2a , typename _Hasha , typename _RehashPolicya , typename _Traitsa , bool _Constant_iteratorsa>
struct | __detail::_Insert
template<typename _Keya , typename _Valuea , typename _Alloca , typename _ExtractKeya , typename _Equala , typename _H1a , typename _H2a , typename _Hasha , typename _RehashPolicya , typename _Traitsa >
struct | __detail::_Insert_base
template<typename _Keya , typename _Valuea , typename _Alloca , typename _ExtractKeya , typename _Equala , typename _H1a , typename _H2a , typename _Hasha , 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 _H1, typename _H2, typename _Hash, typename _RehashPolicy, typename _Traits>
class std::_Hashtable< _Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits >

Primary class template _Hashtable.

Template Parameters

  _Value | CopyConstructible type.
  _Key | CopyConstructible type.
  _Alloc | An allocator type ([lib.allocator.requirements]) whose _Alloc::value_type is _Value. As a conforming extension, we allow for _Alloc::value_type != _Value.
  _ExtractKey | Function object that takes an object of type _Value and returns a value of type _Key.
  _Equal | Function object that takes two objects of type k and returns a bool-like value that is true if the two objects are considered equal.
  _H1 | The 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()].
  _H2 | The 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).
  _Hash | The ranged hash function (Tavori and Dreizin). A binary function whose argument types are _Key and size_t and whose result type is size_t. Given arguments k and N, the return value is in the range [0, N). Default: hash(k, N) = h2(h1(k), N). If _Hash is anything other than the default, _H1 and _H2 are ignored.

  _RehashPolicy

  Policy 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. If so, returns make_pair(true, n), where n is the new bucket count. If not, returns make_pair(false, <anything>)

  _Traits | Compile-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* 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 173 of file bits/hashtable.h.

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

- bits/hashtable.h