node_hash_map.h - mozsearch

// Copyright 2018 The Abseil Authors.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//      https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

//

// -----------------------------------------------------------------------------

// File: node_hash_map.h

// -----------------------------------------------------------------------------

//

// An `absl::node_hash_map<K, V>` is an unordered associative container of

// unique keys and associated values designed to be a more efficient replacement

// for `std::unordered_map`. Like `unordered_map`, search, insertion, and

// deletion of map elements can be done as an `O(1)` operation. However,

// `node_hash_map` (and other unordered associative containers known as the

// collection of Abseil "Swiss tables") contain other optimizations that result

// in both memory and computation advantages.

//

// In most cases, your default choice for a hash map should be a map of type

// `flat_hash_map`. However, if you need pointer stability and cannot store

// a `flat_hash_map` with `unique_ptr` elements, a `node_hash_map` may be a

// valid alternative. As well, if you are migrating your code from using

// `std::unordered_map`, a `node_hash_map` provides a more straightforward

// migration, because it guarantees pointer stability. Consider migrating to

// `node_hash_map` and perhaps converting to a more efficient `flat_hash_map`

// upon further review.

#ifndef ABSL_CONTAINER_NODE_HASH_MAP_H_

#define ABSL_CONTAINER_NODE_HASH_MAP_H_

#include <tuple>

#include <type_traits>

#include <utility>

#include "absl/algorithm/container.h"

#include "absl/base/macros.h"

#include "absl/container/internal/container_memory.h"

#include "absl/container/internal/hash_function_defaults.h"  // IWYU pragma: export

#include "absl/container/internal/node_slot_policy.h"

#include "absl/container/internal/raw_hash_map.h"  // IWYU pragma: export

#include "absl/memory/memory.h"

namespace absl {

ABSL_NAMESPACE_BEGIN

namespace container_internal {

template <class Key, class Value>

class NodeHashMapPolicy;

}  // namespace container_internal

// -----------------------------------------------------------------------------

// absl::node_hash_map

// -----------------------------------------------------------------------------

//

// An `absl::node_hash_map<K, V>` is an unordered associative container which

// has been optimized for both speed and memory footprint in most common use

// cases. Its interface is similar to that of `std::unordered_map<K, V>` with

// the following notable differences:

//

// * Supports heterogeneous lookup, through `find()`, `operator[]()` and

//   `insert()`, provided that the map is provided a compatible heterogeneous

//   hashing function and equality operator.

// * Contains a `capacity()` member function indicating the number of element

//   slots (open, deleted, and empty) within the hash map.

// * Returns `void` from the `erase(iterator)` overload.

//

// By default, `node_hash_map` uses the `absl::Hash` hashing framework.

// All fundamental and Abseil types that support the `absl::Hash` framework have

// a compatible equality operator for comparing insertions into `node_hash_map`.

// If your type is not yet supported by the `absl::Hash` framework, see

// absl/hash/hash.h for information on extending Abseil hashing to user-defined

// types.

//

// Using `absl::node_hash_map` at interface boundaries in dynamically loaded

// libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may

// be randomized across dynamically loaded libraries.

//

// Example:

//

//   // Create a node hash map of three strings (that map to strings)

//   absl::node_hash_map<std::string, std::string> ducks =

//     {{"a", "huey"}, {"b", "dewey"}, {"c", "louie"}};

//

//  // Insert a new element into the node hash map

//  ducks.insert({"d", "donald"}};

//

//  // Force a rehash of the node hash map

//  ducks.rehash(0);

//

//  // Find the element with the key "b"

//  std::string search_key = "b";

//  auto result = ducks.find(search_key);

//  if (result != ducks.end()) {

//    std::cout << "Result: " << result->second << std::endl;

//  }

template <class Key, class Value,

          class Hash = absl::container_internal::hash_default_hash<Key>,

          class Eq = absl::container_internal::hash_default_eq<Key>,

          class Alloc = std::allocator<std::pair<const Key, Value>>>

class node_hash_map

    : public absl::container_internal::raw_hash_map<

          absl::container_internal::NodeHashMapPolicy<Key, Value>, Hash, Eq,

          Alloc> {

  using Base = typename node_hash_map::raw_hash_map;

 public:

  // Constructors and Assignment Operators

//

  // A node_hash_map supports the same overload set as `std::unordered_map`

  // for construction and assignment:

//

  // *  Default constructor

//

  //    // No allocation for the table's elements is made.

  //    absl::node_hash_map<int, std::string> map1;

//

  // * Initializer List constructor

//

  //   absl::node_hash_map<int, std::string> map2 =

  //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};

//

  // * Copy constructor

//

  //   absl::node_hash_map<int, std::string> map3(map2);

//

  // * Copy assignment operator

//

  //  // Hash functor and Comparator are copied as well

  //  absl::node_hash_map<int, std::string> map4;

  //  map4 = map3;

//

  // * Move constructor

//

  //   // Move is guaranteed efficient

  //   absl::node_hash_map<int, std::string> map5(std::move(map4));

//

  // * Move assignment operator

//

  //   // May be efficient if allocators are compatible

  //   absl::node_hash_map<int, std::string> map6;

  //   map6 = std::move(map5);

//

  // * Range constructor

//

  //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};

  //   absl::node_hash_map<int, std::string> map7(v.begin(), v.end());

  node_hash_map() {}

  using Base::Base;

  // node_hash_map::begin()

//

  // Returns an iterator to the beginning of the `node_hash_map`.

  using Base::begin;

  // node_hash_map::cbegin()

//

  // Returns a const iterator to the beginning of the `node_hash_map`.

  using Base::cbegin;

  // node_hash_map::cend()

//

  // Returns a const iterator to the end of the `node_hash_map`.

  using Base::cend;

  // node_hash_map::end()

//

  // Returns an iterator to the end of the `node_hash_map`.

  using Base::end;

  // node_hash_map::capacity()

//

  // Returns the number of element slots (assigned, deleted, and empty)

  // available within the `node_hash_map`.

//

  // NOTE: this member function is particular to `absl::node_hash_map` and is

  // not provided in the `std::unordered_map` API.

  using Base::capacity;

  // node_hash_map::empty()

//

  // Returns whether or not the `node_hash_map` is empty.

  using Base::empty;

  // node_hash_map::max_size()

//

  // Returns the largest theoretical possible number of elements within a

  // `node_hash_map` under current memory constraints. This value can be thought

  // of as the largest value of `std::distance(begin(), end())` for a

  // `node_hash_map<K, V>`.

  using Base::max_size;

  // node_hash_map::size()

//

  // Returns the number of elements currently within the `node_hash_map`.

  using Base::size;

  // node_hash_map::clear()

//

  // Removes all elements from the `node_hash_map`. Invalidates any references,

  // pointers, or iterators referring to contained elements.

//

  // NOTE: this operation may shrink the underlying buffer. To avoid shrinking

  // the underlying buffer call `erase(begin(), end())`.

  using Base::clear;

  // node_hash_map::erase()

//

  // Erases elements within the `node_hash_map`. Erasing does not trigger a

  // rehash. Overloads are listed below.

//

  // void erase(const_iterator pos):

//

  //   Erases the element at `position` of the `node_hash_map`, returning

  //   `void`.

//

  //   NOTE: this return behavior is different than that of STL containers in

  //   general and `std::unordered_map` in particular.

//

  // iterator erase(const_iterator first, const_iterator last):

//

  //   Erases the elements in the open interval [`first`, `last`), returning an

  //   iterator pointing to `last`. The special case of calling

  //   `erase(begin(), end())` resets the reserved growth such that if

  //   `reserve(N)` has previously been called and there has been no intervening

  //   call to `clear()`, then after calling `erase(begin(), end())`, it is safe

  //   to assume that inserting N elements will not cause a rehash.

//

  // size_type erase(const key_type& key):

//

  //   Erases the element with the matching key, if it exists, returning the

  //   number of elements erased (0 or 1).

  using Base::erase;

  // node_hash_map::insert()

//

  // Inserts an element of the specified value into the `node_hash_map`,

  // returning an iterator pointing to the newly inserted element, provided that

  // an element with the given key does not already exist. If rehashing occurs

  // due to the insertion, all iterators are invalidated. Overloads are listed

  // below.

//

  // std::pair<iterator,bool> insert(const init_type& value):

//

  //   Inserts a value into the `node_hash_map`. Returns a pair consisting of an

  //   iterator to the inserted element (or to the element that prevented the

  //   insertion) and a `bool` denoting whether the insertion took place.

//

  // std::pair<iterator,bool> insert(T&& value):

  // std::pair<iterator,bool> insert(init_type&& value):

//

  //   Inserts a moveable value into the `node_hash_map`. Returns a `std::pair`

  //   consisting of an iterator to the inserted element (or to the element that

  //   prevented the insertion) and a `bool` denoting whether the insertion took

  //   place.

//

  // iterator insert(const_iterator hint, const init_type& value):

  // iterator insert(const_iterator hint, T&& value):

  // iterator insert(const_iterator hint, init_type&& value);

//

  //   Inserts a value, using the position of `hint` as a non-binding suggestion

  //   for where to begin the insertion search. Returns an iterator to the

  //   inserted element, or to the existing element that prevented the

  //   insertion.

//

  // void insert(InputIterator first, InputIterator last):

//

  //   Inserts a range of values [`first`, `last`).

//

  //   NOTE: Although the STL does not specify which element may be inserted if

  //   multiple keys compare equivalently, for `node_hash_map` we guarantee the

  //   first match is inserted.

//

  // void insert(std::initializer_list<init_type> ilist):

//

  //   Inserts the elements within the initializer list `ilist`.

//

  //   NOTE: Although the STL does not specify which element may be inserted if

  //   multiple keys compare equivalently within the initializer list, for

  //   `node_hash_map` we guarantee the first match is inserted.

  using Base::insert;

  // node_hash_map::insert_or_assign()

//

  // Inserts an element of the specified value into the `node_hash_map` provided

  // that a value with the given key does not already exist, or replaces it with

  // the element value if a key for that value already exists, returning an

  // iterator pointing to the newly inserted element. If rehashing occurs due to

  // the insertion, all iterators are invalidated. Overloads are listed

  // below.

//

  // std::pair<iterator, bool> insert_or_assign(const init_type& k, T&& obj):

  // std::pair<iterator, bool> insert_or_assign(init_type&& k, T&& obj):

//

  //   Inserts/Assigns (or moves) the element of the specified key into the

  //   `node_hash_map`.

//

  // iterator insert_or_assign(const_iterator hint,

  //                           const init_type& k, T&& obj):

  // iterator insert_or_assign(const_iterator hint, init_type&& k, T&& obj):

//

  //   Inserts/Assigns (or moves) the element of the specified key into the

  //   `node_hash_map` using the position of `hint` as a non-binding suggestion

  //   for where to begin the insertion search.

  using Base::insert_or_assign;

  // node_hash_map::emplace()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `node_hash_map`, provided that no element with the given key

  // already exists.

//

  // The element may be constructed even if there already is an element with the

  // key in the container, in which case the newly constructed element will be

  // destroyed immediately. Prefer `try_emplace()` unless your key is not

  // copyable or moveable.

//

  // If rehashing occurs due to the insertion, all iterators are invalidated.

  using Base::emplace;

  // node_hash_map::emplace_hint()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `node_hash_map`, using the position of `hint` as a non-binding

  // suggestion for where to begin the insertion search, and only inserts

  // provided that no element with the given key already exists.

//

  // The element may be constructed even if there already is an element with the

  // key in the container, in which case the newly constructed element will be

  // destroyed immediately. Prefer `try_emplace()` unless your key is not

  // copyable or moveable.

//

  // If rehashing occurs due to the insertion, all iterators are invalidated.

  using Base::emplace_hint;

  // node_hash_map::try_emplace()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `node_hash_map`, provided that no element with the given key

  // already exists. Unlike `emplace()`, if an element with the given key

  // already exists, we guarantee that no element is constructed.

//

  // If rehashing occurs due to the insertion, all iterators are invalidated.

  // Overloads are listed below.

//

  //   std::pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):

  //   std::pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):

//

  // Inserts (via copy or move) the element of the specified key into the

  // `node_hash_map`.

//

  //   iterator try_emplace(const_iterator hint,

  //                        const key_type& k, Args&&... args):

  //   iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args):

//

  // Inserts (via copy or move) the element of the specified key into the

  // `node_hash_map` using the position of `hint` as a non-binding suggestion

  // for where to begin the insertion search.

//

  // All `try_emplace()` overloads make the same guarantees regarding rvalue

  // arguments as `std::unordered_map::try_emplace()`, namely that these

  // functions will not move from rvalue arguments if insertions do not happen.

  using Base::try_emplace;

  // node_hash_map::extract()

//

  // Extracts the indicated element, erasing it in the process, and returns it

  // as a C++17-compatible node handle. Overloads are listed below.

//

  // node_type extract(const_iterator position):

//

  //   Extracts the key,value pair of the element at the indicated position and

  //   returns a node handle owning that extracted data.

//

  // node_type extract(const key_type& x):

//

  //   Extracts the key,value pair of the element with a key matching the passed

  //   key value and returns a node handle owning that extracted data. If the

  //   `node_hash_map` does not contain an element with a matching key, this

  //   function returns an empty node handle.

//

  // NOTE: when compiled in an earlier version of C++ than C++17,

  // `node_type::key()` returns a const reference to the key instead of a

  // mutable reference. We cannot safely return a mutable reference without

  // std::launder (which is not available before C++17).

  using Base::extract;

  // node_hash_map::merge()

//

  // Extracts elements from a given `source` node hash map into this

  // `node_hash_map`. If the destination `node_hash_map` already contains an

  // element with an equivalent key, that element is not extracted.

  using Base::merge;

  // node_hash_map::swap(node_hash_map& other)

//

  // Exchanges the contents of this `node_hash_map` with those of the `other`

  // node hash map, avoiding invocation of any move, copy, or swap operations on

  // individual elements.

//

  // All iterators and references on the `node_hash_map` remain valid, excepting

  // for the past-the-end iterator, which is invalidated.

//

  // `swap()` requires that the node hash map's hashing and key equivalence

  // functions be Swappable, and are exchanged using unqualified calls to

  // non-member `swap()`. If the map's allocator has

  // `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`

  // set to `true`, the allocators are also exchanged using an unqualified call

  // to non-member `swap()`; otherwise, the allocators are not swapped.

  using Base::swap;

  // node_hash_map::rehash(count)

//

  // Rehashes the `node_hash_map`, setting the number of slots to be at least

  // the passed value. If the new number of slots increases the load factor more

  // than the current maximum load factor

  // (`count` < `size()` / `max_load_factor()`), then the new number of slots

  // will be at least `size()` / `max_load_factor()`.

//

  // To force a rehash, pass rehash(0).

  using Base::rehash;

  // node_hash_map::reserve(count)

//

  // Sets the number of slots in the `node_hash_map` to the number needed to

  // accommodate at least `count` total elements without exceeding the current

  // maximum load factor, and may rehash the container if needed.

  using Base::reserve;

  // node_hash_map::at()

//

  // Returns a reference to the mapped value of the element with key equivalent

  // to the passed key.

  using Base::at;

  // node_hash_map::contains()

//

  // Determines whether an element with a key comparing equal to the given `key`

  // exists within the `node_hash_map`, returning `true` if so or `false`

  // otherwise.

  using Base::contains;

  // node_hash_map::count(const Key& key) const

//

  // Returns the number of elements with a key comparing equal to the given

  // `key` within the `node_hash_map`. note that this function will return

  // either `1` or `0` since duplicate keys are not allowed within a

  // `node_hash_map`.

  using Base::count;

  // node_hash_map::equal_range()

//

  // Returns a closed range [first, last], defined by a `std::pair` of two

  // iterators, containing all elements with the passed key in the

  // `node_hash_map`.

  using Base::equal_range;

  // node_hash_map::find()

//

  // Finds an element with the passed `key` within the `node_hash_map`.

  using Base::find;

  // node_hash_map::operator[]()

//

  // Returns a reference to the value mapped to the passed key within the

  // `node_hash_map`, performing an `insert()` if the key does not already

  // exist. If an insertion occurs and results in a rehashing of the container,

  // all iterators are invalidated. Otherwise iterators are not affected and

  // references are not invalidated. Overloads are listed below.

//

  // T& operator[](const Key& key):

//

  //   Inserts an init_type object constructed in-place if the element with the

  //   given key does not exist.

//

  // T& operator[](Key&& key):

//

  //   Inserts an init_type object constructed in-place provided that an element

  //   with the given key does not exist.

  using Base::operator[];

  // node_hash_map::bucket_count()

//

  // Returns the number of "buckets" within the `node_hash_map`.

  using Base::bucket_count;

  // node_hash_map::load_factor()

//

  // Returns the current load factor of the `node_hash_map` (the average number

  // of slots occupied with a value within the hash map).

  using Base::load_factor;

  // node_hash_map::max_load_factor()

//

  // Manages the maximum load factor of the `node_hash_map`. Overloads are

  // listed below.

//

  // float node_hash_map::max_load_factor()

//

  //   Returns the current maximum load factor of the `node_hash_map`.

//

  // void node_hash_map::max_load_factor(float ml)

//

  //   Sets the maximum load factor of the `node_hash_map` to the passed value.

//

  //   NOTE: This overload is provided only for API compatibility with the STL;

  //   `node_hash_map` will ignore any set load factor and manage its rehashing

  //   internally as an implementation detail.

  using Base::max_load_factor;

  // node_hash_map::get_allocator()

//

  // Returns the allocator function associated with this `node_hash_map`.

  using Base::get_allocator;

  // node_hash_map::hash_function()

//

  // Returns the hashing function used to hash the keys within this

  // `node_hash_map`.

  using Base::hash_function;

  // node_hash_map::key_eq()

//

  // Returns the function used for comparing keys equality.

  using Base::key_eq;

};

// erase_if(node_hash_map<>, Pred)

//

// Erases all elements that satisfy the predicate `pred` from the container `c`.

// Returns the number of erased elements.

template <typename K, typename V, typename H, typename E, typename A,

          typename Predicate>

typename node_hash_map<K, V, H, E, A>::size_type erase_if(

    node_hash_map<K, V, H, E, A>& c, Predicate pred) {

  return container_internal::EraseIf(pred, &c);

namespace container_internal {

template <class Key, class Value>

class NodeHashMapPolicy

    : public absl::container_internal::node_slot_policy<

          std::pair<const Key, Value>&, NodeHashMapPolicy<Key, Value>> {

  using value_type = std::pair<const Key, Value>;

 public:

  using key_type = Key;

  using mapped_type = Value;

  using init_type = std::pair</*non const*/ key_type, mapped_type>;

  template <class Allocator, class... Args>

  static value_type* new_element(Allocator* alloc, Args&&... args) {

    using PairAlloc = typename absl::allocator_traits<

        Allocator>::template rebind_alloc<value_type>;

    PairAlloc pair_alloc(*alloc);

    value_type* res =

        absl::allocator_traits<PairAlloc>::allocate(pair_alloc, 1);

    absl::allocator_traits<PairAlloc>::construct(pair_alloc, res,

                                                 std::forward<Args>(args)...);

    return res;

  template <class Allocator>

  static void delete_element(Allocator* alloc, value_type* pair) {

    using PairAlloc = typename absl::allocator_traits<

        Allocator>::template rebind_alloc<value_type>;

    PairAlloc pair_alloc(*alloc);

    absl::allocator_traits<PairAlloc>::destroy(pair_alloc, pair);

    absl::allocator_traits<PairAlloc>::deallocate(pair_alloc, pair, 1);

  template <class F, class... Args>

  static decltype(absl::container_internal::DecomposePair(

      std::declval<F>(), std::declval<Args>()...))

  apply(F&& f, Args&&... args) {

    return absl::container_internal::DecomposePair(std::forward<F>(f),

                                                   std::forward<Args>(args)...);

  static size_t element_space_used(const value_type*) {

    return sizeof(value_type);

  static Value& value(value_type* elem) { return elem->second; }

  static const Value& value(const value_type* elem) { return elem->second; }

};

}  // namespace container_internal

namespace container_algorithm_internal {

// Specialization of trait in absl/algorithm/container.h

template <class Key, class T, class Hash, class KeyEqual, class Allocator>

struct IsUnorderedContainer<

    absl::node_hash_map<Key, T, Hash, KeyEqual, Allocator>> : std::true_type {};

}  // namespace container_algorithm_internal

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_CONTAINER_NODE_HASH_MAP_H_

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