// 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. // // `node_hash_map` is not exception-safe. #ifndef ABSL_CONTAINER_NODE_HASH_MAP_H_ #define ABSL_CONTAINER_NODE_HASH_MAP_H_ #include <cstddef> #include <memory> #include <type_traits> #include <utility> #include "absl/algorithm/container.h" #include "absl/base/attributes.h" #include "absl/container/hash_container_defaults.h" #include "absl/container/internal/container_memory.h" #include "absl/container/internal/node_slot_policy.h" #include "absl/container/internal/raw_hash_map.h" // IWYU pragma: export #include "absl/memory/memory.h" #include "absl/meta/type_traits.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. See below for details. // * 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. // // To achieve heterogeneous lookup for custom types either `Hash` and `Eq` type // parameters can be used or `T` should have public inner types // `absl_container_hash` and (optionally) `absl_container_eq`. In either case, // `typename Hash::is_transparent` and `typename Eq::is_transparent` should be // well-formed. Both types are basically functors: // * `Hash` should support `size_t operator()(U val) const` that returns a hash // for the given `val`. // * `Eq` should support `bool operator()(U lhs, V rhs) const` that returns true // if `lhs` is equal to `rhs`. // // In most cases `T` needs only to provide the `absl_container_hash`. In this // case `std::equal_to<void>` will be used instead of `eq` part. // // 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 = DefaultHashContainerHash<Key>, class Eq = DefaultHashContainerEq<Key>, class Alloc = std::allocator<std::pair<const Key, Value>>> class ABSL_ATTRIBUTE_OWNER 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. // // 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) { … } // swap(node_hash_map<>, node_hash_map<>) // // Swaps the contents of two `node_hash_map` containers. // // NOTE: we need to define this function template in order for // `flat_hash_set::swap` to be called instead of `std::swap`. Even though we // have `swap(raw_hash_set&, raw_hash_set&)` defined, that function requires a // derived-to-base conversion, whereas `std::swap` is a function template so // `std::swap` will be preferred by compiler. template <typename K, typename V, typename H, typename E, typename A> void swap(node_hash_map<K, V, H, E, A>& x, node_hash_map<K, V, H, E, A>& y) noexcept(noexcept(x.swap(y))) { … } namespace container_internal { // c_for_each_fast(node_hash_map<>, Function) // // Container-based version of the <algorithm> `std::for_each()` function to // apply a function to a container's elements. // There is no guarantees on the order of the function calls. // Erasure and/or insertion of elements in the function is not allowed. template <typename K, typename V, typename H, typename E, typename A, typename Function> decay_t<Function> c_for_each_fast(const node_hash_map<K, V, H, E, A>& c, Function&& f) { … } template <typename K, typename V, typename H, typename E, typename A, typename Function> decay_t<Function> c_for_each_fast(node_hash_map<K, V, H, E, A>& c, Function&& f) { … } template <typename K, typename V, typename H, typename E, typename A, typename Function> decay_t<Function> c_for_each_fast(node_hash_map<K, V, H, E, A>&& c, Function&& f) { … } } // namespace container_internal 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>> { … }; } // namespace container_internal namespace container_algorithm_internal { // Specialization of trait in absl/algorithm/container.h IsUnorderedContainer<absl::node_hash_map<Key, T, Hash, KeyEqual, Allocator>>; } // namespace container_algorithm_internal ABSL_NAMESPACE_END } // namespace absl #endif // ABSL_CONTAINER_NODE_HASH_MAP_H_
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