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diff --git a/absl/container/flat_hash_map.h b/absl/container/flat_hash_map.h new file mode 100644 index 000000000000..13fbfba51f48 --- /dev/null +++ b/absl/container/flat_hash_map.h @@ -0,0 +1,528 @@ +// 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 +// +// http://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: flat_hash_map.h +// ----------------------------------------------------------------------------- +// +// An `absl::flat_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, +// `flat_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`. + +#ifndef ABSL_CONTAINER_FLAT_HASH_MAP_H_ +#define ABSL_CONTAINER_FLAT_HASH_MAP_H_ + +#include <cstddef> +#include <new> +#include <type_traits> +#include <utility> + +#include "absl/container/internal/container_memory.h" +#include "absl/container/internal/hash_function_defaults.h" // IWYU pragma: export +#include "absl/container/internal/raw_hash_map.h" // IWYU pragma: export +#include "absl/memory/memory.h" + +namespace absl { +namespace container_internal { +template <class K, class V> +struct FlatHashMapPolicy; +} // namespace container_internal + +// ----------------------------------------------------------------------------- +// absl::flat_hash_map +// ----------------------------------------------------------------------------- +// +// An `absl::flat_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: +// +// * Requires keys that are CopyConstructible +// * Requires values that are MoveConstructible +// * Supports heterogeneous lookup, through `find()`, `operator[]()` and +// `insert()`, provided that the map is provided a compatible heterogeneous +// hashing function and equality operator. +// * Invalidates any references and pointers to elements within the table after +// `rehash()`. +// * 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, `flat_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 `flat_hash_map`. +// If your type is not yet supported by the `asbl::Hash` framework, see +// absl/hash/hash.h for information on extending Abseil hashing to user-defined +// types. +// +// NOTE: A `flat_hash_map` stores its value types directly inside its +// implementation array to avoid memory indirection. Because a `flat_hash_map` +// is designed to move data when rehashed, map values will not retain pointer +// stability. If you require pointer stability, or your values are large, +// consider using `absl::flat_hash_map<Key, std::unique_ptr<Value>>` instead. +// If your types are not moveable or you require pointer stability for keys, +// consider `absl::node_hash_map`. +// +// Example: +// +// // Create a flat hash map of three strings (that map to strings) +// absl::flat_hash_map<std::string, std::string> ducks = +// {{"a", "huey"}, {"b", "dewey"}, {"c", "louie"}}; +// +// // Insert a new element into the flat hash map +// ducks.insert({"d", "donald"}}; +// +// // Force a rehash of the flat 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 K, class V, + class Hash = absl::container_internal::hash_default_hash<K>, + class Eq = absl::container_internal::hash_default_eq<K>, + class Allocator = std::allocator<std::pair<const K, V>>> +class flat_hash_map : public absl::container_internal::raw_hash_map< + absl::container_internal::FlatHashMapPolicy<K, V>, + Hash, Eq, Allocator> { + using Base = typename flat_hash_map::raw_hash_map; + + public: + flat_hash_map() {} + using Base::Base; + + // flat_hash_map::begin() + // + // Returns an iterator to the beginning of the `flat_hash_map`. + using Base::begin; + + // flat_hash_map::cbegin() + // + // Returns a const iterator to the beginning of the `flat_hash_map`. + using Base::cbegin; + + // flat_hash_map::cend() + // + // Returns a const iterator to the end of the `flat_hash_map`. + using Base::cend; + + // flat_hash_map::end() + // + // Returns an iterator to the end of the `flat_hash_map`. + using Base::end; + + // flat_hash_map::capacity() + // + // Returns the number of element slots (assigned, deleted, and empty) + // available within the `flat_hash_map`. + // + // NOTE: this member function is particular to `absl::flat_hash_map` and is + // not provided in the `std::unordered_map` API. + using Base::capacity; + + // flat_hash_map::empty() + // + // Returns whether or not the `flat_hash_map` is empty. + using Base::empty; + + // flat_hash_map::max_size() + // + // Returns the largest theoretical possible number of elements within a + // `flat_hash_map` under current memory constraints. This value can be thought + // of the largest value of `std::distance(begin(), end())` for a + // `flat_hash_map<K, V>`. + using Base::max_size; + + // flat_hash_map::size() + // + // Returns the number of elements currently within the `flat_hash_map`. + using Base::size; + + // flat_hash_map::clear() + // + // Removes all elements from the `flat_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; + + // flat_hash_map::erase() + // + // Erases elements within the `flat_hash_map`. Erasing does not trigger a + // rehash. Overloads are listed below. + // + // void erase(const_iterator pos): + // + // Erases the element at `position` of the `flat_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`. + // + // size_type erase(const key_type& key): + // + // Erases the element with the matching key, if it exists. + using Base::erase; + + // flat_hash_map::insert() + // + // Inserts an element of the specified value into the `flat_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 `flat_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 `flat_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. + // + // 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 `flat_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 + // `flat_hash_map` we guarantee the first match is inserted. + using Base::insert; + + // flat_hash_map::insert_or_assign() + // + // Inserts an element of the specified value into the `flat_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 existing iterators are invalidated. Overloads are + // listed below. + // + // pair<iterator, bool> insert_or_assign(const init_type& k, T&& obj): + // pair<iterator, bool> insert_or_assign(init_type&& k, T&& obj): + // + // Inserts/Assigns (or moves) the element of the specified key into the + // `flat_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 + // `flat_hash_map` using the position of `hint` as a non-binding suggestion + // for where to begin the insertion search. + using Base::insert_or_assign; + + // flat_hash_map::emplace() + // + // Inserts an element of the specified value by constructing it in-place + // within the `flat_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; + + // flat_hash_map::emplace_hint() + // + // Inserts an element of the specified value by constructing it in-place + // within the `flat_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; + + // flat_hash_map::try_emplace() + // + // Inserts an element of the specified value by constructing it in-place + // within the `flat_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. + // + // pair<iterator, bool> try_emplace(const key_type& k, Args&&... args): + // pair<iterator, bool> try_emplace(key_type&& k, Args&&... args): + // + // Inserts (via copy or move) the element of the specified key into the + // `flat_hash_map`. + // + // iterator try_emplace(const_iterator hint, + // const init_type& k, Args&&... args): + // iterator try_emplace(const_iterator hint, init_type&& k, Args&&... args): + // + // Inserts (via copy or move) the element of the specified key into the + // `flat_hash_map` using the position of `hint` as a non-binding suggestion + // for where to begin the insertion search. + using Base::try_emplace; + + // flat_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 + // `flat_hash_map` does not contain an element with a matching key, this + // function returns an empty node handle. + using Base::extract; + + // flat_hash_map::merge() + // + // Extracts elements from a given `source` flat hash map into this + // `flat_hash_map`. If the destination `flat_hash_map` already contains an + // element with an equivalent key, that element is not extracted. + using Base::merge; + + // flat_hash_map::swap(flat_hash_map& other) + // + // Exchanges the contents of this `flat_hash_map` with those of the `other` + // flat hash map, avoiding invocation of any move, copy, or swap operations on + // individual elements. + // + // All iterators and references on the `flat_hash_map` remain valid, excepting + // for the past-the-end iterator, which is invalidated. + // + // `swap()` requires that the flat hash map's hashing and key equivalence + // functions be Swappable, and are exchaged 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; + + // flat_hash_map::rehash(count) + // + // Rehashes the `flat_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). + // + // NOTE: unlike behavior in `std::unordered_map`, references are also + // invalidated upon a `rehash()`. + using Base::rehash; + + // flat_hash_map::reserve(count) + // + // Sets the number of slots in the `flat_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; + + // flat_hash_map::at() + // + // Returns a reference to the mapped value of the element with key equivalent + // to the passed key. + using Base::at; + + // flat_hash_map::contains() + // + // Determines whether an element with a key comparing equal to the given `key` + // exists within the `flat_hash_map`, returning `true` if so or `false` + // otherwise. + using Base::contains; + + // flat_hash_map::count(const Key& key) const + // + // Returns the number of elements with a key comparing equal to the given + // `key` within the `flat_hash_map`. note that this function will return + // either `1` or `0` since duplicate keys are not allowed within a + // `flat_hash_map`. + using Base::count; + + // flat_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 + // `flat_hash_map`. + using Base::equal_range; + + // flat_hash_map::find() + // + // Finds an element with the passed `key` within the `flat_hash_map`. + using Base::find; + + // flat_hash_map::operator[]() + // + // Returns a reference to the value mapped to the passed key within the + // `flat_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[]; + + // flat_hash_map::bucket_count() + // + // Returns the number of "buckets" within the `flat_hash_map`. Note that + // because a flat hash map contains all elements within its internal storage, + // this value simply equals the current capacity of the `flat_hash_map`. + using Base::bucket_count; + + // flat_hash_map::load_factor() + // + // Returns the current load factor of the `flat_hash_map` (the average number + // of slots occupied with a value within the hash map). + using Base::load_factor; + + // flat_hash_map::max_load_factor() + // + // Manages the maximum load factor of the `flat_hash_map`. Overloads are + // listed below. + // + // float flat_hash_map::max_load_factor() + // + // Returns the current maximum load factor of the `flat_hash_map`. + // + // void flat_hash_map::max_load_factor(float ml) + // + // Sets the maximum load factor of the `flat_hash_map` to the passed value. + // + // NOTE: This overload is provided only for API compatibility with the STL; + // `flat_hash_map` will ignore any set load factor and manage its rehashing + // internally as an implementation detail. + using Base::max_load_factor; + + // flat_hash_map::get_allocator() + // + // Returns the allocator function associated with this `flat_hash_map`. + using Base::get_allocator; + + // flat_hash_map::hash_function() + // + // Returns the hashing function used to hash the keys within this + // `flat_hash_map`. + using Base::hash_function; + + // flat_hash_map::key_eq() + // + // Returns the function used for comparing keys equality. + using Base::key_eq; +}; + +namespace container_internal { + +template <class K, class V> +struct FlatHashMapPolicy { + using slot_type = container_internal::slot_type<K, V>; + using key_type = K; + using mapped_type = V; + using init_type = std::pair</*non const*/ key_type, mapped_type>; + + template <class Allocator, class... Args> + static void construct(Allocator* alloc, slot_type* slot, Args&&... args) { + slot_type::construct(alloc, slot, std::forward<Args>(args)...); + } + + template <class Allocator> + static void destroy(Allocator* alloc, slot_type* slot) { + slot_type::destroy(alloc, slot); + } + + template <class Allocator> + static void transfer(Allocator* alloc, slot_type* new_slot, + slot_type* old_slot) { + slot_type::transfer(alloc, new_slot, old_slot); + } + + 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 space_used(const slot_type*) { return 0; } + + static std::pair<const K, V>& element(slot_type* slot) { return slot->value; } + + static V& value(std::pair<const K, V>* kv) { return kv->second; } + static const V& value(const std::pair<const K, V>* kv) { return kv->second; } +}; + +} // namespace container_internal +} // namespace absl +#endif // ABSL_CONTAINER_FLAT_HASH_MAP_H_ |