| // 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: flat_hash_set.h |
| // ----------------------------------------------------------------------------- |
| // |
| // An `absl::flat_hash_set<T>` is an unordered associative container designed to |
| // be a more efficient replacement for `std::unordered_set`. Like |
| // `unordered_set`, search, insertion, and deletion of set elements can be done |
| // as an `O(1)` operation. However, `flat_hash_set` (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 set should be a set of type |
| // `flat_hash_set`. |
| #ifndef ABSL_CONTAINER_FLAT_HASH_SET_H_ |
| #define ABSL_CONTAINER_FLAT_HASH_SET_H_ |
| |
| #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/raw_hash_set.h" // IWYU pragma: export |
| #include "absl/memory/memory.h" |
| |
| namespace absl { |
| ABSL_NAMESPACE_BEGIN |
| namespace container_internal { |
| template <typename T> |
| struct FlatHashSetPolicy; |
| } // namespace container_internal |
| |
| // ----------------------------------------------------------------------------- |
| // absl::flat_hash_set |
| // ----------------------------------------------------------------------------- |
| // |
| // An `absl::flat_hash_set<T>` 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_set<T>` with the |
| // following notable differences: |
| // |
| // * Requires keys that are CopyConstructible |
| // * Supports heterogeneous lookup, through `find()` and `insert()`, provided |
| // that the set 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 set. |
| // * Returns `void` from the `erase(iterator)` overload. |
| // |
| // By default, `flat_hash_set` 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_set`. |
| // 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::flat_hash_set` 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. |
| // |
| // NOTE: A `flat_hash_set` stores its keys directly inside its implementation |
| // array to avoid memory indirection. Because a `flat_hash_set` is designed to |
| // move data when rehashed, set keys will not retain pointer stability. If you |
| // require pointer stability, consider using |
| // `absl::flat_hash_set<std::unique_ptr<T>>`. If your type is not moveable and |
| // you require pointer stability, consider `absl::node_hash_set` instead. |
| // |
| // Example: |
| // |
| // // Create a flat hash set of three strings |
| // absl::flat_hash_set<std::string> ducks = |
| // {"huey", "dewey", "louie"}; |
| // |
| // // Insert a new element into the flat hash set |
| // ducks.insert("donald"); |
| // |
| // // Force a rehash of the flat hash set |
| // ducks.rehash(0); |
| // |
| // // See if "dewey" is present |
| // if (ducks.contains("dewey")) { |
| // std::cout << "We found dewey!" << std::endl; |
| // } |
| template <class T, class Hash = absl::container_internal::hash_default_hash<T>, |
| class Eq = absl::container_internal::hash_default_eq<T>, |
| class Allocator = std::allocator<T>> |
| class flat_hash_set |
| : public absl::container_internal::raw_hash_set< |
| absl::container_internal::FlatHashSetPolicy<T>, Hash, Eq, Allocator> { |
| using Base = typename flat_hash_set::raw_hash_set; |
| |
| public: |
| // Constructors and Assignment Operators |
| // |
| // A flat_hash_set supports the same overload set as `std::unordered_set` |
| // for construction and assignment: |
| // |
| // * Default constructor |
| // |
| // // No allocation for the table's elements is made. |
| // absl::flat_hash_set<std::string> set1; |
| // |
| // * Initializer List constructor |
| // |
| // absl::flat_hash_set<std::string> set2 = |
| // {{"huey"}, {"dewey"}, {"louie"},}; |
| // |
| // * Copy constructor |
| // |
| // absl::flat_hash_set<std::string> set3(set2); |
| // |
| // * Copy assignment operator |
| // |
| // // Hash functor and Comparator are copied as well |
| // absl::flat_hash_set<std::string> set4; |
| // set4 = set3; |
| // |
| // * Move constructor |
| // |
| // // Move is guaranteed efficient |
| // absl::flat_hash_set<std::string> set5(std::move(set4)); |
| // |
| // * Move assignment operator |
| // |
| // // May be efficient if allocators are compatible |
| // absl::flat_hash_set<std::string> set6; |
| // set6 = std::move(set5); |
| // |
| // * Range constructor |
| // |
| // std::vector<std::string> v = {"a", "b"}; |
| // absl::flat_hash_set<std::string> set7(v.begin(), v.end()); |
| flat_hash_set() {} |
| using Base::Base; |
| |
| // flat_hash_set::begin() |
| // |
| // Returns an iterator to the beginning of the `flat_hash_set`. |
| using Base::begin; |
| |
| // flat_hash_set::cbegin() |
| // |
| // Returns a const iterator to the beginning of the `flat_hash_set`. |
| using Base::cbegin; |
| |
| // flat_hash_set::cend() |
| // |
| // Returns a const iterator to the end of the `flat_hash_set`. |
| using Base::cend; |
| |
| // flat_hash_set::end() |
| // |
| // Returns an iterator to the end of the `flat_hash_set`. |
| using Base::end; |
| |
| // flat_hash_set::capacity() |
| // |
| // Returns the number of element slots (assigned, deleted, and empty) |
| // available within the `flat_hash_set`. |
| // |
| // NOTE: this member function is particular to `absl::flat_hash_set` and is |
| // not provided in the `std::unordered_set` API. |
| using Base::capacity; |
| |
| // flat_hash_set::empty() |
| // |
| // Returns whether or not the `flat_hash_set` is empty. |
| using Base::empty; |
| |
| // flat_hash_set::max_size() |
| // |
| // Returns the largest theoretical possible number of elements within a |
| // `flat_hash_set` under current memory constraints. This value can be thought |
| // of the largest value of `std::distance(begin(), end())` for a |
| // `flat_hash_set<T>`. |
| using Base::max_size; |
| |
| // flat_hash_set::size() |
| // |
| // Returns the number of elements currently within the `flat_hash_set`. |
| using Base::size; |
| |
| // flat_hash_set::clear() |
| // |
| // Removes all elements from the `flat_hash_set`. 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_set::erase() |
| // |
| // Erases elements within the `flat_hash_set`. Erasing does not trigger a |
| // rehash. Overloads are listed below. |
| // |
| // void erase(const_iterator pos): |
| // |
| // Erases the element at `position` of the `flat_hash_set`, returning |
| // `void`. |
| // |
| // NOTE: returning `void` in this case is different than that of STL |
| // containers in general and `std::unordered_set` in particular (which |
| // return an iterator to the element following the erased element). If that |
| // iterator is needed, simply post increment the iterator: |
| // |
| // set.erase(it++); |
| // |
| // 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, returning the |
| // number of elements erased (0 or 1). |
| using Base::erase; |
| |
| // flat_hash_set::insert() |
| // |
| // Inserts an element of the specified value into the `flat_hash_set`, |
| // 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 T& value): |
| // |
| // Inserts a value into the `flat_hash_set`. 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): |
| // |
| // Inserts a moveable value into the `flat_hash_set`. 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 T& value): |
| // iterator insert(const_iterator hint, T&& 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_set` we guarantee the |
| // first match is inserted. |
| // |
| // void insert(std::initializer_list<T> 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_set` we guarantee the first match is inserted. |
| using Base::insert; |
| |
| // flat_hash_set::emplace() |
| // |
| // Inserts an element of the specified value by constructing it in-place |
| // within the `flat_hash_set`, 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. |
| // |
| // If rehashing occurs due to the insertion, all iterators are invalidated. |
| using Base::emplace; |
| |
| // flat_hash_set::emplace_hint() |
| // |
| // Inserts an element of the specified value by constructing it in-place |
| // within the `flat_hash_set`, 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. |
| // |
| // If rehashing occurs due to the insertion, all iterators are invalidated. |
| using Base::emplace_hint; |
| |
| // flat_hash_set::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 element at the indicated position and returns a node handle |
| // owning that extracted data. |
| // |
| // node_type extract(const key_type& x): |
| // |
| // Extracts the element with the key matching the passed key value and |
| // returns a node handle owning that extracted data. If the `flat_hash_set` |
| // does not contain an element with a matching key, this function returns an |
| // empty node handle. |
| using Base::extract; |
| |
| // flat_hash_set::merge() |
| // |
| // Extracts elements from a given `source` flat hash set into this |
| // `flat_hash_set`. If the destination `flat_hash_set` already contains an |
| // element with an equivalent key, that element is not extracted. |
| using Base::merge; |
| |
| // flat_hash_set::swap(flat_hash_set& other) |
| // |
| // Exchanges the contents of this `flat_hash_set` with those of the `other` |
| // flat hash set, avoiding invocation of any move, copy, or swap operations on |
| // individual elements. |
| // |
| // All iterators and references on the `flat_hash_set` remain valid, excepting |
| // for the past-the-end iterator, which is invalidated. |
| // |
| // `swap()` requires that the flat hash set's hashing and key equivalence |
| // functions be Swappable, and are exchaged using unqualified calls to |
| // non-member `swap()`. If the set'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_set::rehash(count) |
| // |
| // Rehashes the `flat_hash_set`, 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_set`, references are also |
| // invalidated upon a `rehash()`. |
| using Base::rehash; |
| |
| // flat_hash_set::reserve(count) |
| // |
| // Sets the number of slots in the `flat_hash_set` 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_set::contains() |
| // |
| // Determines whether an element comparing equal to the given `key` exists |
| // within the `flat_hash_set`, returning `true` if so or `false` otherwise. |
| using Base::contains; |
| |
| // flat_hash_set::count(const Key& key) const |
| // |
| // Returns the number of elements comparing equal to the given `key` within |
| // the `flat_hash_set`. note that this function will return either `1` or `0` |
| // since duplicate elements are not allowed within a `flat_hash_set`. |
| using Base::count; |
| |
| // flat_hash_set::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_set`. |
| using Base::equal_range; |
| |
| // flat_hash_set::find() |
| // |
| // Finds an element with the passed `key` within the `flat_hash_set`. |
| using Base::find; |
| |
| // flat_hash_set::bucket_count() |
| // |
| // Returns the number of "buckets" within the `flat_hash_set`. Note that |
| // because a flat hash set contains all elements within its internal storage, |
| // this value simply equals the current capacity of the `flat_hash_set`. |
| using Base::bucket_count; |
| |
| // flat_hash_set::load_factor() |
| // |
| // Returns the current load factor of the `flat_hash_set` (the average number |
| // of slots occupied with a value within the hash set). |
| using Base::load_factor; |
| |
| // flat_hash_set::max_load_factor() |
| // |
| // Manages the maximum load factor of the `flat_hash_set`. Overloads are |
| // listed below. |
| // |
| // float flat_hash_set::max_load_factor() |
| // |
| // Returns the current maximum load factor of the `flat_hash_set`. |
| // |
| // void flat_hash_set::max_load_factor(float ml) |
| // |
| // Sets the maximum load factor of the `flat_hash_set` to the passed value. |
| // |
| // NOTE: This overload is provided only for API compatibility with the STL; |
| // `flat_hash_set` will ignore any set load factor and manage its rehashing |
| // internally as an implementation detail. |
| using Base::max_load_factor; |
| |
| // flat_hash_set::get_allocator() |
| // |
| // Returns the allocator function associated with this `flat_hash_set`. |
| using Base::get_allocator; |
| |
| // flat_hash_set::hash_function() |
| // |
| // Returns the hashing function used to hash the keys within this |
| // `flat_hash_set`. |
| using Base::hash_function; |
| |
| // flat_hash_set::key_eq() |
| // |
| // Returns the function used for comparing keys equality. |
| using Base::key_eq; |
| }; |
| |
| // erase_if(flat_hash_set<>, Pred) |
| // |
| // Erases all elements that satisfy the predicate `pred` from the container `c`. |
| // Returns the number of erased elements. |
| template <typename T, typename H, typename E, typename A, typename Predicate> |
| typename flat_hash_set<T, H, E, A>::size_type erase_if( |
| flat_hash_set<T, H, E, A>& c, Predicate pred) { |
| return container_internal::EraseIf(pred, &c); |
| } |
| |
| namespace container_internal { |
| |
| template <class T> |
| struct FlatHashSetPolicy { |
| using slot_type = T; |
| using key_type = T; |
| using init_type = T; |
| using constant_iterators = std::true_type; |
| |
| template <class Allocator, class... Args> |
| static void construct(Allocator* alloc, slot_type* slot, Args&&... args) { |
| absl::allocator_traits<Allocator>::construct(*alloc, slot, |
| std::forward<Args>(args)...); |
| } |
| |
| template <class Allocator> |
| static void destroy(Allocator* alloc, slot_type* slot) { |
| absl::allocator_traits<Allocator>::destroy(*alloc, slot); |
| } |
| |
| template <class Allocator> |
| static void transfer(Allocator* alloc, slot_type* new_slot, |
| slot_type* old_slot) { |
| construct(alloc, new_slot, std::move(*old_slot)); |
| destroy(alloc, old_slot); |
| } |
| |
| static T& element(slot_type* slot) { return *slot; } |
| |
| template <class F, class... Args> |
| static decltype(absl::container_internal::DecomposeValue( |
| std::declval<F>(), std::declval<Args>()...)) |
| apply(F&& f, Args&&... args) { |
| return absl::container_internal::DecomposeValue( |
| std::forward<F>(f), std::forward<Args>(args)...); |
| } |
| |
| static size_t space_used(const T*) { return 0; } |
| }; |
| } // namespace container_internal |
| |
| namespace container_algorithm_internal { |
| |
| // Specialization of trait in absl/algorithm/container.h |
| template <class Key, class Hash, class KeyEqual, class Allocator> |
| struct IsUnorderedContainer<absl::flat_hash_set<Key, Hash, KeyEqual, Allocator>> |
| : std::true_type {}; |
| |
| } // namespace container_algorithm_internal |
| |
| ABSL_NAMESPACE_END |
| } // namespace absl |
| |
| #endif // ABSL_CONTAINER_FLAT_HASH_SET_H_ |