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+// 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: node_hash_set.h
+// -----------------------------------------------------------------------------
+//
+// An `absl::node_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 map elements can be done
+// as an `O(1)` operation. However, `node_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 table should be a map of type
+// `flat_hash_map` or a set of type `flat_hash_set`. However, if you need
+// pointer stability, a `node_hash_set` should be your preferred choice. As
+// well, if you are migrating your code from using `std::unordered_set`, a
+// `node_hash_set` should be an easy migration. Consider migrating to
+// `node_hash_set` and perhaps converting to a more efficient `flat_hash_set`
+// upon further review.
+
+#ifndef ABSL_CONTAINER_NODE_HASH_SET_H_
+#define ABSL_CONTAINER_NODE_HASH_SET_H_
+
+#include <type_traits>
+
+#include "absl/algorithm/container.h"
+#include "absl/container/internal/hash_function_defaults.h" // IWYU pragma: export
+#include "absl/container/internal/node_hash_policy.h"
+#include "absl/container/internal/raw_hash_set.h" // IWYU pragma: export
+#include "absl/memory/memory.h"
+
+namespace absl {
+inline namespace lts_2018_12_18 {
+namespace container_internal {
+template <typename T>
+struct NodeHashSetPolicy;
+} // namespace container_internal
+
+// -----------------------------------------------------------------------------
+// absl::node_hash_set
+// -----------------------------------------------------------------------------
+//
+// An `absl::node_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:
+//
+// * 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 set.
+// * Returns `void` from the `erase(iterator)` overload.
+//
+// By default, `node_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 `node_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.
+//
+// Example:
+//
+// // Create a node hash set of three strings
+// absl::node_hash_map<std::string, std::string> ducks =
+// {"huey", "dewey"}, "louie"};
+//
+// // Insert a new element into the node hash map
+// ducks.insert("donald"};
+//
+// // Force a rehash of the node hash map
+// 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 Alloc = std::allocator<T>>
+class node_hash_set
+ : public absl::container_internal::raw_hash_set<
+ absl::container_internal::NodeHashSetPolicy<T>, Hash, Eq, Alloc> {
+ using Base = typename node_hash_set::raw_hash_set;
+
+ public:
+ // Constructors and Assignment Operators
+ //
+ // A node_hash_set 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_set<std::string> set1;
+ //
+ // * Initializer List constructor
+ //
+ // absl::node_hash_set<std::string> set2 =
+ // {{"huey"}, {"dewey"}, {"louie"},};
+ //
+ // * Copy constructor
+ //
+ // absl::node_hash_set<std::string> set3(set2);
+ //
+ // * Copy assignment operator
+ //
+ // // Hash functor and Comparator are copied as well
+ // absl::node_hash_set<std::string> set4;
+ // set4 = set3;
+ //
+ // * Move constructor
+ //
+ // // Move is guaranteed efficient
+ // absl::node_hash_set<std::string> set5(std::move(set4));
+ //
+ // * Move assignment operator
+ //
+ // // May be efficient if allocators are compatible
+ // absl::node_hash_set<std::string> set6;
+ // set6 = std::move(set5);
+ //
+ // * Range constructor
+ //
+ // std::vector<std::string> v = {"a", "b"};
+ // absl::node_hash_set<std::string> set7(v.begin(), v.end());
+ node_hash_set() {}
+ using Base::Base;
+
+ // node_hash_set::begin()
+ //
+ // Returns an iterator to the beginning of the `node_hash_set`.
+ using Base::begin;
+
+ // node_hash_set::cbegin()
+ //
+ // Returns a const iterator to the beginning of the `node_hash_set`.
+ using Base::cbegin;
+
+ // node_hash_set::cend()
+ //
+ // Returns a const iterator to the end of the `node_hash_set`.
+ using Base::cend;
+
+ // node_hash_set::end()
+ //
+ // Returns an iterator to the end of the `node_hash_set`.
+ using Base::end;
+
+ // node_hash_set::capacity()
+ //
+ // Returns the number of element slots (assigned, deleted, and empty)
+ // available within the `node_hash_set`.
+ //
+ // NOTE: this member function is particular to `absl::node_hash_set` and is
+ // not provided in the `std::unordered_map` API.
+ using Base::capacity;
+
+ // node_hash_set::empty()
+ //
+ // Returns whether or not the `node_hash_set` is empty.
+ using Base::empty;
+
+ // node_hash_set::max_size()
+ //
+ // Returns the largest theoretical possible number of elements within a
+ // `node_hash_set` under current memory constraints. This value can be thought
+ // of the largest value of `std::distance(begin(), end())` for a
+ // `node_hash_set<T>`.
+ using Base::max_size;
+
+ // node_hash_set::size()
+ //
+ // Returns the number of elements currently within the `node_hash_set`.
+ using Base::size;
+
+ // node_hash_set::clear()
+ //
+ // Removes all elements from the `node_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;
+
+ // node_hash_set::erase()
+ //
+ // Erases elements within the `node_hash_set`. Erasing does not trigger a
+ // rehash. Overloads are listed below.
+ //
+ // void erase(const_iterator pos):
+ //
+ // Erases the element at `position` of the `node_hash_set`, 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;
+
+ // node_hash_set::insert()
+ //
+ // Inserts an element of the specified value into the `node_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 `node_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 `node_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 `node_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
+ // `node_hash_set` we guarantee the first match is inserted.
+ using Base::insert;
+
+ // node_hash_set::emplace()
+ //
+ // Inserts an element of the specified value by constructing it in-place
+ // within the `node_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;
+
+ // node_hash_set::emplace_hint()
+ //
+ // Inserts an element of the specified value by constructing it in-place
+ // within the `node_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;
+
+ // node_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 `node_hash_set`
+ // does not contain an element with a matching key, this function returns an
+ // empty node handle.
+ using Base::extract;
+
+ // node_hash_set::merge()
+ //
+ // Extracts elements from a given `source` flat hash map into this
+ // `node_hash_set`. If the destination `node_hash_set` already contains an
+ // element with an equivalent key, that element is not extracted.
+ using Base::merge;
+
+ // node_hash_set::swap(node_hash_set& other)
+ //
+ // Exchanges the contents of this `node_hash_set` 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 `node_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 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_set::rehash(count)
+ //
+ // Rehashes the `node_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;
+
+ // node_hash_set::reserve(count)
+ //
+ // Sets the number of slots in the `node_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;
+
+ // node_hash_set::contains()
+ //
+ // Determines whether an element comparing equal to the given `key` exists
+ // within the `node_hash_set`, returning `true` if so or `false` otherwise.
+ using Base::contains;
+
+ // node_hash_set::count(const Key& key) const
+ //
+ // Returns the number of elements comparing equal to the given `key` within
+ // the `node_hash_set`. note that this function will return either `1` or `0`
+ // since duplicate elements are not allowed within a `node_hash_set`.
+ using Base::count;
+
+ // node_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
+ // `node_hash_set`.
+ using Base::equal_range;
+
+ // node_hash_set::find()
+ //
+ // Finds an element with the passed `key` within the `node_hash_set`.
+ using Base::find;
+
+ // node_hash_set::bucket_count()
+ //
+ // Returns the number of "buckets" within the `node_hash_set`. Note that
+ // because a flat hash map contains all elements within its internal storage,
+ // this value simply equals the current capacity of the `node_hash_set`.
+ using Base::bucket_count;
+
+ // node_hash_set::load_factor()
+ //
+ // Returns the current load factor of the `node_hash_set` (the average number
+ // of slots occupied with a value within the hash map).
+ using Base::load_factor;
+
+ // node_hash_set::max_load_factor()
+ //
+ // Manages the maximum load factor of the `node_hash_set`. Overloads are
+ // listed below.
+ //
+ // float node_hash_set::max_load_factor()
+ //
+ // Returns the current maximum load factor of the `node_hash_set`.
+ //
+ // void node_hash_set::max_load_factor(float ml)
+ //
+ // Sets the maximum load factor of the `node_hash_set` to the passed value.
+ //
+ // NOTE: This overload is provided only for API compatibility with the STL;
+ // `node_hash_set` will ignore any set load factor and manage its rehashing
+ // internally as an implementation detail.
+ using Base::max_load_factor;
+
+ // node_hash_set::get_allocator()
+ //
+ // Returns the allocator function associated with this `node_hash_set`.
+ using Base::get_allocator;
+
+ // node_hash_set::hash_function()
+ //
+ // Returns the hashing function used to hash the keys within this
+ // `node_hash_set`.
+ using Base::hash_function;
+
+ // node_hash_set::key_eq()
+ //
+ // Returns the function used for comparing keys equality.
+ using Base::key_eq;
+
+ ABSL_DEPRECATED("Call `hash_function()` instead.")
+ typename Base::hasher hash_funct() { return this->hash_function(); }
+
+ ABSL_DEPRECATED("Call `rehash()` instead.")
+ void resize(typename Base::size_type hint) { this->rehash(hint); }
+};
+
+namespace container_internal {
+
+template <class T>
+struct NodeHashSetPolicy
+ : absl::container_internal::node_hash_policy<T&, NodeHashSetPolicy<T>> {
+ using key_type = T;
+ using init_type = T;
+ using constant_iterators = std::true_type;
+
+ template <class Allocator, class... Args>
+ static T* new_element(Allocator* alloc, Args&&... args) {
+ using ValueAlloc =
+ typename absl::allocator_traits<Allocator>::template rebind_alloc<T>;
+ ValueAlloc value_alloc(*alloc);
+ T* res = absl::allocator_traits<ValueAlloc>::allocate(value_alloc, 1);
+ absl::allocator_traits<ValueAlloc>::construct(value_alloc, res,
+ std::forward<Args>(args)...);
+ return res;
+ }
+
+ template <class Allocator>
+ static void delete_element(Allocator* alloc, T* elem) {
+ using ValueAlloc =
+ typename absl::allocator_traits<Allocator>::template rebind_alloc<T>;
+ ValueAlloc value_alloc(*alloc);
+ absl::allocator_traits<ValueAlloc>::destroy(value_alloc, elem);
+ absl::allocator_traits<ValueAlloc>::deallocate(value_alloc, elem, 1);
+ }
+
+ 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 element_space_used(const T*) { return sizeof(T); }
+};
+} // 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::node_hash_set<Key, Hash, KeyEqual, Allocator>>
+ : std::true_type {};
+
+} // namespace container_algorithm_internal
+} // inline namespace lts_2018_12_18
+} // namespace absl
+
+#endif // ABSL_CONTAINER_NODE_HASH_SET_H_