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authorGravatar Abseil Team <absl-team@google.com>2018-09-27 12:24:54 -0700
committerGravatar Derek Mauro <dmauro@google.com>2018-09-27 15:28:12 -0400
commit48cd2c3f351ff188bc85684b84a91b6e6d17d896 (patch)
tree6f92b0cbb0f8282b7df1cd567cb66406fbbb6f80 /absl/container/flat_hash_set.h
parente291c279e458761e77a69b09b129d3d1e81f1e80 (diff)
Export of internal Abseil changes.
-- 4eacae3ff1b14b1d309e8092185bc10e8a6203cf by Derek Mauro <dmauro@google.com>: Release SwissTable - a fast, efficient, cache-friendly hash table. https://www.youtube.com/watch?v=ncHmEUmJZf4 PiperOrigin-RevId: 214816527 -- df8c3dfab3cfb2f4365909a84d0683b193cfbb11 by Derek Mauro <dmauro@google.com>: Internal change PiperOrigin-RevId: 214785288 -- 1eabd5266bbcebc33eecc91e5309b751856a75c8 by Abseil Team <absl-team@google.com>: Internal change PiperOrigin-RevId: 214722931 -- 2ebbfac950f83146b46253038e7dd7dcde9f2951 by Derek Mauro <dmauro@google.com>: Internal change PiperOrigin-RevId: 214701684 GitOrigin-RevId: 4eacae3ff1b14b1d309e8092185bc10e8a6203cf Change-Id: I9ba64e395b22ad7863213d157b8019b082adc19d
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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: 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/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 {
+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()`, `operator[]()` 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_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_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:
+ 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_map` 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: 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_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. 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_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. 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_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 map 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 map, 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 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_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 map 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 map).
+ 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;
+};
+
+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 absl
+#endif // ABSL_CONTAINER_FLAT_HASH_SET_H_