// 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 {
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_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.
//
// 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_map`
// 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_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: 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.
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 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 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
} // namespace absl
#endif // ABSL_CONTAINER_FLAT_HASH_SET_H_
