flat_hash_set.h - mozsearch

// 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`. The special case of calling

  //   `erase(begin(), end())` resets the reserved growth such that if

  //   `reserve(N)` has previously been called and there has been no intervening

  //   call to `clear()`, then after calling `erase(begin(), end())`, it is safe

  //   to assume that inserting N elements will not cause a rehash.

//

  // 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 exchanged 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);

  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_

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