absl/container/node_hash_set.h - master - jiteman/jsd-fork-abseil-cpp

absl/container/node_hash_set.h
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04 апр 2025, 21:47
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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
//
//      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: 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 set 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.
//
// 'node_hash_set' is not exception-safe.

#ifndef ABSL_CONTAINER_NODE_HASH_SET_H_
#define ABSL_CONTAINER_NODE_HASH_SET_H_

#include <cstddef>
#include <memory>
#include <type_traits>

#include "absl/algorithm/container.h"
#include "absl/base/attributes.h"
#include "absl/container/hash_container_defaults.h"
#include "absl/container/internal/container_memory.h"
#include "absl/container/internal/node_slot_policy.h"
#include "absl/container/internal/raw_hash_set.h"  // IWYU pragma: export
#include "absl/memory/memory.h"
#include "absl/meta/type_traits.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
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 set is provided a compatible heterogeneous
//   hashing function and equality operator. See below for details.
// * 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.
//
// Using 'absl::node_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.
//
// To achieve heterogeneous lookup for custom types either 'Hash' and 'Eq' type
// parameters can be used or 'T' should have public inner types
// 'absl_container_hash' and (optionally) 'absl_container_eq'. In either case,
// 'typename Hash::is_transparent' and 'typename Eq::is_transparent' should be
// well-formed. Both types are basically functors:
// * 'Hash' should support 'size_t operator()(U val) const' that returns a hash
// for the given 'val'.
// * 'Eq' should support 'bool operator()(U lhs, V rhs) const' that returns true
// if 'lhs' is equal to 'rhs'.
//
// In most cases 'T' needs only to provide the 'absl_container_hash'. In this
// case 'std::equal_to<void>' will be used instead of 'eq' part.
//
// PERFORMANCE WARNING: Erasure & sparsity can negatively affect performance:
//  * Iteration takes O(capacity) time, not O(size).
//  * erase() slows down begin() and ++iterator.
//  * Capacity only shrinks on rehash() or clear() -- not on erase().
//
// Example:
//
//   // Create a node hash set of three strings
//   absl::node_hash_set<std::string> ducks =
//     {"huey", "dewey", "louie"};
//
//  // Insert a new element into the node hash set
//  ducks.insert("donald");
//
//  // Force a rehash of the node 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 = DefaultHashContainerHash<T>,
          class Eq = DefaultHashContainerEq<T>, class Alloc = std::allocator<T>>
class ABSL_ATTRIBUTE_OWNER 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_set'
  // 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_set' 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: Returning 'void' in this case is different than that of STL
  //   containers in general and 'std::unordered_map' in particular (which
  //   return an iterator to the element following the erased element). If that
  //   iterator is needed, simply post increment the iterator:
  //
  //     map.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;

  // 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' node hash set 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'
  // node hash set.
  //
  // 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 node 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;

  // 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 node hash set 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 set).
  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;
};

// erase_if(node_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 node_hash_set<T, H, E, A>::size_type erase_if(
    node_hash_set<T, H, E, A>& c, Predicate pred) {
  return container_internal::EraseIf(pred, &c);
}

// swap(node_hash_set<>, node_hash_set<>)
//
// Swaps the contents of two 'node_hash_set' containers.
//
// NOTE: we need to define this function template in order for
// 'flat_hash_set::swap' to be called instead of 'std::swap'. Even though we
// have 'swap(raw_hash_set&, raw_hash_set&)' defined, that function requires a
// derived-to-base conversion, whereas 'std::swap' is a function template so
// 'std::swap' will be preferred by compiler.
template <typename T, typename H, typename E, typename A>
void swap(node_hash_set<T, H, E, A>& x,
          node_hash_set<T, H, E, A>& y) noexcept(noexcept(x.swap(y))) {
  return x.swap(y);
}

namespace container_internal {

// c_for_each_fast(node_hash_set<>, Function)
//
// Container-based version of the <algorithm> 'std::for_each()' function to
// apply a function to a container's elements.
// There is no guarantees on the order of the function calls.
// Erasure and/or insertion of elements in the function is not allowed.
template <typename T, typename H, typename E, typename A, typename Function>
decay_t<Function> c_for_each_fast(const node_hash_set<T, H, E, A>& c,
                                  Function&& f) {
  container_internal::ForEach(f, &c);
  return f;
}
template <typename T, typename H, typename E, typename A, typename Function>
decay_t<Function> c_for_each_fast(node_hash_set<T, H, E, A>& c, Function&& f) {
  container_internal::ForEach(f, &c);
  return f;
}
template <typename T, typename H, typename E, typename A, typename Function>
decay_t<Function> c_for_each_fast(node_hash_set<T, H, E, A>&& c, Function&& f) {
  container_internal::ForEach(f, &c);
  return f;
}

}  // namespace container_internal

namespace container_internal {

template <class T>
struct NodeHashSetPolicy
    : absl::container_internal::node_slot_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); }

  template <class Hash>
  static constexpr HashSlotFn get_hash_slot_fn() {
    return &TypeErasedDerefAndApplyToSlotFn<Hash, 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
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CONTAINER_NODE_HASH_SET_H_