504 lines
18 KiB
C
504 lines
18 KiB
C
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// Copyright 2018 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// File: flat_hash_set.h
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// -----------------------------------------------------------------------------
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//
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// An `absl::flat_hash_set<T>` is an unordered associative container designed to
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// be a more efficient replacement for `std::unordered_set`. Like
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// `unordered_set`, search, insertion, and deletion of set elements can be done
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// as an `O(1)` operation. However, `flat_hash_set` (and other unordered
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// associative containers known as the collection of Abseil "Swiss tables")
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// contain other optimizations that result in both memory and computation
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// advantages.
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//
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// In most cases, your default choice for a hash set should be a set of type
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// `flat_hash_set`.
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#ifndef ABSL_CONTAINER_FLAT_HASH_SET_H_
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#define ABSL_CONTAINER_FLAT_HASH_SET_H_
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#include <type_traits>
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#include <utility>
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#include "absl/algorithm/container.h"
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#include "absl/base/macros.h"
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#include "absl/container/internal/container_memory.h"
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#include "absl/container/internal/hash_function_defaults.h" // IWYU pragma: export
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#include "absl/container/internal/raw_hash_set.h" // IWYU pragma: export
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#include "absl/memory/memory.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace container_internal {
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template <typename T>
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struct FlatHashSetPolicy;
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} // namespace container_internal
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// -----------------------------------------------------------------------------
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// absl::flat_hash_set
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// -----------------------------------------------------------------------------
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//
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// An `absl::flat_hash_set<T>` is an unordered associative container which has
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// been optimized for both speed and memory footprint in most common use cases.
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// Its interface is similar to that of `std::unordered_set<T>` with the
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// following notable differences:
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//
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// * Requires keys that are CopyConstructible
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// * Supports heterogeneous lookup, through `find()` and `insert()`, provided
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// that the set is provided a compatible heterogeneous hashing function and
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// equality operator.
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// * Invalidates any references and pointers to elements within the table after
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// `rehash()`.
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// * Contains a `capacity()` member function indicating the number of element
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// slots (open, deleted, and empty) within the hash set.
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// * Returns `void` from the `erase(iterator)` overload.
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//
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// By default, `flat_hash_set` uses the `absl::Hash` hashing framework. All
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// fundamental and Abseil types that support the `absl::Hash` framework have a
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// compatible equality operator for comparing insertions into `flat_hash_map`.
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// If your type is not yet supported by the `absl::Hash` framework, see
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// absl/hash/hash.h for information on extending Abseil hashing to user-defined
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// types.
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//
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// NOTE: A `flat_hash_set` stores its keys directly inside its implementation
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// array to avoid memory indirection. Because a `flat_hash_set` is designed to
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// move data when rehashed, set keys will not retain pointer stability. If you
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// require pointer stability, consider using
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// `absl::flat_hash_set<std::unique_ptr<T>>`. If your type is not moveable and
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// you require pointer stability, consider `absl::node_hash_set` instead.
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//
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// Example:
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//
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// // Create a flat hash set of three strings
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// absl::flat_hash_set<std::string> ducks =
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// {"huey", "dewey", "louie"};
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//
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// // Insert a new element into the flat hash set
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// ducks.insert("donald");
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//
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// // Force a rehash of the flat hash set
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// ducks.rehash(0);
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//
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// // See if "dewey" is present
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// if (ducks.contains("dewey")) {
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// std::cout << "We found dewey!" << std::endl;
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// }
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template <class T, class Hash = absl::container_internal::hash_default_hash<T>,
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class Eq = absl::container_internal::hash_default_eq<T>,
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class Allocator = std::allocator<T>>
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class flat_hash_set
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: public absl::container_internal::raw_hash_set<
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absl::container_internal::FlatHashSetPolicy<T>, Hash, Eq, Allocator> {
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using Base = typename flat_hash_set::raw_hash_set;
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public:
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// Constructors and Assignment Operators
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//
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// A flat_hash_set supports the same overload set as `std::unordered_map`
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// for construction and assignment:
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//
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// * Default constructor
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//
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// // No allocation for the table's elements is made.
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// absl::flat_hash_set<std::string> set1;
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//
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// * Initializer List constructor
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//
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// absl::flat_hash_set<std::string> set2 =
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// {{"huey"}, {"dewey"}, {"louie"},};
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//
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// * Copy constructor
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//
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// absl::flat_hash_set<std::string> set3(set2);
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//
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// * Copy assignment operator
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//
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// // Hash functor and Comparator are copied as well
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// absl::flat_hash_set<std::string> set4;
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// set4 = set3;
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//
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// * Move constructor
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//
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// // Move is guaranteed efficient
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// absl::flat_hash_set<std::string> set5(std::move(set4));
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//
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// * Move assignment operator
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//
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// // May be efficient if allocators are compatible
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// absl::flat_hash_set<std::string> set6;
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// set6 = std::move(set5);
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//
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// * Range constructor
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//
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// std::vector<std::string> v = {"a", "b"};
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// absl::flat_hash_set<std::string> set7(v.begin(), v.end());
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flat_hash_set() {}
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using Base::Base;
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// flat_hash_set::begin()
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//
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// Returns an iterator to the beginning of the `flat_hash_set`.
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using Base::begin;
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// flat_hash_set::cbegin()
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//
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// Returns a const iterator to the beginning of the `flat_hash_set`.
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using Base::cbegin;
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// flat_hash_set::cend()
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//
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// Returns a const iterator to the end of the `flat_hash_set`.
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using Base::cend;
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// flat_hash_set::end()
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//
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// Returns an iterator to the end of the `flat_hash_set`.
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using Base::end;
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// flat_hash_set::capacity()
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//
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// Returns the number of element slots (assigned, deleted, and empty)
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// available within the `flat_hash_set`.
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//
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// NOTE: this member function is particular to `absl::flat_hash_set` and is
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// not provided in the `std::unordered_map` API.
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using Base::capacity;
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// flat_hash_set::empty()
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//
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// Returns whether or not the `flat_hash_set` is empty.
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using Base::empty;
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// flat_hash_set::max_size()
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//
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// Returns the largest theoretical possible number of elements within a
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// `flat_hash_set` under current memory constraints. This value can be thought
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// of the largest value of `std::distance(begin(), end())` for a
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// `flat_hash_set<T>`.
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using Base::max_size;
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// flat_hash_set::size()
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//
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// Returns the number of elements currently within the `flat_hash_set`.
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using Base::size;
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// flat_hash_set::clear()
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//
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// Removes all elements from the `flat_hash_set`. Invalidates any references,
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// pointers, or iterators referring to contained elements.
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//
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// NOTE: this operation may shrink the underlying buffer. To avoid shrinking
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// the underlying buffer call `erase(begin(), end())`.
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using Base::clear;
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// flat_hash_set::erase()
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//
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// Erases elements within the `flat_hash_set`. Erasing does not trigger a
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// rehash. Overloads are listed below.
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//
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// void erase(const_iterator pos):
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//
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// Erases the element at `position` of the `flat_hash_set`, returning
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// `void`.
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//
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// NOTE: returning `void` in this case is different than that of STL
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// containers in general and `std::unordered_set` in particular (which
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// return an iterator to the element following the erased element). If that
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// iterator is needed, simply post increment the iterator:
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//
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// set.erase(it++);
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//
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// iterator erase(const_iterator first, const_iterator last):
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//
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// Erases the elements in the open interval [`first`, `last`), returning an
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// iterator pointing to `last`.
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//
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// size_type erase(const key_type& key):
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//
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// Erases the element with the matching key, if it exists.
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using Base::erase;
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// flat_hash_set::insert()
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//
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// Inserts an element of the specified value into the `flat_hash_set`,
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// returning an iterator pointing to the newly inserted element, provided that
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// an element with the given key does not already exist. If rehashing occurs
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// due to the insertion, all iterators are invalidated. Overloads are listed
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// below.
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//
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// std::pair<iterator,bool> insert(const T& value):
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//
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// Inserts a value into the `flat_hash_set`. Returns a pair consisting of an
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// iterator to the inserted element (or to the element that prevented the
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// insertion) and a bool denoting whether the insertion took place.
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//
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// std::pair<iterator,bool> insert(T&& value):
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//
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// Inserts a moveable value into the `flat_hash_set`. Returns a pair
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// consisting of an iterator to the inserted element (or to the element that
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// prevented the insertion) and a bool denoting whether the insertion took
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// place.
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//
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// iterator insert(const_iterator hint, const T& value):
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// iterator insert(const_iterator hint, T&& value):
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//
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// Inserts a value, using the position of `hint` as a non-binding suggestion
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// for where to begin the insertion search. Returns an iterator to the
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// inserted element, or to the existing element that prevented the
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// insertion.
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//
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// void insert(InputIterator first, InputIterator last):
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//
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// Inserts a range of values [`first`, `last`).
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//
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// NOTE: Although the STL does not specify which element may be inserted if
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// multiple keys compare equivalently, for `flat_hash_set` we guarantee the
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// first match is inserted.
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//
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// void insert(std::initializer_list<T> ilist):
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//
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// Inserts the elements within the initializer list `ilist`.
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//
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// NOTE: Although the STL does not specify which element may be inserted if
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// multiple keys compare equivalently within the initializer list, for
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// `flat_hash_set` we guarantee the first match is inserted.
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using Base::insert;
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// flat_hash_set::emplace()
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//
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// Inserts an element of the specified value by constructing it in-place
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// within the `flat_hash_set`, provided that no element with the given key
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// already exists.
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//
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// The element may be constructed even if there already is an element with the
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// key in the container, in which case the newly constructed element will be
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// destroyed immediately.
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//
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// If rehashing occurs due to the insertion, all iterators are invalidated.
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using Base::emplace;
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// flat_hash_set::emplace_hint()
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//
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// Inserts an element of the specified value by constructing it in-place
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// within the `flat_hash_set`, using the position of `hint` as a non-binding
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// suggestion for where to begin the insertion search, and only inserts
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// provided that no element with the given key already exists.
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//
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// The element may be constructed even if there already is an element with the
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// key in the container, in which case the newly constructed element will be
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// destroyed immediately.
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//
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// If rehashing occurs due to the insertion, all iterators are invalidated.
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using Base::emplace_hint;
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// flat_hash_set::extract()
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//
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// Extracts the indicated element, erasing it in the process, and returns it
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// as a C++17-compatible node handle. Overloads are listed below.
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//
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// node_type extract(const_iterator position):
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//
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// Extracts the element at the indicated position and returns a node handle
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// owning that extracted data.
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//
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// node_type extract(const key_type& x):
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//
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// Extracts the element with the key matching the passed key value and
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// returns a node handle owning that extracted data. If the `flat_hash_set`
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// does not contain an element with a matching key, this function returns an
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// empty node handle.
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using Base::extract;
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// flat_hash_set::merge()
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//
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// Extracts elements from a given `source` flat hash map into this
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// `flat_hash_set`. If the destination `flat_hash_set` already contains an
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// element with an equivalent key, that element is not extracted.
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using Base::merge;
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// flat_hash_set::swap(flat_hash_set& other)
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//
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// Exchanges the contents of this `flat_hash_set` with those of the `other`
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// flat hash map, avoiding invocation of any move, copy, or swap operations on
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// individual elements.
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//
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// All iterators and references on the `flat_hash_set` remain valid, excepting
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// for the past-the-end iterator, which is invalidated.
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//
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// `swap()` requires that the flat hash set's hashing and key equivalence
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// functions be Swappable, and are exchaged using unqualified calls to
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// non-member `swap()`. If the map's allocator has
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// `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
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// set to `true`, the allocators are also exchanged using an unqualified call
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// to non-member `swap()`; otherwise, the allocators are not swapped.
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using Base::swap;
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// flat_hash_set::rehash(count)
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//
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// Rehashes the `flat_hash_set`, setting the number of slots to be at least
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// the passed value. If the new number of slots increases the load factor more
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// than the current maximum load factor
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// (`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;
|
||
|
|
};
|
||
|
|
|
||
|
|
// erase_if(flat_hash_set<>, Pred)
|
||
|
|
//
|
||
|
|
// Erases all elements that satisfy the predicate `pred` from the container `c`.
|
||
|
|
template <typename T, typename H, typename E, typename A, typename Predicate>
|
||
|
|
void erase_if(flat_hash_set<T, H, E, A>& c, Predicate pred) {
|
||
|
|
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);
|
||
|
|
}
|
||
|
|
|
||
|
|
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
|
||
|
|
|
||
|
|
ABSL_NAMESPACE_END
|
||
|
|
} // namespace absl
|
||
|
|
|
||
|
|
#endif // ABSL_CONTAINER_FLAT_HASH_SET_H_
|