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506 lines
18 KiB
506 lines
18 KiB
// 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, returning the |
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// number of elements erased (0 or 1). |
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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 set 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 |
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// will be at least `size()` / `max_load_factor()`. |
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// |
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// To force a rehash, pass rehash(0). |
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// |
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// NOTE: unlike behavior in `std::unordered_set`, references are also |
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// invalidated upon a `rehash()`. |
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using Base::rehash; |
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// flat_hash_set::reserve(count) |
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// |
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// Sets the number of slots in the `flat_hash_set` to the number needed to |
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// accommodate at least `count` total elements without exceeding the current |
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// maximum load factor, and may rehash the container if needed. |
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using Base::reserve; |
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// flat_hash_set::contains() |
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// |
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// Determines whether an element comparing equal to the given `key` exists |
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// within the `flat_hash_set`, returning `true` if so or `false` otherwise. |
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using Base::contains; |
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// flat_hash_set::count(const Key& key) const |
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// |
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// Returns the number of elements comparing equal to the given `key` within |
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// the `flat_hash_set`. note that this function will return either `1` or `0` |
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// since duplicate elements are not allowed within a `flat_hash_set`. |
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using Base::count; |
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// flat_hash_set::equal_range() |
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// |
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// Returns a closed range [first, last], defined by a `std::pair` of two |
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// iterators, containing all elements with the passed key in the |
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// `flat_hash_set`. |
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using Base::equal_range; |
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// flat_hash_set::find() |
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// |
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// Finds an element with the passed `key` within the `flat_hash_set`. |
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using Base::find; |
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// flat_hash_set::bucket_count() |
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// |
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// Returns the number of "buckets" within the `flat_hash_set`. Note that |
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// because a flat hash map contains all elements within its internal storage, |
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// this value simply equals the current capacity of the `flat_hash_set`. |
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using Base::bucket_count; |
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// flat_hash_set::load_factor() |
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// |
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// Returns the current load factor of the `flat_hash_set` (the average number |
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// of slots occupied with a value within the hash map). |
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using Base::load_factor; |
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// flat_hash_set::max_load_factor() |
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// |
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// Manages the maximum load factor of the `flat_hash_set`. Overloads are |
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// listed below. |
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// |
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// float flat_hash_set::max_load_factor() |
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// |
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// Returns the current maximum load factor of the `flat_hash_set`. |
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// |
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// void flat_hash_set::max_load_factor(float ml) |
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// |
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// Sets the maximum load factor of the `flat_hash_set` to the passed value. |
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// |
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// NOTE: This overload is provided only for API compatibility with the STL; |
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// `flat_hash_set` will ignore any set load factor and manage its rehashing |
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// internally as an implementation detail. |
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using Base::max_load_factor; |
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// flat_hash_set::get_allocator() |
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// |
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// Returns the allocator function associated with this `flat_hash_set`. |
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using Base::get_allocator; |
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// flat_hash_set::hash_function() |
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// |
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// Returns the hashing function used to hash the keys within this |
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// `flat_hash_set`. |
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using Base::hash_function; |
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// flat_hash_set::key_eq() |
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// |
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// Returns the function used for comparing keys equality. |
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using Base::key_eq; |
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}; |
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// erase_if(flat_hash_set<>, Pred) |
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// |
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// Erases all elements that satisfy the predicate `pred` from the container `c`. |
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// Returns the number of erased elements. |
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template <typename T, typename H, typename E, typename A, typename Predicate> |
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typename flat_hash_set<T, H, E, A>::size_type erase_if( |
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flat_hash_set<T, H, E, A>& c, Predicate pred) { |
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return container_internal::EraseIf(pred, &c); |
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} |
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namespace container_internal { |
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template <class T> |
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struct FlatHashSetPolicy { |
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using slot_type = T; |
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using key_type = T; |
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using init_type = T; |
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using constant_iterators = std::true_type; |
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template <class Allocator, class... Args> |
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static void construct(Allocator* alloc, slot_type* slot, Args&&... args) { |
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absl::allocator_traits<Allocator>::construct(*alloc, slot, |
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std::forward<Args>(args)...); |
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} |
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template <class Allocator> |
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static void destroy(Allocator* alloc, slot_type* slot) { |
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absl::allocator_traits<Allocator>::destroy(*alloc, slot); |
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} |
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template <class Allocator> |
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static void transfer(Allocator* alloc, slot_type* new_slot, |
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slot_type* old_slot) { |
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construct(alloc, new_slot, std::move(*old_slot)); |
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destroy(alloc, old_slot); |
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} |
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static T& element(slot_type* slot) { return *slot; } |
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template <class F, class... Args> |
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static decltype(absl::container_internal::DecomposeValue( |
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std::declval<F>(), std::declval<Args>()...)) |
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apply(F&& f, Args&&... args) { |
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return absl::container_internal::DecomposeValue( |
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std::forward<F>(f), std::forward<Args>(args)...); |
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} |
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static size_t space_used(const T*) { return 0; } |
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}; |
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} // namespace container_internal |
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namespace container_algorithm_internal { |
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// Specialization of trait in absl/algorithm/container.h |
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template <class Key, class Hash, class KeyEqual, class Allocator> |
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struct IsUnorderedContainer<absl::flat_hash_set<Key, Hash, KeyEqual, Allocator>> |
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: std::true_type {}; |
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} // namespace container_algorithm_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#endif // ABSL_CONTAINER_FLAT_HASH_SET_H_
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