610 lines
23 KiB
C++
610 lines
23 KiB
C++
// 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_map.h
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// -----------------------------------------------------------------------------
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//
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// An `absl::flat_hash_map<K, V>` is an unordered associative container of
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// unique keys and associated values designed to be a more efficient replacement
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// for `std::unordered_map`. Like `unordered_map`, search, insertion, and
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// deletion of map elements can be done as an `O(1)` operation. However,
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// `flat_hash_map` (and other unordered associative containers known as the
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// collection of Abseil "Swiss tables") contain other optimizations that result
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// in both memory and computation advantages.
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//
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// In most cases, your default choice for a hash map should be a map of type
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// `flat_hash_map`.
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#ifndef ABSL_CONTAINER_FLAT_HASH_MAP_H_
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#define ABSL_CONTAINER_FLAT_HASH_MAP_H_
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#include <cstddef>
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#include <new>
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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_map.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 <class K, class V>
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struct FlatHashMapPolicy;
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} // namespace container_internal
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// -----------------------------------------------------------------------------
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// absl::flat_hash_map
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// -----------------------------------------------------------------------------
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//
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// An `absl::flat_hash_map<K, V>` is an unordered associative container which
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// has been optimized for both speed and memory footprint in most common use
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// cases. Its interface is similar to that of `std::unordered_map<K, V>` with
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// the following notable differences:
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//
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// * Requires keys that are CopyConstructible
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// * Requires values that are MoveConstructible
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// * Supports heterogeneous lookup, through `find()`, `operator[]()` and
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// `insert()`, provided that the map is provided a compatible heterogeneous
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// hashing function and 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 map.
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// * Returns `void` from the `erase(iterator)` overload.
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//
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// By default, `flat_hash_map` uses the `absl::Hash` hashing framework.
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// All fundamental and Abseil types that support the `absl::Hash` framework have
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// a 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_map` stores its value types directly inside its
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// implementation array to avoid memory indirection. Because a `flat_hash_map`
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// is designed to move data when rehashed, map values will not retain pointer
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// stability. If you require pointer stability, or if your values are large,
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// consider using `absl::flat_hash_map<Key, std::unique_ptr<Value>>` instead.
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// If your types are not moveable or you require pointer stability for keys,
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// consider `absl::node_hash_map`.
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//
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// Example:
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//
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// // Create a flat hash map of three strings (that map to strings)
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// absl::flat_hash_map<std::string, std::string> ducks =
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// {{"a", "huey"}, {"b", "dewey"}, {"c", "louie"}};
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//
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// // Insert a new element into the flat hash map
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// ducks.insert({"d", "donald"});
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//
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// // Force a rehash of the flat hash map
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// ducks.rehash(0);
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//
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// // Find the element with the key "b"
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// std::string search_key = "b";
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// auto result = ducks.find(search_key);
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// if (result != ducks.end()) {
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// std::cout << "Result: " << result->second << std::endl;
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// }
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template <class K, class V,
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class Hash = absl::container_internal::hash_default_hash<K>,
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class Eq = absl::container_internal::hash_default_eq<K>,
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class Allocator = std::allocator<std::pair<const K, V>>>
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class flat_hash_map : public absl::container_internal::raw_hash_map<
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absl::container_internal::FlatHashMapPolicy<K, V>,
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Hash, Eq, Allocator> {
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using Base = typename flat_hash_map::raw_hash_map;
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public:
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// Constructors and Assignment Operators
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//
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// A flat_hash_map 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_map<int, std::string> map1;
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//
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// * Initializer List constructor
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//
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// absl::flat_hash_map<int, std::string> map2 =
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// {{1, "huey"}, {2, "dewey"}, {3, "louie"},};
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//
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// * Copy constructor
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//
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// absl::flat_hash_map<int, std::string> map3(map2);
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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_map<int, std::string> map4;
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// map4 = map3;
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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_map<int, std::string> map5(std::move(map4));
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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_map<int, std::string> map6;
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// map6 = std::move(map5);
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//
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// * Range constructor
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//
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// std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};
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// absl::flat_hash_map<int, std::string> map7(v.begin(), v.end());
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flat_hash_map() {}
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using Base::Base;
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// flat_hash_map::begin()
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//
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// Returns an iterator to the beginning of the `flat_hash_map`.
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using Base::begin;
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// flat_hash_map::cbegin()
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//
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// Returns a const iterator to the beginning of the `flat_hash_map`.
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using Base::cbegin;
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// flat_hash_map::cend()
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//
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// Returns a const iterator to the end of the `flat_hash_map`.
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using Base::cend;
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// flat_hash_map::end()
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//
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// Returns an iterator to the end of the `flat_hash_map`.
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using Base::end;
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// flat_hash_map::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_map`.
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//
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// NOTE: this member function is particular to `absl::flat_hash_map` 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_map::empty()
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//
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// Returns whether or not the `flat_hash_map` is empty.
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using Base::empty;
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// flat_hash_map::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_map` 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_map<K, V>`.
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using Base::max_size;
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// flat_hash_map::size()
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//
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// Returns the number of elements currently within the `flat_hash_map`.
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using Base::size;
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// flat_hash_map::clear()
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//
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// Removes all elements from the `flat_hash_map`. 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_map::erase()
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//
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// Erases elements within the `flat_hash_map`. 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_map`, 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_map` 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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// map.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_map::insert()
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//
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// Inserts an element of the specified value into the `flat_hash_map`,
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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 init_type& value):
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//
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// Inserts a value into the `flat_hash_map`. 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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// std::pair<iterator,bool> insert(init_type&& value):
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//
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// Inserts a moveable value into the `flat_hash_map`. 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 init_type& value):
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// iterator insert(const_iterator hint, T&& value):
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// iterator insert(const_iterator hint, init_type&& 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_map` we guarantee the
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// first match is inserted.
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//
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// void insert(std::initializer_list<init_type> 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_map` we guarantee the first match is inserted.
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using Base::insert;
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// flat_hash_map::insert_or_assign()
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//
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// Inserts an element of the specified value into the `flat_hash_map` provided
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// that a value with the given key does not already exist, or replaces it with
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// the element value if a key for that value already exists, returning an
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// iterator pointing to the newly inserted element. If rehashing occurs due
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// to the insertion, all existing iterators are invalidated. Overloads are
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// listed below.
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//
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// pair<iterator, bool> insert_or_assign(const init_type& k, T&& obj):
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// pair<iterator, bool> insert_or_assign(init_type&& k, T&& obj):
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//
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// Inserts/Assigns (or moves) the element of the specified key into the
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// `flat_hash_map`.
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//
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// iterator insert_or_assign(const_iterator hint,
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// const init_type& k, T&& obj):
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// iterator insert_or_assign(const_iterator hint, init_type&& k, T&& obj):
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//
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// Inserts/Assigns (or moves) the element of the specified key into the
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// `flat_hash_map` using the position of `hint` as a non-binding suggestion
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// for where to begin the insertion search.
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using Base::insert_or_assign;
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// flat_hash_map::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_map`, 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. Prefer `try_emplace()` unless your key is not
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// copyable or moveable.
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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_map::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_map`, 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. Prefer `try_emplace()` unless your key is not
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// copyable or moveable.
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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_map::try_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_map`, provided that no element with the given key
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// already exists. Unlike `emplace()`, if an element with the given key
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// already exists, we guarantee that no element is constructed.
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//
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// If rehashing occurs due to the insertion, all iterators are invalidated.
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// Overloads are listed below.
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//
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// pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):
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// pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):
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//
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// Inserts (via copy or move) the element of the specified key into the
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// `flat_hash_map`.
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//
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// iterator try_emplace(const_iterator hint,
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// const init_type& k, Args&&... args):
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// iterator try_emplace(const_iterator hint, init_type&& k, Args&&... args):
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//
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// Inserts (via copy or move) the element of the specified key into the
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// `flat_hash_map` using the position of `hint` as a non-binding suggestion
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// for where to begin the insertion search.
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//
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// All `try_emplace()` overloads make the same guarantees regarding rvalue
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// arguments as `std::unordered_map::try_emplace()`, namely that these
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// functions will not move from rvalue arguments if insertions do not happen.
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using Base::try_emplace;
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// flat_hash_map::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 key,value pair of the element at the indicated position and
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// returns a node handle 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 key,value pair of the element with a key matching the passed
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// key value and returns a node handle owning that extracted data. If the
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// `flat_hash_map` does not contain an element with a matching key, this
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// function returns an empty node handle.
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//
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// NOTE: when compiled in an earlier version of C++ than C++17,
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// `node_type::key()` returns a const reference to the key instead of a
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// mutable reference. We cannot safely return a mutable reference without
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// std::launder (which is not available before C++17).
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using Base::extract;
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// flat_hash_map::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_map`. If the destination `flat_hash_map` 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_map::swap(flat_hash_map& other)
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//
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// Exchanges the contents of this `flat_hash_map` 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_map` 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 map's hashing and key equivalence
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// functions be Swappable, and are exchanged 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_map::rehash(count)
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//
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// Rehashes the `flat_hash_map`, 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_map`, references are also
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// invalidated upon a `rehash()`.
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using Base::rehash;
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// flat_hash_map::reserve(count)
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//
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// Sets the number of slots in the `flat_hash_map` 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_map::at()
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//
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// Returns a reference to the mapped value of the element with key equivalent
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// to the passed key.
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using Base::at;
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// flat_hash_map::contains()
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//
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// Determines whether an element with a key comparing equal to the given `key`
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// exists within the `flat_hash_map`, returning `true` if so or `false`
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// otherwise.
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using Base::contains;
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// flat_hash_map::count(const Key& key) const
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//
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// Returns the number of elements with a key comparing equal to the given
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// `key` within the `flat_hash_map`. note that this function will return
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// either `1` or `0` since duplicate keys are not allowed within a
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// `flat_hash_map`.
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using Base::count;
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// flat_hash_map::equal_range()
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//
|
|
// 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_map`.
|
|
using Base::equal_range;
|
|
|
|
// flat_hash_map::find()
|
|
//
|
|
// Finds an element with the passed `key` within the `flat_hash_map`.
|
|
using Base::find;
|
|
|
|
// flat_hash_map::operator[]()
|
|
//
|
|
// Returns a reference to the value mapped to the passed key within the
|
|
// `flat_hash_map`, performing an `insert()` if the key does not already
|
|
// exist.
|
|
//
|
|
// If an insertion occurs and results in a rehashing of the container, all
|
|
// iterators are invalidated. Otherwise iterators are not affected and
|
|
// references are not invalidated. Overloads are listed below.
|
|
//
|
|
// T& operator[](const Key& key):
|
|
//
|
|
// Inserts an init_type object constructed in-place if the element with the
|
|
// given key does not exist.
|
|
//
|
|
// T& operator[](Key&& key):
|
|
//
|
|
// Inserts an init_type object constructed in-place provided that an element
|
|
// with the given key does not exist.
|
|
using Base::operator[];
|
|
|
|
// flat_hash_map::bucket_count()
|
|
//
|
|
// Returns the number of "buckets" within the `flat_hash_map`. 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_map`.
|
|
using Base::bucket_count;
|
|
|
|
// flat_hash_map::load_factor()
|
|
//
|
|
// Returns the current load factor of the `flat_hash_map` (the average number
|
|
// of slots occupied with a value within the hash map).
|
|
using Base::load_factor;
|
|
|
|
// flat_hash_map::max_load_factor()
|
|
//
|
|
// Manages the maximum load factor of the `flat_hash_map`. Overloads are
|
|
// listed below.
|
|
//
|
|
// float flat_hash_map::max_load_factor()
|
|
//
|
|
// Returns the current maximum load factor of the `flat_hash_map`.
|
|
//
|
|
// void flat_hash_map::max_load_factor(float ml)
|
|
//
|
|
// Sets the maximum load factor of the `flat_hash_map` to the passed value.
|
|
//
|
|
// NOTE: This overload is provided only for API compatibility with the STL;
|
|
// `flat_hash_map` will ignore any set load factor and manage its rehashing
|
|
// internally as an implementation detail.
|
|
using Base::max_load_factor;
|
|
|
|
// flat_hash_map::get_allocator()
|
|
//
|
|
// Returns the allocator function associated with this `flat_hash_map`.
|
|
using Base::get_allocator;
|
|
|
|
// flat_hash_map::hash_function()
|
|
//
|
|
// Returns the hashing function used to hash the keys within this
|
|
// `flat_hash_map`.
|
|
using Base::hash_function;
|
|
|
|
// flat_hash_map::key_eq()
|
|
//
|
|
// Returns the function used for comparing keys equality.
|
|
using Base::key_eq;
|
|
};
|
|
|
|
// erase_if(flat_hash_map<>, Pred)
|
|
//
|
|
// Erases all elements that satisfy the predicate `pred` from the container `c`.
|
|
// Returns the number of erased elements.
|
|
template <typename K, typename V, typename H, typename E, typename A,
|
|
typename Predicate>
|
|
typename flat_hash_map<K, V, H, E, A>::size_type erase_if(
|
|
flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
|
|
return container_internal::EraseIf(pred, &c);
|
|
}
|
|
|
|
namespace container_internal {
|
|
|
|
template <class K, class V>
|
|
struct FlatHashMapPolicy {
|
|
using slot_policy = container_internal::map_slot_policy<K, V>;
|
|
using slot_type = typename slot_policy::slot_type;
|
|
using key_type = K;
|
|
using mapped_type = V;
|
|
using init_type = std::pair</*non const*/ key_type, mapped_type>;
|
|
|
|
template <class Allocator, class... Args>
|
|
static void construct(Allocator* alloc, slot_type* slot, Args&&... args) {
|
|
slot_policy::construct(alloc, slot, std::forward<Args>(args)...);
|
|
}
|
|
|
|
template <class Allocator>
|
|
static void destroy(Allocator* alloc, slot_type* slot) {
|
|
slot_policy::destroy(alloc, slot);
|
|
}
|
|
|
|
template <class Allocator>
|
|
static void transfer(Allocator* alloc, slot_type* new_slot,
|
|
slot_type* old_slot) {
|
|
slot_policy::transfer(alloc, new_slot, old_slot);
|
|
}
|
|
|
|
template <class F, class... Args>
|
|
static decltype(absl::container_internal::DecomposePair(
|
|
std::declval<F>(), std::declval<Args>()...))
|
|
apply(F&& f, Args&&... args) {
|
|
return absl::container_internal::DecomposePair(std::forward<F>(f),
|
|
std::forward<Args>(args)...);
|
|
}
|
|
|
|
static size_t space_used(const slot_type*) { return 0; }
|
|
|
|
static std::pair<const K, V>& element(slot_type* slot) { return slot->value; }
|
|
|
|
static V& value(std::pair<const K, V>* kv) { return kv->second; }
|
|
static const V& value(const std::pair<const K, V>* kv) { return kv->second; }
|
|
};
|
|
|
|
} // namespace container_internal
|
|
|
|
namespace container_algorithm_internal {
|
|
|
|
// Specialization of trait in absl/algorithm/container.h
|
|
template <class Key, class T, class Hash, class KeyEqual, class Allocator>
|
|
struct IsUnorderedContainer<
|
|
absl::flat_hash_map<Key, T, Hash, KeyEqual, Allocator>> : std::true_type {};
|
|
|
|
} // namespace container_algorithm_internal
|
|
|
|
ABSL_NAMESPACE_END
|
|
} // namespace absl
|
|
|
|
#endif // ABSL_CONTAINER_FLAT_HASH_MAP_H_
|