// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// -----------------------------------------------------------------------------
// File: flat_hash_map.h
// -----------------------------------------------------------------------------
//
// An `absl::flat_hash_map<K, V>` is an unordered associative container of
// unique keys and associated values designed to be a more efficient replacement
// for `std::unordered_map`. Like `unordered_map`, search, insertion, and
// deletion of map elements can be done as an `O(1)` operation. However,
// `flat_hash_map` (and other unordered associative containers known as the
// collection of Abseil "Swiss tables") contain other optimizations that result
// in both memory and computation advantages.
//
// In most cases, your default choice for a hash map should be a map of type
// `flat_hash_map`.
#ifndef ABSL_CONTAINER_FLAT_HASH_MAP_H_
#define ABSL_CONTAINER_FLAT_HASH_MAP_H_
#include <cstddef>
#include <new>
#include <type_traits>
#include <utility>
#include "absl/algorithm/container.h"
#include "absl/container/internal/container_memory.h"
#include "absl/container/internal/hash_function_defaults.h" // IWYU pragma: export
#include "absl/container/internal/raw_hash_map.h" // IWYU pragma: export
#include "absl/memory/memory.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {
template <class K, class V>
struct FlatHashMapPolicy;
} // namespace container_internal
// -----------------------------------------------------------------------------
// absl::flat_hash_map
// -----------------------------------------------------------------------------
//
// An `absl::flat_hash_map<K, V>` is an unordered associative container which
// has been optimized for both speed and memory footprint in most common use
// cases. Its interface is similar to that of `std::unordered_map<K, V>` with
// the following notable differences:
//
// * Requires keys that are CopyConstructible
// * Requires values that are MoveConstructible
// * Supports heterogeneous lookup, through `find()`, `operator[]()` and
// `insert()`, provided that the map is provided a compatible heterogeneous
// hashing function and equality operator.
// * Invalidates any references and pointers to elements within the table after
// `rehash()`.
// * Contains a `capacity()` member function indicating the number of element
// slots (open, deleted, and empty) within the hash map.
// * Returns `void` from the `erase(iterator)` overload.
//
// By default, `flat_hash_map` uses the `absl::Hash` hashing framework.
// All fundamental and Abseil types that support the `absl::Hash` framework have
// a compatible equality operator for comparing insertions into `flat_hash_map`.
// If your type is not yet supported by the `absl::Hash` framework, see
// absl/hash/hash.h for information on extending Abseil hashing to user-defined
// types.
//
// NOTE: A `flat_hash_map` stores its value types directly inside its
// implementation array to avoid memory indirection. Because a `flat_hash_map`
// is designed to move data when rehashed, map values will not retain pointer
// stability. If you require pointer stability, or if your values are large,
// consider using `absl::flat_hash_map<Key, std::unique_ptr<Value>>` instead.
// If your types are not moveable or you require pointer stability for keys,
// consider `absl::node_hash_map`.
//
// Example:
//
// // Create a flat hash map of three strings (that map to strings)
// absl::flat_hash_map<std::string, std::string> ducks =
// {{"a", "huey"}, {"b", "dewey"}, {"c", "louie"}};
//
// // Insert a new element into the flat hash map
// ducks.insert({"d", "donald"});
//
// // Force a rehash of the flat hash map
// ducks.rehash(0);
//
// // Find the element with the key "b"
// std::string search_key = "b";
// auto result = ducks.find(search_key);
// if (result != ducks.end()) {
// std::cout << "Result: " << result->second << std::endl;
// }
template <class K, class V,
class Hash = absl::container_internal::hash_default_hash<K>,
class Eq = absl::container_internal::hash_default_eq<K>,
class Allocator = std::allocator<std::pair<const K, V>>>
class flat_hash_map : public absl::container_internal::raw_hash_map<
absl::container_internal::FlatHashMapPolicy<K, V>,
Hash, Eq, Allocator> {
using Base = typename flat_hash_map::raw_hash_map;
public:
// Constructors and Assignment Operators
//
// A flat_hash_map supports the same overload set as `std::unordered_map`
// for construction and assignment:
//
// * Default constructor
//
// // No allocation for the table's elements is made.
// absl::flat_hash_map<int, std::string> map1;
//
// * Initializer List constructor
//
// absl::flat_hash_map<int, std::string> map2 =
// {{1, "huey"}, {2, "dewey"}, {3, "louie"},};
//
// * Copy constructor
//
// absl::flat_hash_map<int, std::string> map3(map2);
//
// * Copy assignment operator
//
// // Hash functor and Comparator are copied as well
// absl::flat_hash_map<int, std::string> map4;
// map4 = map3;
//
// * Move constructor
//
// // Move is guaranteed efficient
// absl::flat_hash_map<int, std::string> map5(std::move(map4));
//
// * Move assignment operator
//
// // May be efficient if allocators are compatible
// absl::flat_hash_map<int, std::string> map6;
// map6 = std::move(map5);
//
// * Range constructor
//
// std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};
// absl::flat_hash_map<int, std::string> map7(v.begin(), v.end());
flat_hash_map() {}
using Base::Base;
// flat_hash_map::begin()
//
// Returns an iterator to the beginning of the `flat_hash_map`.
using Base::begin;
// flat_hash_map::cbegin()
//
// Returns a const iterator to the beginning of the `flat_hash_map`.
using Base::cbegin;
// flat_hash_map::cend()
//
// Returns a const iterator to the end of the `flat_hash_map`.
using Base::cend;
// flat_hash_map::end()
//
// Returns an iterator to the end of the `flat_hash_map`.
using Base::end;
// flat_hash_map::capacity()
//
// Returns the number of element slots (assigned, deleted, and empty)
// available within the `flat_hash_map`.
//
// NOTE: this member function is particular to `absl::flat_hash_map` and is
// not provided in the `std::unordered_map` API.
using Base::capacity;
// flat_hash_map::empty()
//
// Returns whether or not the `flat_hash_map` is empty.
using Base::empty;
// flat_hash_map::max_size()
//
// Returns the largest theoretical possible number of elements within a
// `flat_hash_map` under current memory constraints. This value can be thought
// of the largest value of `std::distance(begin(), end())` for a
// `flat_hash_map<K, V>`.
using Base::max_size;
// flat_hash_map::size()
//
// Returns the number of elements currently within the `flat_hash_map`.
using Base::size;
// flat_hash_map::clear()
//
// Removes all elements from the `flat_hash_map`. Invalidates any references,
// pointers, or iterators referring to contained elements.
//
// NOTE: this operation may shrink the underlying buffer. To avoid shrinking
// the underlying buffer call `erase(begin(), end())`.
using Base::clear;
// flat_hash_map::erase()
//
// Erases elements within the `flat_hash_map`. Erasing does not trigger a
// rehash. Overloads are listed below.
//
// void erase(const_iterator pos):
//
// Erases the element at `position` of the `flat_hash_map`, returning
// `void`.
//
// NOTE: returning `void` in this case is different than that of STL
// containers in general and `std::unordered_map` in particular (which
// return an iterator to the element following the erased element). If that
// iterator is needed, simply post increment the iterator:
//
// map.erase(it++);
//
// iterator erase(const_iterator first, const_iterator last):
//
// Erases the elements in the open interval [`first`, `last`), returning an
// iterator pointing to `last`.
//
// size_type erase(const key_type& key):
//
// Erases the element with the matching key, if it exists, returning the
// number of elements erased (0 or 1).
using Base::erase;
// flat_hash_map::insert()
//
// Inserts an element of the specified value into the `flat_hash_map`,
// returning an iterator pointing to the newly inserted element, provided that
// an element with the given key does not already exist. If rehashing occurs
// due to the insertion, all iterators are invalidated. Overloads are listed
// below.
//
// std::pair<iterator,bool> insert(const init_type& value):
//
// Inserts a value into the `flat_hash_map`. Returns a pair consisting of an
// iterator to the inserted element (or to the element that prevented the
// insertion) and a bool denoting whether the insertion took place.
//
// std::pair<iterator,bool> insert(T&& value):
// std::pair<iterator,bool> insert(init_type&& value):
//
// Inserts a moveable value into the `flat_hash_map`. Returns a pair
// consisting of an iterator to the inserted element (or to the element that
// prevented the insertion) and a bool denoting whether the insertion took
// place.
//
// iterator insert(const_iterator hint, const init_type& value):
// iterator insert(const_iterator hint, T&& value):
// iterator insert(const_iterator hint, init_type&& value);
//
// Inserts a value, using the position of `hint` as a non-binding suggestion
// for where to begin the insertion search. Returns an iterator to the
// inserted element, or to the existing element that prevented the
// insertion.
//
// void insert(InputIterator first, InputIterator last):
//
// Inserts a range of values [`first`, `last`).
//
// NOTE: Although the STL does not specify which element may be inserted if
// multiple keys compare equivalently, for `flat_hash_map` we guarantee the
// first match is inserted.
//
// void insert(std::initializer_list<init_type> ilist):
//
// Inserts the elements within the initializer list `ilist`.
//
// NOTE: Although the STL does not specify which element may be inserted if
// multiple keys compare equivalently within the initializer list, for
// `flat_hash_map` we guarantee the first match is inserted.
using Base::insert;
// flat_hash_map::insert_or_assign()
//
// Inserts an element of the specified value into the `flat_hash_map` provided
// that a value with the given key does not already exist, or replaces it with
// the element value if a key for that value already exists, returning an
// iterator pointing to the newly inserted element. If rehashing occurs due
// to the insertion, all existing iterators are invalidated. Overloads are
// listed below.
//
// pair<iterator, bool> insert_or_assign(const init_type& k, T&& obj):
// pair<iterator, bool> insert_or_assign(init_type&& k, T&& obj):
//
// Inserts/Assigns (or moves) the element of the specified key into the
// `flat_hash_map`.
//
// iterator insert_or_assign(const_iterator hint,
// const init_type& k, T&& obj):
// iterator insert_or_assign(const_iterator hint, init_type&& k, T&& obj):
//
// Inserts/Assigns (or moves) the element of the specified key into the
// `flat_hash_map` using the position of `hint` as a non-binding suggestion
// for where to begin the insertion search.
using Base::insert_or_assign;
// flat_hash_map::emplace()
//
// Inserts an element of the specified value by constructing it in-place
// within the `flat_hash_map`, provided that no element with the given key
// already exists.
//
// The element may be constructed even if there already is an element with the
// key in the container, in which case the newly constructed element will be
// destroyed immediately. Prefer `try_emplace()` unless your key is not
// copyable or moveable.
//
// If rehashing occurs due to the insertion, all iterators are invalidated.
using Base::emplace;
// flat_hash_map::emplace_hint()
//
// Inserts an element of the specified value by constructing it in-place
// within the `flat_hash_map`, using the position of `hint` as a non-binding
// suggestion for where to begin the insertion search, and only inserts
// provided that no element with the given key already exists.
//
// The element may be constructed even if there already is an element with the
// key in the container, in which case the newly constructed element will be
// destroyed immediately. Prefer `try_emplace()` unless your key is not
// copyable or moveable.
//
// If rehashing occurs due to the insertion, all iterators are invalidated.
using Base::emplace_hint;
// flat_hash_map::try_emplace()
//
// Inserts an element of the specified value by constructing it in-place
// within the `flat_hash_map`, provided that no element with the given key
// already exists. Unlike `emplace()`, if an element with the given key
// already exists, we guarantee that no element is constructed.
//
// If rehashing occurs due to the insertion, all iterators are invalidated.
// Overloads are listed below.
//
// pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):
// pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):
//
// Inserts (via copy or move) the element of the specified key into the
// `flat_hash_map`.
//
// iterator try_emplace(const_iterator hint,
// const init_type& k, Args&&... args):
// iterator try_emplace(const_iterator hint, init_type&& k, Args&&... args):
//
// Inserts (via copy or move) the element of the specified key into the
// `flat_hash_map` using the position of `hint` as a non-binding suggestion
// for where to begin the insertion search.
//
// All `try_emplace()` overloads make the same guarantees regarding rvalue
// arguments as `std::unordered_map::try_emplace()`, namely that these
// functions will not move from rvalue arguments if insertions do not happen.
using Base::try_emplace;
// flat_hash_map::extract()
//
// Extracts the indicated element, erasing it in the process, and returns it
// as a C++17-compatible node handle. Overloads are listed below.
//
// node_type extract(const_iterator position):
//
// Extracts the key,value pair of the element at the indicated position and
// returns a node handle owning that extracted data.
//
// node_type extract(const key_type& x):
//
// Extracts the key,value pair of the element with a key matching the passed
// key value and returns a node handle owning that extracted data. If the
// `flat_hash_map` does not contain an element with a matching key, this
// function returns an empty node handle.
//
// NOTE: when compiled in an earlier version of C++ than C++17,
// `node_type::key()` returns a const reference to the key instead of a
// mutable reference. We cannot safely return a mutable reference without
// std::launder (which is not available before C++17).
using Base::extract;
// flat_hash_map::merge()
//
// Extracts elements from a given `source` flat hash map into this
// `flat_hash_map`. If the destination `flat_hash_map` already contains an
// element with an equivalent key, that element is not extracted.
using Base::merge;
// flat_hash_map::swap(flat_hash_map& other)
//
// Exchanges the contents of this `flat_hash_map` with those of the `other`
// flat hash map, avoiding invocation of any move, copy, or swap operations on
// individual elements.
//
// All iterators and references on the `flat_hash_map` remain valid, excepting
// for the past-the-end iterator, which is invalidated.
//
// `swap()` requires that the flat hash map's hashing and key equivalence
// functions be Swappable, and are exchanged using unqualified calls to
// non-member `swap()`. If the map's allocator has
// `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
// set to `true`, the allocators are also exchanged using an unqualified call
// to non-member `swap()`; otherwise, the allocators are not swapped.
using Base::swap;
// flat_hash_map::rehash(count)
//
// Rehashes the `flat_hash_map`, setting the number of slots to be at least
// the passed value. If the new number of slots increases the load factor more
// than the current maximum load factor
// (`count` < `size()` / `max_load_factor()`), then the new number of slots
// will be at least `size()` / `max_load_factor()`.
//
// To force a rehash, pass rehash(0).
//
// NOTE: unlike behavior in `std::unordered_map`, references are also
// invalidated upon a `rehash()`.
using Base::rehash;
// flat_hash_map::reserve(count)
//
// Sets the number of slots in the `flat_hash_map` 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_map::at()
//
// Returns a reference to the mapped value of the element with key equivalent
// to the passed key.
using Base::at;
// flat_hash_map::contains()
//
// Determines whether an element with a key comparing equal to the given `key`
// exists within the `flat_hash_map`, returning `true` if so or `false`
// otherwise.
using Base::contains;
// flat_hash_map::count(const Key& key) const
//
// Returns the number of elements with a key comparing equal to the given
// `key` within the `flat_hash_map`. note that this function will return
// either `1` or `0` since duplicate keys are not allowed within a
// `flat_hash_map`.
using Base::count;
// flat_hash_map::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_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`.
template <typename K, typename V, typename H, typename E, typename A,
typename Predicate>
void erase_if(flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
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_
