Back to home page

EIC code displayed by LXR

 
 

    


File indexing completed on 2025-01-18 09:27:15

0001 // Copyright 2018 The Abseil Authors.
0002 //
0003 // Licensed under the Apache License, Version 2.0 (the "License");
0004 // you may not use this file except in compliance with the License.
0005 // You may obtain a copy of the License at
0006 //
0007 //      https://www.apache.org/licenses/LICENSE-2.0
0008 //
0009 // Unless required by applicable law or agreed to in writing, software
0010 // distributed under the License is distributed on an "AS IS" BASIS,
0011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
0012 // See the License for the specific language governing permissions and
0013 // limitations under the License.
0014 //
0015 // -----------------------------------------------------------------------------
0016 // File: flat_hash_map.h
0017 // -----------------------------------------------------------------------------
0018 //
0019 // An `absl::flat_hash_map<K, V>` is an unordered associative container of
0020 // unique keys and associated values designed to be a more efficient replacement
0021 // for `std::unordered_map`. Like `unordered_map`, search, insertion, and
0022 // deletion of map elements can be done as an `O(1)` operation. However,
0023 // `flat_hash_map` (and other unordered associative containers known as the
0024 // collection of Abseil "Swiss tables") contain other optimizations that result
0025 // in both memory and computation advantages.
0026 //
0027 // In most cases, your default choice for a hash map should be a map of type
0028 // `flat_hash_map`.
0029 //
0030 // `flat_hash_map` is not exception-safe.
0031 
0032 #ifndef ABSL_CONTAINER_FLAT_HASH_MAP_H_
0033 #define ABSL_CONTAINER_FLAT_HASH_MAP_H_
0034 
0035 #include <cstddef>
0036 #include <memory>
0037 #include <type_traits>
0038 #include <utility>
0039 
0040 #include "absl/algorithm/container.h"
0041 #include "absl/base/attributes.h"
0042 #include "absl/base/macros.h"
0043 #include "absl/container/hash_container_defaults.h"
0044 #include "absl/container/internal/container_memory.h"
0045 #include "absl/container/internal/raw_hash_map.h"  // IWYU pragma: export
0046 #include "absl/meta/type_traits.h"
0047 
0048 namespace absl {
0049 ABSL_NAMESPACE_BEGIN
0050 namespace container_internal {
0051 template <class K, class V>
0052 struct FlatHashMapPolicy;
0053 }  // namespace container_internal
0054 
0055 // -----------------------------------------------------------------------------
0056 // absl::flat_hash_map
0057 // -----------------------------------------------------------------------------
0058 //
0059 // An `absl::flat_hash_map<K, V>` is an unordered associative container which
0060 // has been optimized for both speed and memory footprint in most common use
0061 // cases. Its interface is similar to that of `std::unordered_map<K, V>` with
0062 // the following notable differences:
0063 //
0064 // * Requires keys that are CopyConstructible
0065 // * Requires values that are MoveConstructible
0066 // * Supports heterogeneous lookup, through `find()`, `operator[]()` and
0067 //   `insert()`, provided that the map is provided a compatible heterogeneous
0068 //   hashing function and equality operator. See below for details.
0069 // * Invalidates any references and pointers to elements within the table after
0070 //   `rehash()` and when the table is moved.
0071 // * Contains a `capacity()` member function indicating the number of element
0072 //   slots (open, deleted, and empty) within the hash map.
0073 // * Returns `void` from the `erase(iterator)` overload.
0074 //
0075 // By default, `flat_hash_map` uses the `absl::Hash` hashing framework.
0076 // All fundamental and Abseil types that support the `absl::Hash` framework have
0077 // a compatible equality operator for comparing insertions into `flat_hash_map`.
0078 // If your type is not yet supported by the `absl::Hash` framework, see
0079 // absl/hash/hash.h for information on extending Abseil hashing to user-defined
0080 // types.
0081 //
0082 // Using `absl::flat_hash_map` at interface boundaries in dynamically loaded
0083 // libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may
0084 // be randomized across dynamically loaded libraries.
0085 //
0086 // To achieve heterogeneous lookup for custom types either `Hash` and `Eq` type
0087 // parameters can be used or `T` should have public inner types
0088 // `absl_container_hash` and (optionally) `absl_container_eq`. In either case,
0089 // `typename Hash::is_transparent` and `typename Eq::is_transparent` should be
0090 // well-formed. Both types are basically functors:
0091 // * `Hash` should support `size_t operator()(U val) const` that returns a hash
0092 // for the given `val`.
0093 // * `Eq` should support `bool operator()(U lhs, V rhs) const` that returns true
0094 // if `lhs` is equal to `rhs`.
0095 //
0096 // In most cases `T` needs only to provide the `absl_container_hash`. In this
0097 // case `std::equal_to<void>` will be used instead of `eq` part.
0098 //
0099 // NOTE: A `flat_hash_map` stores its value types directly inside its
0100 // implementation array to avoid memory indirection. Because a `flat_hash_map`
0101 // is designed to move data when rehashed, map values will not retain pointer
0102 // stability. If you require pointer stability, or if your values are large,
0103 // consider using `absl::flat_hash_map<Key, std::unique_ptr<Value>>` instead.
0104 // If your types are not moveable or you require pointer stability for keys,
0105 // consider `absl::node_hash_map`.
0106 //
0107 // Example:
0108 //
0109 //   // Create a flat hash map of three strings (that map to strings)
0110 //   absl::flat_hash_map<std::string, std::string> ducks =
0111 //     {{"a", "huey"}, {"b", "dewey"}, {"c", "louie"}};
0112 //
0113 //  // Insert a new element into the flat hash map
0114 //  ducks.insert({"d", "donald"});
0115 //
0116 //  // Force a rehash of the flat hash map
0117 //  ducks.rehash(0);
0118 //
0119 //  // Find the element with the key "b"
0120 //  std::string search_key = "b";
0121 //  auto result = ducks.find(search_key);
0122 //  if (result != ducks.end()) {
0123 //    std::cout << "Result: " << result->second << std::endl;
0124 //  }
0125 template <class K, class V, class Hash = DefaultHashContainerHash<K>,
0126           class Eq = DefaultHashContainerEq<K>,
0127           class Allocator = std::allocator<std::pair<const K, V>>>
0128 class ABSL_INTERNAL_ATTRIBUTE_OWNER flat_hash_map
0129     : public absl::container_internal::raw_hash_map<
0130           absl::container_internal::FlatHashMapPolicy<K, V>, Hash, Eq,
0131           Allocator> {
0132   using Base = typename flat_hash_map::raw_hash_map;
0133 
0134  public:
0135   // Constructors and Assignment Operators
0136   //
0137   // A flat_hash_map supports the same overload set as `std::unordered_map`
0138   // for construction and assignment:
0139   //
0140   // *  Default constructor
0141   //
0142   //    // No allocation for the table's elements is made.
0143   //    absl::flat_hash_map<int, std::string> map1;
0144   //
0145   // * Initializer List constructor
0146   //
0147   //   absl::flat_hash_map<int, std::string> map2 =
0148   //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};
0149   //
0150   // * Copy constructor
0151   //
0152   //   absl::flat_hash_map<int, std::string> map3(map2);
0153   //
0154   // * Copy assignment operator
0155   //
0156   //  // Hash functor and Comparator are copied as well
0157   //  absl::flat_hash_map<int, std::string> map4;
0158   //  map4 = map3;
0159   //
0160   // * Move constructor
0161   //
0162   //   // Move is guaranteed efficient
0163   //   absl::flat_hash_map<int, std::string> map5(std::move(map4));
0164   //
0165   // * Move assignment operator
0166   //
0167   //   // May be efficient if allocators are compatible
0168   //   absl::flat_hash_map<int, std::string> map6;
0169   //   map6 = std::move(map5);
0170   //
0171   // * Range constructor
0172   //
0173   //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};
0174   //   absl::flat_hash_map<int, std::string> map7(v.begin(), v.end());
0175   flat_hash_map() {}
0176   using Base::Base;
0177 
0178   // flat_hash_map::begin()
0179   //
0180   // Returns an iterator to the beginning of the `flat_hash_map`.
0181   using Base::begin;
0182 
0183   // flat_hash_map::cbegin()
0184   //
0185   // Returns a const iterator to the beginning of the `flat_hash_map`.
0186   using Base::cbegin;
0187 
0188   // flat_hash_map::cend()
0189   //
0190   // Returns a const iterator to the end of the `flat_hash_map`.
0191   using Base::cend;
0192 
0193   // flat_hash_map::end()
0194   //
0195   // Returns an iterator to the end of the `flat_hash_map`.
0196   using Base::end;
0197 
0198   // flat_hash_map::capacity()
0199   //
0200   // Returns the number of element slots (assigned, deleted, and empty)
0201   // available within the `flat_hash_map`.
0202   //
0203   // NOTE: this member function is particular to `absl::flat_hash_map` and is
0204   // not provided in the `std::unordered_map` API.
0205   using Base::capacity;
0206 
0207   // flat_hash_map::empty()
0208   //
0209   // Returns whether or not the `flat_hash_map` is empty.
0210   using Base::empty;
0211 
0212   // flat_hash_map::max_size()
0213   //
0214   // Returns the largest theoretical possible number of elements within a
0215   // `flat_hash_map` under current memory constraints. This value can be thought
0216   // of the largest value of `std::distance(begin(), end())` for a
0217   // `flat_hash_map<K, V>`.
0218   using Base::max_size;
0219 
0220   // flat_hash_map::size()
0221   //
0222   // Returns the number of elements currently within the `flat_hash_map`.
0223   using Base::size;
0224 
0225   // flat_hash_map::clear()
0226   //
0227   // Removes all elements from the `flat_hash_map`. Invalidates any references,
0228   // pointers, or iterators referring to contained elements.
0229   //
0230   // NOTE: this operation may shrink the underlying buffer. To avoid shrinking
0231   // the underlying buffer call `erase(begin(), end())`.
0232   using Base::clear;
0233 
0234   // flat_hash_map::erase()
0235   //
0236   // Erases elements within the `flat_hash_map`. Erasing does not trigger a
0237   // rehash. Overloads are listed below.
0238   //
0239   // void erase(const_iterator pos):
0240   //
0241   //   Erases the element at `position` of the `flat_hash_map`, returning
0242   //   `void`.
0243   //
0244   //   NOTE: returning `void` in this case is different than that of STL
0245   //   containers in general and `std::unordered_map` in particular (which
0246   //   return an iterator to the element following the erased element). If that
0247   //   iterator is needed, simply post increment the iterator:
0248   //
0249   //     map.erase(it++);
0250   //
0251   // iterator erase(const_iterator first, const_iterator last):
0252   //
0253   //   Erases the elements in the open interval [`first`, `last`), returning an
0254   //   iterator pointing to `last`. The special case of calling
0255   //   `erase(begin(), end())` resets the reserved growth such that if
0256   //   `reserve(N)` has previously been called and there has been no intervening
0257   //   call to `clear()`, then after calling `erase(begin(), end())`, it is safe
0258   //   to assume that inserting N elements will not cause a rehash.
0259   //
0260   // size_type erase(const key_type& key):
0261   //
0262   //   Erases the element with the matching key, if it exists, returning the
0263   //   number of elements erased (0 or 1).
0264   using Base::erase;
0265 
0266   // flat_hash_map::insert()
0267   //
0268   // Inserts an element of the specified value into the `flat_hash_map`,
0269   // returning an iterator pointing to the newly inserted element, provided that
0270   // an element with the given key does not already exist. If rehashing occurs
0271   // due to the insertion, all iterators are invalidated. Overloads are listed
0272   // below.
0273   //
0274   // std::pair<iterator,bool> insert(const init_type& value):
0275   //
0276   //   Inserts a value into the `flat_hash_map`. Returns a pair consisting of an
0277   //   iterator to the inserted element (or to the element that prevented the
0278   //   insertion) and a bool denoting whether the insertion took place.
0279   //
0280   // std::pair<iterator,bool> insert(T&& value):
0281   // std::pair<iterator,bool> insert(init_type&& value):
0282   //
0283   //   Inserts a moveable value into the `flat_hash_map`. Returns a pair
0284   //   consisting of an iterator to the inserted element (or to the element that
0285   //   prevented the insertion) and a bool denoting whether the insertion took
0286   //   place.
0287   //
0288   // iterator insert(const_iterator hint, const init_type& value):
0289   // iterator insert(const_iterator hint, T&& value):
0290   // iterator insert(const_iterator hint, init_type&& value);
0291   //
0292   //   Inserts a value, using the position of `hint` as a non-binding suggestion
0293   //   for where to begin the insertion search. Returns an iterator to the
0294   //   inserted element, or to the existing element that prevented the
0295   //   insertion.
0296   //
0297   // void insert(InputIterator first, InputIterator last):
0298   //
0299   //   Inserts a range of values [`first`, `last`).
0300   //
0301   //   NOTE: Although the STL does not specify which element may be inserted if
0302   //   multiple keys compare equivalently, for `flat_hash_map` we guarantee the
0303   //   first match is inserted.
0304   //
0305   // void insert(std::initializer_list<init_type> ilist):
0306   //
0307   //   Inserts the elements within the initializer list `ilist`.
0308   //
0309   //   NOTE: Although the STL does not specify which element may be inserted if
0310   //   multiple keys compare equivalently within the initializer list, for
0311   //   `flat_hash_map` we guarantee the first match is inserted.
0312   using Base::insert;
0313 
0314   // flat_hash_map::insert_or_assign()
0315   //
0316   // Inserts an element of the specified value into the `flat_hash_map` provided
0317   // that a value with the given key does not already exist, or replaces it with
0318   // the element value if a key for that value already exists, returning an
0319   // iterator pointing to the newly inserted element.  If rehashing occurs due
0320   // to the insertion, all existing iterators are invalidated. Overloads are
0321   // listed below.
0322   //
0323   // pair<iterator, bool> insert_or_assign(const init_type& k, T&& obj):
0324   // pair<iterator, bool> insert_or_assign(init_type&& k, T&& obj):
0325   //
0326   //   Inserts/Assigns (or moves) the element of the specified key into the
0327   //   `flat_hash_map`.
0328   //
0329   // iterator insert_or_assign(const_iterator hint,
0330   //                           const init_type& k, T&& obj):
0331   // iterator insert_or_assign(const_iterator hint, init_type&& k, T&& obj):
0332   //
0333   //   Inserts/Assigns (or moves) the element of the specified key into the
0334   //   `flat_hash_map` using the position of `hint` as a non-binding suggestion
0335   //   for where to begin the insertion search.
0336   using Base::insert_or_assign;
0337 
0338   // flat_hash_map::emplace()
0339   //
0340   // Inserts an element of the specified value by constructing it in-place
0341   // within the `flat_hash_map`, provided that no element with the given key
0342   // already exists.
0343   //
0344   // The element may be constructed even if there already is an element with the
0345   // key in the container, in which case the newly constructed element will be
0346   // destroyed immediately. Prefer `try_emplace()` unless your key is not
0347   // copyable or moveable.
0348   //
0349   // If rehashing occurs due to the insertion, all iterators are invalidated.
0350   using Base::emplace;
0351 
0352   // flat_hash_map::emplace_hint()
0353   //
0354   // Inserts an element of the specified value by constructing it in-place
0355   // within the `flat_hash_map`, using the position of `hint` as a non-binding
0356   // suggestion for where to begin the insertion search, and only inserts
0357   // provided that no element with the given key already exists.
0358   //
0359   // The element may be constructed even if there already is an element with the
0360   // key in the container, in which case the newly constructed element will be
0361   // destroyed immediately. Prefer `try_emplace()` unless your key is not
0362   // copyable or moveable.
0363   //
0364   // If rehashing occurs due to the insertion, all iterators are invalidated.
0365   using Base::emplace_hint;
0366 
0367   // flat_hash_map::try_emplace()
0368   //
0369   // Inserts an element of the specified value by constructing it in-place
0370   // within the `flat_hash_map`, provided that no element with the given key
0371   // already exists. Unlike `emplace()`, if an element with the given key
0372   // already exists, we guarantee that no element is constructed.
0373   //
0374   // If rehashing occurs due to the insertion, all iterators are invalidated.
0375   // Overloads are listed below.
0376   //
0377   //   pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):
0378   //   pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):
0379   //
0380   // Inserts (via copy or move) the element of the specified key into the
0381   // `flat_hash_map`.
0382   //
0383   //   iterator try_emplace(const_iterator hint,
0384   //                        const key_type& k, Args&&... args):
0385   //   iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args):
0386   //
0387   // Inserts (via copy or move) the element of the specified key into the
0388   // `flat_hash_map` using the position of `hint` as a non-binding suggestion
0389   // for where to begin the insertion search.
0390   //
0391   // All `try_emplace()` overloads make the same guarantees regarding rvalue
0392   // arguments as `std::unordered_map::try_emplace()`, namely that these
0393   // functions will not move from rvalue arguments if insertions do not happen.
0394   using Base::try_emplace;
0395 
0396   // flat_hash_map::extract()
0397   //
0398   // Extracts the indicated element, erasing it in the process, and returns it
0399   // as a C++17-compatible node handle. Overloads are listed below.
0400   //
0401   // node_type extract(const_iterator position):
0402   //
0403   //   Extracts the key,value pair of the element at the indicated position and
0404   //   returns a node handle owning that extracted data.
0405   //
0406   // node_type extract(const key_type& x):
0407   //
0408   //   Extracts the key,value pair of the element with a key matching the passed
0409   //   key value and returns a node handle owning that extracted data. If the
0410   //   `flat_hash_map` does not contain an element with a matching key, this
0411   //   function returns an empty node handle.
0412   //
0413   // NOTE: when compiled in an earlier version of C++ than C++17,
0414   // `node_type::key()` returns a const reference to the key instead of a
0415   // mutable reference. We cannot safely return a mutable reference without
0416   // std::launder (which is not available before C++17).
0417   using Base::extract;
0418 
0419   // flat_hash_map::merge()
0420   //
0421   // Extracts elements from a given `source` flat hash map into this
0422   // `flat_hash_map`. If the destination `flat_hash_map` already contains an
0423   // element with an equivalent key, that element is not extracted.
0424   using Base::merge;
0425 
0426   // flat_hash_map::swap(flat_hash_map& other)
0427   //
0428   // Exchanges the contents of this `flat_hash_map` with those of the `other`
0429   // flat hash map, avoiding invocation of any move, copy, or swap operations on
0430   // individual elements.
0431   //
0432   // All iterators and references on the `flat_hash_map` remain valid, excepting
0433   // for the past-the-end iterator, which is invalidated.
0434   //
0435   // `swap()` requires that the flat hash map's hashing and key equivalence
0436   // functions be Swappable, and are exchanged using unqualified calls to
0437   // non-member `swap()`. If the map's allocator has
0438   // `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
0439   // set to `true`, the allocators are also exchanged using an unqualified call
0440   // to non-member `swap()`; otherwise, the allocators are not swapped.
0441   using Base::swap;
0442 
0443   // flat_hash_map::rehash(count)
0444   //
0445   // Rehashes the `flat_hash_map`, setting the number of slots to be at least
0446   // the passed value. If the new number of slots increases the load factor more
0447   // than the current maximum load factor
0448   // (`count` < `size()` / `max_load_factor()`), then the new number of slots
0449   // will be at least `size()` / `max_load_factor()`.
0450   //
0451   // To force a rehash, pass rehash(0).
0452   //
0453   // NOTE: unlike behavior in `std::unordered_map`, references are also
0454   // invalidated upon a `rehash()`.
0455   using Base::rehash;
0456 
0457   // flat_hash_map::reserve(count)
0458   //
0459   // Sets the number of slots in the `flat_hash_map` to the number needed to
0460   // accommodate at least `count` total elements without exceeding the current
0461   // maximum load factor, and may rehash the container if needed.
0462   using Base::reserve;
0463 
0464   // flat_hash_map::at()
0465   //
0466   // Returns a reference to the mapped value of the element with key equivalent
0467   // to the passed key.
0468   using Base::at;
0469 
0470   // flat_hash_map::contains()
0471   //
0472   // Determines whether an element with a key comparing equal to the given `key`
0473   // exists within the `flat_hash_map`, returning `true` if so or `false`
0474   // otherwise.
0475   using Base::contains;
0476 
0477   // flat_hash_map::count(const Key& key) const
0478   //
0479   // Returns the number of elements with a key comparing equal to the given
0480   // `key` within the `flat_hash_map`. note that this function will return
0481   // either `1` or `0` since duplicate keys are not allowed within a
0482   // `flat_hash_map`.
0483   using Base::count;
0484 
0485   // flat_hash_map::equal_range()
0486   //
0487   // Returns a closed range [first, last], defined by a `std::pair` of two
0488   // iterators, containing all elements with the passed key in the
0489   // `flat_hash_map`.
0490   using Base::equal_range;
0491 
0492   // flat_hash_map::find()
0493   //
0494   // Finds an element with the passed `key` within the `flat_hash_map`.
0495   using Base::find;
0496 
0497   // flat_hash_map::operator[]()
0498   //
0499   // Returns a reference to the value mapped to the passed key within the
0500   // `flat_hash_map`, performing an `insert()` if the key does not already
0501   // exist.
0502   //
0503   // If an insertion occurs and results in a rehashing of the container, all
0504   // iterators are invalidated. Otherwise iterators are not affected and
0505   // references are not invalidated. Overloads are listed below.
0506   //
0507   // T& operator[](const Key& key):
0508   //
0509   //   Inserts an init_type object constructed in-place if the element with the
0510   //   given key does not exist.
0511   //
0512   // T& operator[](Key&& key):
0513   //
0514   //   Inserts an init_type object constructed in-place provided that an element
0515   //   with the given key does not exist.
0516   using Base::operator[];
0517 
0518   // flat_hash_map::bucket_count()
0519   //
0520   // Returns the number of "buckets" within the `flat_hash_map`. Note that
0521   // because a flat hash map contains all elements within its internal storage,
0522   // this value simply equals the current capacity of the `flat_hash_map`.
0523   using Base::bucket_count;
0524 
0525   // flat_hash_map::load_factor()
0526   //
0527   // Returns the current load factor of the `flat_hash_map` (the average number
0528   // of slots occupied with a value within the hash map).
0529   using Base::load_factor;
0530 
0531   // flat_hash_map::max_load_factor()
0532   //
0533   // Manages the maximum load factor of the `flat_hash_map`. Overloads are
0534   // listed below.
0535   //
0536   // float flat_hash_map::max_load_factor()
0537   //
0538   //   Returns the current maximum load factor of the `flat_hash_map`.
0539   //
0540   // void flat_hash_map::max_load_factor(float ml)
0541   //
0542   //   Sets the maximum load factor of the `flat_hash_map` to the passed value.
0543   //
0544   //   NOTE: This overload is provided only for API compatibility with the STL;
0545   //   `flat_hash_map` will ignore any set load factor and manage its rehashing
0546   //   internally as an implementation detail.
0547   using Base::max_load_factor;
0548 
0549   // flat_hash_map::get_allocator()
0550   //
0551   // Returns the allocator function associated with this `flat_hash_map`.
0552   using Base::get_allocator;
0553 
0554   // flat_hash_map::hash_function()
0555   //
0556   // Returns the hashing function used to hash the keys within this
0557   // `flat_hash_map`.
0558   using Base::hash_function;
0559 
0560   // flat_hash_map::key_eq()
0561   //
0562   // Returns the function used for comparing keys equality.
0563   using Base::key_eq;
0564 };
0565 
0566 // erase_if(flat_hash_map<>, Pred)
0567 //
0568 // Erases all elements that satisfy the predicate `pred` from the container `c`.
0569 // Returns the number of erased elements.
0570 template <typename K, typename V, typename H, typename E, typename A,
0571           typename Predicate>
0572 typename flat_hash_map<K, V, H, E, A>::size_type erase_if(
0573     flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
0574   return container_internal::EraseIf(pred, &c);
0575 }
0576 
0577 namespace container_internal {
0578 
0579 // c_for_each_fast(flat_hash_map<>, Function)
0580 //
0581 // Container-based version of the <algorithm> `std::for_each()` function to
0582 // apply a function to a container's elements.
0583 // There is no guarantees on the order of the function calls.
0584 // Erasure and/or insertion of elements in the function is not allowed.
0585 template <typename K, typename V, typename H, typename E, typename A,
0586           typename Function>
0587 decay_t<Function> c_for_each_fast(const flat_hash_map<K, V, H, E, A>& c,
0588                                   Function&& f) {
0589   container_internal::ForEach(f, &c);
0590   return f;
0591 }
0592 template <typename K, typename V, typename H, typename E, typename A,
0593           typename Function>
0594 decay_t<Function> c_for_each_fast(flat_hash_map<K, V, H, E, A>& c,
0595                                   Function&& f) {
0596   container_internal::ForEach(f, &c);
0597   return f;
0598 }
0599 template <typename K, typename V, typename H, typename E, typename A,
0600           typename Function>
0601 decay_t<Function> c_for_each_fast(flat_hash_map<K, V, H, E, A>&& c,
0602                                   Function&& f) {
0603   container_internal::ForEach(f, &c);
0604   return f;
0605 }
0606 
0607 }  // namespace container_internal
0608 
0609 namespace container_internal {
0610 
0611 template <class K, class V>
0612 struct FlatHashMapPolicy {
0613   using slot_policy = container_internal::map_slot_policy<K, V>;
0614   using slot_type = typename slot_policy::slot_type;
0615   using key_type = K;
0616   using mapped_type = V;
0617   using init_type = std::pair</*non const*/ key_type, mapped_type>;
0618 
0619   template <class Allocator, class... Args>
0620   static void construct(Allocator* alloc, slot_type* slot, Args&&... args) {
0621     slot_policy::construct(alloc, slot, std::forward<Args>(args)...);
0622   }
0623 
0624   // Returns std::true_type in case destroy is trivial.
0625   template <class Allocator>
0626   static auto destroy(Allocator* alloc, slot_type* slot) {
0627     return slot_policy::destroy(alloc, slot);
0628   }
0629 
0630   template <class Allocator>
0631   static auto transfer(Allocator* alloc, slot_type* new_slot,
0632                        slot_type* old_slot) {
0633     return slot_policy::transfer(alloc, new_slot, old_slot);
0634   }
0635 
0636   template <class F, class... Args>
0637   static decltype(absl::container_internal::DecomposePair(
0638       std::declval<F>(), std::declval<Args>()...))
0639   apply(F&& f, Args&&... args) {
0640     return absl::container_internal::DecomposePair(std::forward<F>(f),
0641                                                    std::forward<Args>(args)...);
0642   }
0643 
0644   template <class Hash>
0645   static constexpr HashSlotFn get_hash_slot_fn() {
0646     return memory_internal::IsLayoutCompatible<K, V>::value
0647                ? &TypeErasedApplyToSlotFn<Hash, K>
0648                : nullptr;
0649   }
0650 
0651   static size_t space_used(const slot_type*) { return 0; }
0652 
0653   static std::pair<const K, V>& element(slot_type* slot) { return slot->value; }
0654 
0655   static V& value(std::pair<const K, V>* kv) { return kv->second; }
0656   static const V& value(const std::pair<const K, V>* kv) { return kv->second; }
0657 };
0658 
0659 }  // namespace container_internal
0660 
0661 namespace container_algorithm_internal {
0662 
0663 // Specialization of trait in absl/algorithm/container.h
0664 template <class Key, class T, class Hash, class KeyEqual, class Allocator>
0665 struct IsUnorderedContainer<
0666     absl::flat_hash_map<Key, T, Hash, KeyEqual, Allocator>> : std::true_type {};
0667 
0668 }  // namespace container_algorithm_internal
0669 
0670 ABSL_NAMESPACE_END
0671 }  // namespace absl
0672 
0673 #endif  // ABSL_CONTAINER_FLAT_HASH_MAP_H_