THUAI6/CAPI/cpp/grpc/include/absl/container/flat_hash_set.h

// 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_set.h
// -----------------------------------------------------------------------------
//
// An `absl::flat_hash_set<T>` is an unordered associative container designed to
// be a more efficient replacement for `std::unordered_set`. Like
// `unordered_set`, search, insertion, and deletion of set elements can be done
// as an `O(1)` operation. However, `flat_hash_set` (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 set should be a set of type
// `flat_hash_set`.
#ifndef ABSL_CONTAINER_FLAT_HASH_SET_H_
#define ABSL_CONTAINER_FLAT_HASH_SET_H_

#include <type_traits>
#include <utility>

#include "absl/algorithm/container.h"
#include "absl/base/macros.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_set.h"            // IWYU pragma: export
#include "absl/memory/memory.h"

namespace absl
{
    ABSL_NAMESPACE_BEGIN
    namespace container_internal
    {
        template<typename T>
        struct FlatHashSetPolicy;
    }  // namespace container_internal

    // -----------------------------------------------------------------------------
    // absl::flat_hash_set
    // -----------------------------------------------------------------------------
    //
    // An `absl::flat_hash_set<T>` 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_set<T>` with the
    // following notable differences:
    //
    // * Requires keys that are CopyConstructible
    // * Supports heterogeneous lookup, through `find()` and `insert()`, provided
    //   that the set 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 set.
    // * Returns `void` from the `erase(iterator)` overload.
    //
    // By default, `flat_hash_set` 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_set`.
    // 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.
    //
    // Using `absl::flat_hash_set` at interface boundaries in dynamically loaded
    // libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may
    // be randomized across dynamically loaded libraries.
    //
    // NOTE: A `flat_hash_set` stores its keys directly inside its implementation
    // array to avoid memory indirection. Because a `flat_hash_set` is designed to
    // move data when rehashed, set keys will not retain pointer stability. If you
    // require pointer stability, consider using
    // `absl::flat_hash_set<std::unique_ptr<T>>`. If your type is not moveable and
    // you require pointer stability, consider `absl::node_hash_set` instead.
    //
    // Example:
    //
    //   // Create a flat hash set of three strings
    //   absl::flat_hash_set<std::string> ducks =
    //     {"huey", "dewey", "louie"};
    //
    //  // Insert a new element into the flat hash set
    //  ducks.insert("donald");
    //
    //  // Force a rehash of the flat hash set
    //  ducks.rehash(0);
    //
    //  // See if "dewey" is present
    //  if (ducks.contains("dewey")) {
    //    std::cout << "We found dewey!" << std::endl;
    //  }
    template<class T, class Hash = absl::container_internal::hash_default_hash<T>, class Eq = absl::container_internal::hash_default_eq<T>, class Allocator = std::allocator<T>>
    class flat_hash_set : public absl::container_internal::raw_hash_set<absl::container_internal::FlatHashSetPolicy<T>, Hash, Eq, Allocator>
    {
        using Base = typename flat_hash_set::raw_hash_set;

    public:
        // Constructors and Assignment Operators
        //
        // A flat_hash_set supports the same overload set as `std::unordered_set`
        // for construction and assignment:
        //
        // *  Default constructor
        //
        //    // No allocation for the table's elements is made.
        //    absl::flat_hash_set<std::string> set1;
        //
        // * Initializer List constructor
        //
        //   absl::flat_hash_set<std::string> set2 =
        //       {{"huey"}, {"dewey"}, {"louie"},};
        //
        // * Copy constructor
        //
        //   absl::flat_hash_set<std::string> set3(set2);
        //
        // * Copy assignment operator
        //
        //  // Hash functor and Comparator are copied as well
        //  absl::flat_hash_set<std::string> set4;
        //  set4 = set3;
        //
        // * Move constructor
        //
        //   // Move is guaranteed efficient
        //   absl::flat_hash_set<std::string> set5(std::move(set4));
        //
        // * Move assignment operator
        //
        //   // May be efficient if allocators are compatible
        //   absl::flat_hash_set<std::string> set6;
        //   set6 = std::move(set5);
        //
        // * Range constructor
        //
        //   std::vector<std::string> v = {"a", "b"};
        //   absl::flat_hash_set<std::string> set7(v.begin(), v.end());
        flat_hash_set()
        {
        }
        using Base::Base;

        // flat_hash_set::begin()
        //
        // Returns an iterator to the beginning of the `flat_hash_set`.
        using Base::begin;

        // flat_hash_set::cbegin()
        //
        // Returns a const iterator to the beginning of the `flat_hash_set`.
        using Base::cbegin;

        // flat_hash_set::cend()
        //
        // Returns a const iterator to the end of the `flat_hash_set`.
        using Base::cend;

        // flat_hash_set::end()
        //
        // Returns an iterator to the end of the `flat_hash_set`.
        using Base::end;

        // flat_hash_set::capacity()
        //
        // Returns the number of element slots (assigned, deleted, and empty)
        // available within the `flat_hash_set`.
        //
        // NOTE: this member function is particular to `absl::flat_hash_set` and is
        // not provided in the `std::unordered_set` API.
        using Base::capacity;

        // flat_hash_set::empty()
        //
        // Returns whether or not the `flat_hash_set` is empty.
        using Base::empty;

        // flat_hash_set::max_size()
        //
        // Returns the largest theoretical possible number of elements within a
        // `flat_hash_set` under current memory constraints. This value can be thought
        // of the largest value of `std::distance(begin(), end())` for a
        // `flat_hash_set<T>`.
        using Base::max_size;

        // flat_hash_set::size()
        //
        // Returns the number of elements currently within the `flat_hash_set`.
        using Base::size;

        // flat_hash_set::clear()
        //
        // Removes all elements from the `flat_hash_set`. 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_set::erase()
        //
        // Erases elements within the `flat_hash_set`. Erasing does not trigger a
        // rehash. Overloads are listed below.
        //
        // void erase(const_iterator pos):
        //
        //   Erases the element at `position` of the `flat_hash_set`, returning
        //   `void`.
        //
        //   NOTE: returning `void` in this case is different than that of STL
        //   containers in general and `std::unordered_set` in particular (which
        //   return an iterator to the element following the erased element). If that
        //   iterator is needed, simply post increment the iterator:
        //
        //     set.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_set::insert()
        //
        // Inserts an element of the specified value into the `flat_hash_set`,
        // 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 T& value):
        //
        //   Inserts a value into the `flat_hash_set`. 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):
        //
        //   Inserts a moveable value into the `flat_hash_set`. 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 T& value):
        // iterator insert(const_iterator hint, T&& 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_set` we guarantee the
        //   first match is inserted.
        //
        // void insert(std::initializer_list<T> 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_set` we guarantee the first match is inserted.
        using Base::insert;

        // flat_hash_set::emplace()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `flat_hash_set`, 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.
        //
        // If rehashing occurs due to the insertion, all iterators are invalidated.
        using Base::emplace;

        // flat_hash_set::emplace_hint()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `flat_hash_set`, 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.
        //
        // If rehashing occurs due to the insertion, all iterators are invalidated.
        using Base::emplace_hint;

        // flat_hash_set::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 element at the indicated position and returns a node handle
        //   owning that extracted data.
        //
        // node_type extract(const key_type& x):
        //
        //   Extracts the element with the key matching the passed key value and
        //   returns a node handle owning that extracted data. If the `flat_hash_set`
        //   does not contain an element with a matching key, this function returns an
        //   empty node handle.
        using Base::extract;

        // flat_hash_set::merge()
        //
        // Extracts elements from a given `source` flat hash set into this
        // `flat_hash_set`. If the destination `flat_hash_set` already contains an
        // element with an equivalent key, that element is not extracted.
        using Base::merge;

        // flat_hash_set::swap(flat_hash_set& other)
        //
        // Exchanges the contents of this `flat_hash_set` with those of the `other`
        // flat hash set, avoiding invocation of any move, copy, or swap operations on
        // individual elements.
        //
        // All iterators and references on the `flat_hash_set` remain valid, excepting
        // for the past-the-end iterator, which is invalidated.
        //
        // `swap()` requires that the flat hash set's hashing and key equivalence
        // functions be Swappable, and are exchaged using unqualified calls to
        // non-member `swap()`. If the set'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_set::rehash(count)
        //
        // Rehashes the `flat_hash_set`, 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_set`, references are also
        // invalidated upon a `rehash()`.
        using Base::rehash;

        // flat_hash_set::reserve(count)
        //
        // Sets the number of slots in the `flat_hash_set` to the number needed to
        // accommodate at least `count` total elements without exceeding the current
        // maximum load factor, and may rehash the container if needed.
        using Base::reserve;

        // flat_hash_set::contains()
        //
        // Determines whether an element comparing equal to the given `key` exists
        // within the `flat_hash_set`, returning `true` if so or `false` otherwise.
        using Base::contains;

        // flat_hash_set::count(const Key& key) const
        //
        // Returns the number of elements comparing equal to the given `key` within
        // the `flat_hash_set`. note that this function will return either `1` or `0`
        // since duplicate elements are not allowed within a `flat_hash_set`.
        using Base::count;

        // flat_hash_set::equal_range()
        //
        // Returns a closed range [first, last], defined by a `std::pair` of two
        // iterators, containing all elements with the passed key in the
        // `flat_hash_set`.
        using Base::equal_range;

        // flat_hash_set::find()
        //
        // Finds an element with the passed `key` within the `flat_hash_set`.
        using Base::find;

        // flat_hash_set::bucket_count()
        //
        // Returns the number of "buckets" within the `flat_hash_set`. Note that
        // because a flat hash set contains all elements within its internal storage,
        // this value simply equals the current capacity of the `flat_hash_set`.
        using Base::bucket_count;

        // flat_hash_set::load_factor()
        //
        // Returns the current load factor of the `flat_hash_set` (the average number
        // of slots occupied with a value within the hash set).
        using Base::load_factor;

        // flat_hash_set::max_load_factor()
        //
        // Manages the maximum load factor of the `flat_hash_set`. Overloads are
        // listed below.
        //
        // float flat_hash_set::max_load_factor()
        //
        //   Returns the current maximum load factor of the `flat_hash_set`.
        //
        // void flat_hash_set::max_load_factor(float ml)
        //
        //   Sets the maximum load factor of the `flat_hash_set` to the passed value.
        //
        //   NOTE: This overload is provided only for API compatibility with the STL;
        //   `flat_hash_set` will ignore any set load factor and manage its rehashing
        //   internally as an implementation detail.
        using Base::max_load_factor;

        // flat_hash_set::get_allocator()
        //
        // Returns the allocator function associated with this `flat_hash_set`.
        using Base::get_allocator;

        // flat_hash_set::hash_function()
        //
        // Returns the hashing function used to hash the keys within this
        // `flat_hash_set`.
        using Base::hash_function;

        // flat_hash_set::key_eq()
        //
        // Returns the function used for comparing keys equality.
        using Base::key_eq;
    };

    // erase_if(flat_hash_set<>, Pred)
    //
    // Erases all elements that satisfy the predicate `pred` from the container `c`.
    // Returns the number of erased elements.
    template<typename T, typename H, typename E, typename A, typename Predicate>
    typename flat_hash_set<T, H, E, A>::size_type erase_if(
        flat_hash_set<T, H, E, A>& c, Predicate pred
    )
    {
        return container_internal::EraseIf(pred, &c);
    }

    namespace container_internal
    {

        template<class T>
        struct FlatHashSetPolicy
        {
            using slot_type = T;
            using key_type = T;
            using init_type = T;
            using constant_iterators = std::true_type;

            template<class Allocator, class... Args>
            static void construct(Allocator* alloc, slot_type* slot, Args&&... args)
            {
                absl::allocator_traits<Allocator>::construct(*alloc, slot, std::forward<Args>(args)...);
            }

            template<class Allocator>
            static void destroy(Allocator* alloc, slot_type* slot)
            {
                absl::allocator_traits<Allocator>::destroy(*alloc, slot);
            }

            template<class Allocator>
            static void transfer(Allocator* alloc, slot_type* new_slot, slot_type* old_slot)
            {
                construct(alloc, new_slot, std::move(*old_slot));
                destroy(alloc, old_slot);
            }

            static T& element(slot_type* slot)
            {
                return *slot;
            }

            template<class F, class... Args>
            static decltype(absl::container_internal::DecomposeValue(
                std::declval<F>(), std::declval<Args>()...
            ))
                apply(F&& f, Args&&... args)
            {
                return absl::container_internal::DecomposeValue(
                    std::forward<F>(f), std::forward<Args>(args)...
                );
            }

            static size_t space_used(const T*)
            {
                return 0;
            }
        };
    }  // namespace container_internal

    namespace container_algorithm_internal
    {

        // Specialization of trait in absl/algorithm/container.h
        template<class Key, class Hash, class KeyEqual, class Allocator>
        struct IsUnorderedContainer<absl::flat_hash_set<Key, Hash, KeyEqual, Allocator>> : std::true_type
        {
        };

    }  // namespace container_algorithm_internal

    ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CONTAINER_FLAT_HASH_SET_H_