THUAI6/CAPI/cpp/grpc/include/absl/container/btree_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: btree_set.h
// -----------------------------------------------------------------------------
//
// This header file defines B-tree sets: sorted associative containers of
// values.
//
//     * `absl::btree_set<>`
//     * `absl::btree_multiset<>`
//
// These B-tree types are similar to the corresponding types in the STL
// (`std::set` and `std::multiset`) and generally conform to the STL interfaces
// of those types. However, because they are implemented using B-trees, they
// are more efficient in most situations.
//
// Unlike `std::set` and `std::multiset`, which are commonly implemented using
// red-black tree nodes, B-tree sets use more generic B-tree nodes able to hold
// multiple values per node. Holding multiple values per node often makes
// B-tree sets perform better than their `std::set` counterparts, because
// multiple entries can be checked within the same cache hit.
//
// However, these types should not be considered drop-in replacements for
// `std::set` and `std::multiset` as there are some API differences, which are
// noted in this header file. The most consequential differences with respect to
// migrating to b-tree from the STL types are listed in the next paragraph.
// Other API differences are minor.
//
// Importantly, insertions and deletions may invalidate outstanding iterators,
// pointers, and references to elements. Such invalidations are typically only
// an issue if insertion and deletion operations are interleaved with the use of
// more than one iterator, pointer, or reference simultaneously. For this
// reason, `insert()` and `erase()` return a valid iterator at the current
// position.

#ifndef ABSL_CONTAINER_BTREE_SET_H_
#define ABSL_CONTAINER_BTREE_SET_H_

#include "absl/container/internal/btree.h"            // IWYU pragma: export
#include "absl/container/internal/btree_container.h"  // IWYU pragma: export

namespace absl
{
    ABSL_NAMESPACE_BEGIN

    namespace container_internal
    {

        template<typename Key>
        struct set_slot_policy;

        template<typename Key, typename Compare, typename Alloc, int TargetNodeSize, bool IsMulti>
        struct set_params;

    }  // namespace container_internal

    // absl::btree_set<>
    //
    // An `absl::btree_set<K>` is an ordered associative container of unique key
    // values designed to be a more efficient replacement for `std::set` (in most
    // cases).
    //
    // Keys are sorted using an (optional) comparison function, which defaults to
    // `std::less<K>`.
    //
    // An `absl::btree_set<K>` uses a default allocator of `std::allocator<K>` to
    // allocate (and deallocate) nodes, and construct and destruct values within
    // those nodes. You may instead specify a custom allocator `A` (which in turn
    // requires specifying a custom comparator `C`) as in
    // `absl::btree_set<K, C, A>`.
    //
    template<typename Key, typename Compare = std::less<Key>, typename Alloc = std::allocator<Key>>
    class btree_set : public container_internal::btree_set_container<container_internal::btree<container_internal::set_params<Key, Compare, Alloc, /*TargetNodeSize=*/256,
                                                                                                                              /*IsMulti=*/false>>>
    {
        using Base = typename btree_set::btree_set_container;

    public:
        // Constructors and Assignment Operators
        //
        // A `btree_set` supports the same overload set as `std::set`
        // for construction and assignment:
        //
        // * Default constructor
        //
        //   absl::btree_set<std::string> set1;
        //
        // * Initializer List constructor
        //
        //   absl::btree_set<std::string> set2 =
        //       {{"huey"}, {"dewey"}, {"louie"},};
        //
        // * Copy constructor
        //
        //   absl::btree_set<std::string> set3(set2);
        //
        // * Copy assignment operator
        //
        //  absl::btree_set<std::string> set4;
        //  set4 = set3;
        //
        // * Move constructor
        //
        //   // Move is guaranteed efficient
        //   absl::btree_set<std::string> set5(std::move(set4));
        //
        // * Move assignment operator
        //
        //   // May be efficient if allocators are compatible
        //   absl::btree_set<std::string> set6;
        //   set6 = std::move(set5);
        //
        // * Range constructor
        //
        //   std::vector<std::string> v = {"a", "b"};
        //   absl::btree_set<std::string> set7(v.begin(), v.end());
        btree_set()
        {
        }
        using Base::Base;

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

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

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

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

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

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

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

        // btree_set::clear()
        //
        // Removes all elements from the `btree_set`. Invalidates any references,
        // pointers, or iterators referring to contained elements.
        using Base::clear;

        // btree_set::erase()
        //
        // Erases elements within the `btree_set`. Overloads are listed below.
        //
        // iterator erase(iterator position):
        // iterator erase(const_iterator position):
        //
        //   Erases the element at `position` of the `btree_set`, returning
        //   the iterator pointing to the element after the one that was erased
        //   (or end() if none exists).
        //
        // iterator erase(const_iterator first, const_iterator last):
        //
        //   Erases the elements in the open interval [`first`, `last`), returning
        //   the iterator pointing to the element after the interval that was erased
        //   (or end() if none exists).
        //
        // template <typename K> size_type erase(const K& key):
        //
        //   Erases the element with the matching key, if it exists, returning the
        //   number of elements erased (0 or 1).
        using Base::erase;

        // btree_set::insert()
        //
        // Inserts an element of the specified value into the `btree_set`,
        // returning an iterator pointing to the newly inserted element, provided that
        // an element with the given key does not already exist. If an insertion
        // occurs, any references, pointers, or iterators are invalidated.
        // Overloads are listed below.
        //
        // std::pair<iterator,bool> insert(const value_type& value):
        //
        //   Inserts a value into the `btree_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(value_type&& value):
        //
        //   Inserts a moveable value into the `btree_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 value_type& value):
        // iterator insert(const_iterator hint, value_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`).
        //
        // void insert(std::initializer_list<init_type> ilist):
        //
        //   Inserts the elements within the initializer list `ilist`.
        using Base::insert;

        // btree_set::emplace()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `btree_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 an insertion occurs, any references, pointers, or iterators are
        // invalidated.
        using Base::emplace;

        // btree_set::emplace_hint()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `btree_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 an insertion occurs, any references, pointers, or iterators are
        // invalidated.
        using Base::emplace_hint;

        // btree_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.
        //
        // template <typename K> node_type extract(const K& k):
        //
        //   Extracts the element with the key matching the passed key value and
        //   returns a node handle owning that extracted data. If the `btree_set`
        //   does not contain an element with a matching key, this function returns an
        //   empty node handle.
        //
        // NOTE: In this context, `node_type` refers to the C++17 concept of a
        // move-only type that owns and provides access to the elements in associative
        // containers (https://en.cppreference.com/w/cpp/container/node_handle).
        // It does NOT refer to the data layout of the underlying btree.
        using Base::extract;

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

        // btree_set::swap(btree_set& other)
        //
        // Exchanges the contents of this `btree_set` with those of the `other`
        // btree_set, avoiding invocation of any move, copy, or swap operations on
        // individual elements.
        //
        // All iterators and references on the `btree_set` remain valid, excepting
        // for the past-the-end iterator, which is invalidated.
        using Base::swap;

        // btree_set::contains()
        //
        // template <typename K> bool contains(const K& key) const:
        //
        // Determines whether an element comparing equal to the given `key` exists
        // within the `btree_set`, returning `true` if so or `false` otherwise.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::contains;

        // btree_set::count()
        //
        // template <typename K> size_type count(const K& key) const:
        //
        // Returns the number of elements comparing equal to the given `key` within
        // the `btree_set`. Note that this function will return either `1` or `0`
        // since duplicate elements are not allowed within a `btree_set`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::count;

        // btree_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
        // `btree_set`.
        using Base::equal_range;

        // btree_set::find()
        //
        // template <typename K> iterator find(const K& key):
        // template <typename K> const_iterator find(const K& key) const:
        //
        // Finds an element with the passed `key` within the `btree_set`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::find;

        // btree_set::lower_bound()
        //
        // template <typename K> iterator lower_bound(const K& key):
        // template <typename K> const_iterator lower_bound(const K& key) const:
        //
        // Finds the first element that is not less than `key` within the `btree_set`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::lower_bound;

        // btree_set::upper_bound()
        //
        // template <typename K> iterator upper_bound(const K& key):
        // template <typename K> const_iterator upper_bound(const K& key) const:
        //
        // Finds the first element that is greater than `key` within the `btree_set`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::upper_bound;

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

        // btree_set::key_comp();
        //
        // Returns the key comparator associated with this `btree_set`.
        using Base::key_comp;

        // btree_set::value_comp();
        //
        // Returns the value comparator associated with this `btree_set`. The keys to
        // sort the elements are the values themselves, therefore `value_comp` and its
        // sibling member function `key_comp` are equivalent.
        using Base::value_comp;
    };

    // absl::swap(absl::btree_set<>, absl::btree_set<>)
    //
    // Swaps the contents of two `absl::btree_set` containers.
    template<typename K, typename C, typename A>
    void swap(btree_set<K, C, A>& x, btree_set<K, C, A>& y)
    {
        return x.swap(y);
    }

    // absl::erase_if(absl::btree_set<>, Pred)
    //
    // Erases all elements that satisfy the predicate pred from the container.
    // Returns the number of erased elements.
    template<typename K, typename C, typename A, typename Pred>
    typename btree_set<K, C, A>::size_type erase_if(btree_set<K, C, A>& set, Pred pred)
    {
        return container_internal::btree_access::erase_if(set, std::move(pred));
    }

    // absl::btree_multiset<>
    //
    // An `absl::btree_multiset<K>` is an ordered associative container of
    // keys and associated values designed to be a more efficient replacement
    // for `std::multiset` (in most cases). Unlike `absl::btree_set`, a B-tree
    // multiset allows equivalent elements.
    //
    // Keys are sorted using an (optional) comparison function, which defaults to
    // `std::less<K>`.
    //
    // An `absl::btree_multiset<K>` uses a default allocator of `std::allocator<K>`
    // to allocate (and deallocate) nodes, and construct and destruct values within
    // those nodes. You may instead specify a custom allocator `A` (which in turn
    // requires specifying a custom comparator `C`) as in
    // `absl::btree_multiset<K, C, A>`.
    //
    template<typename Key, typename Compare = std::less<Key>, typename Alloc = std::allocator<Key>>
    class btree_multiset : public container_internal::btree_multiset_container<container_internal::btree<container_internal::set_params<Key, Compare, Alloc, /*TargetNodeSize=*/256,
                                                                                                                                        /*IsMulti=*/true>>>
    {
        using Base = typename btree_multiset::btree_multiset_container;

    public:
        // Constructors and Assignment Operators
        //
        // A `btree_multiset` supports the same overload set as `std::set`
        // for construction and assignment:
        //
        // * Default constructor
        //
        //   absl::btree_multiset<std::string> set1;
        //
        // * Initializer List constructor
        //
        //   absl::btree_multiset<std::string> set2 =
        //       {{"huey"}, {"dewey"}, {"louie"},};
        //
        // * Copy constructor
        //
        //   absl::btree_multiset<std::string> set3(set2);
        //
        // * Copy assignment operator
        //
        //  absl::btree_multiset<std::string> set4;
        //  set4 = set3;
        //
        // * Move constructor
        //
        //   // Move is guaranteed efficient
        //   absl::btree_multiset<std::string> set5(std::move(set4));
        //
        // * Move assignment operator
        //
        //   // May be efficient if allocators are compatible
        //   absl::btree_multiset<std::string> set6;
        //   set6 = std::move(set5);
        //
        // * Range constructor
        //
        //   std::vector<std::string> v = {"a", "b"};
        //   absl::btree_multiset<std::string> set7(v.begin(), v.end());
        btree_multiset()
        {
        }
        using Base::Base;

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

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

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

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

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

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

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

        // btree_multiset::clear()
        //
        // Removes all elements from the `btree_multiset`. Invalidates any references,
        // pointers, or iterators referring to contained elements.
        using Base::clear;

        // btree_multiset::erase()
        //
        // Erases elements within the `btree_multiset`. Overloads are listed below.
        //
        // iterator erase(iterator position):
        // iterator erase(const_iterator position):
        //
        //   Erases the element at `position` of the `btree_multiset`, returning
        //   the iterator pointing to the element after the one that was erased
        //   (or end() if none exists).
        //
        // iterator erase(const_iterator first, const_iterator last):
        //
        //   Erases the elements in the open interval [`first`, `last`), returning
        //   the iterator pointing to the element after the interval that was erased
        //   (or end() if none exists).
        //
        // template <typename K> size_type erase(const K& key):
        //
        //   Erases the elements matching the key, if any exist, returning the
        //   number of elements erased.
        using Base::erase;

        // btree_multiset::insert()
        //
        // Inserts an element of the specified value into the `btree_multiset`,
        // returning an iterator pointing to the newly inserted element.
        // Any references, pointers, or iterators are invalidated.  Overloads are
        // listed below.
        //
        // iterator insert(const value_type& value):
        //
        //   Inserts a value into the `btree_multiset`, returning an iterator to the
        //   inserted element.
        //
        // iterator insert(value_type&& value):
        //
        //   Inserts a moveable value into the `btree_multiset`, returning an iterator
        //   to the inserted element.
        //
        // iterator insert(const_iterator hint, const value_type& value):
        // iterator insert(const_iterator hint, value_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.
        //
        // void insert(InputIterator first, InputIterator last):
        //
        //   Inserts a range of values [`first`, `last`).
        //
        // void insert(std::initializer_list<init_type> ilist):
        //
        //   Inserts the elements within the initializer list `ilist`.
        using Base::insert;

        // btree_multiset::emplace()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `btree_multiset`. Any references, pointers, or iterators are
        // invalidated.
        using Base::emplace;

        // btree_multiset::emplace_hint()
        //
        // Inserts an element of the specified value by constructing it in-place
        // within the `btree_multiset`, using the position of `hint` as a non-binding
        // suggestion for where to begin the insertion search.
        //
        // Any references, pointers, or iterators are invalidated.
        using Base::emplace_hint;

        // btree_multiset::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.
        //
        // template <typename K> node_type extract(const K& k):
        //
        //   Extracts the element with the key matching the passed key value and
        //   returns a node handle owning that extracted data. If the `btree_multiset`
        //   does not contain an element with a matching key, this function returns an
        //   empty node handle.
        //
        // NOTE: In this context, `node_type` refers to the C++17 concept of a
        // move-only type that owns and provides access to the elements in associative
        // containers (https://en.cppreference.com/w/cpp/container/node_handle).
        // It does NOT refer to the data layout of the underlying btree.
        using Base::extract;

        // btree_multiset::merge()
        //
        // Extracts all elements from a given `source` btree_multiset into this
        // `btree_multiset`.
        using Base::merge;

        // btree_multiset::swap(btree_multiset& other)
        //
        // Exchanges the contents of this `btree_multiset` with those of the `other`
        // btree_multiset, avoiding invocation of any move, copy, or swap operations
        // on individual elements.
        //
        // All iterators and references on the `btree_multiset` remain valid,
        // excepting for the past-the-end iterator, which is invalidated.
        using Base::swap;

        // btree_multiset::contains()
        //
        // template <typename K> bool contains(const K& key) const:
        //
        // Determines whether an element comparing equal to the given `key` exists
        // within the `btree_multiset`, returning `true` if so or `false` otherwise.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::contains;

        // btree_multiset::count()
        //
        // template <typename K> size_type count(const K& key) const:
        //
        // Returns the number of elements comparing equal to the given `key` within
        // the `btree_multiset`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::count;

        // btree_multiset::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
        // `btree_multiset`.
        using Base::equal_range;

        // btree_multiset::find()
        //
        // template <typename K> iterator find(const K& key):
        // template <typename K> const_iterator find(const K& key) const:
        //
        // Finds an element with the passed `key` within the `btree_multiset`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::find;

        // btree_multiset::lower_bound()
        //
        // template <typename K> iterator lower_bound(const K& key):
        // template <typename K> const_iterator lower_bound(const K& key) const:
        //
        // Finds the first element that is not less than `key` within the
        // `btree_multiset`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::lower_bound;

        // btree_multiset::upper_bound()
        //
        // template <typename K> iterator upper_bound(const K& key):
        // template <typename K> const_iterator upper_bound(const K& key) const:
        //
        // Finds the first element that is greater than `key` within the
        // `btree_multiset`.
        //
        // Supports heterogeneous lookup, provided that the set has a compatible
        // heterogeneous comparator.
        using Base::upper_bound;

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

        // btree_multiset::key_comp();
        //
        // Returns the key comparator associated with this `btree_multiset`.
        using Base::key_comp;

        // btree_multiset::value_comp();
        //
        // Returns the value comparator associated with this `btree_multiset`. The
        // keys to sort the elements are the values themselves, therefore `value_comp`
        // and its sibling member function `key_comp` are equivalent.
        using Base::value_comp;
    };

    // absl::swap(absl::btree_multiset<>, absl::btree_multiset<>)
    //
    // Swaps the contents of two `absl::btree_multiset` containers.
    template<typename K, typename C, typename A>
    void swap(btree_multiset<K, C, A>& x, btree_multiset<K, C, A>& y)
    {
        return x.swap(y);
    }

    // absl::erase_if(absl::btree_multiset<>, Pred)
    //
    // Erases all elements that satisfy the predicate pred from the container.
    // Returns the number of erased elements.
    template<typename K, typename C, typename A, typename Pred>
    typename btree_multiset<K, C, A>::size_type erase_if(
        btree_multiset<K, C, A>& set, Pred pred
    )
    {
        return container_internal::btree_access::erase_if(set, std::move(pred));
    }

    namespace container_internal
    {

        // This type implements the necessary functions from the
        // absl::container_internal::slot_type interface for btree_(multi)set.
        template<typename Key>
        struct set_slot_policy
        {
            using slot_type = Key;
            using value_type = Key;
            using mutable_value_type = Key;

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

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

            template<typename Alloc>
            static void construct(Alloc* alloc, slot_type* slot, slot_type* other)
            {
                absl::allocator_traits<Alloc>::construct(*alloc, slot, std::move(*other));
            }

            template<typename Alloc>
            static void construct(Alloc* alloc, slot_type* slot, const slot_type* other)
            {
                absl::allocator_traits<Alloc>::construct(*alloc, slot, *other);
            }

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

            template<typename Alloc>
            static void transfer(Alloc* alloc, slot_type* new_slot, slot_type* old_slot)
            {
                construct(alloc, new_slot, old_slot);
                destroy(alloc, old_slot);
            }
        };

        // A parameters structure for holding the type parameters for a btree_set.
        // Compare and Alloc should be nothrow copy-constructible.
        template<typename Key, typename Compare, typename Alloc, int TargetNodeSize, bool IsMulti>
        struct set_params : common_params<Key, Compare, Alloc, TargetNodeSize, IsMulti,
                                          /*IsMap=*/false,
                                          set_slot_policy<Key>>
        {
            using value_type = Key;
            using slot_type = typename set_params::common_params::slot_type;

            template<typename V>
            static const V& key(const V& value)
            {
                return value;
            }
            static const Key& key(const slot_type* slot)
            {
                return *slot;
            }
            static const Key& key(slot_type* slot)
            {
                return *slot;
            }
        };

    }  // namespace container_internal

    ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CONTAINER_BTREE_SET_H_