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btree_set.h (29537B)

---

// 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()`, `erase()`, and `extract_and_get_next()` return a valid
// iterator at the current position.
//
// There are other API differences: first, btree iterators can be subtracted,
// and this is faster than using `std::distance`. Additionally, btree
// iterators can be advanced via `operator+=` and `operator-=`, which is faster
// than using `std::advance`.
//
// B-tree sets are not exception-safe.

#ifndef ABSL_CONTAINER_BTREE_SET_H_
#define ABSL_CONTAINER_BTREE_SET_H_

#include "absl/base/attributes.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 ABSL_ATTRIBUTE_OWNER 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. Any references, pointers, or iterators
 // are invalidated. 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::extract_and_get_next()
 //
 // Extracts the indicated element, erasing it in the process, and returns it
 // as a C++17-compatible node handle along with an iterator to the next
 // element.
 //
 // extract_and_get_next_return_type extract_and_get_next(
 //     const_iterator position):
 //
 //   Extracts the element at the indicated position, returns a struct
 //   containing a member named `node`: a node handle owning that extracted
 //   data and a member named `next`: an iterator pointing to the next element
 //   in the btree.
 using Base::extract_and_get_next;

 // 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 ABSL_ATTRIBUTE_OWNER 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::extract_and_get_next()
 //
 // Extracts the indicated element, erasing it in the process, and returns it
 // as a C++17-compatible node handle along with an iterator to the next
 // element.
 //
 // extract_and_get_next_return_type extract_and_get_next(
 //     const_iterator position):
 //
 //   Extracts the element at the indicated position, returns a struct
 //   containing a member named `node`: a node handle owning that extracted
 //   data and a member named `next`: an iterator pointing to the next element
 //   in the btree.
 using Base::extract_and_get_next;

 // 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);
 }
};

// 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_