btree_map.h - mozsearch

// 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_map.h

// -----------------------------------------------------------------------------

//

// This header file defines B-tree maps: sorted associative containers mapping

// keys to values.

//

//     * `absl::btree_map<>`

//     * `absl::btree_multimap<>`

//

// These B-tree types are similar to the corresponding types in the STL

// (`std::map` and `std::multimap`) 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::map` and `std::multimap`, which are commonly implemented using

// red-black tree nodes, B-tree maps use more generic B-tree nodes able to hold

// multiple values per node. Holding multiple values per node often makes

// B-tree maps perform better than their `std::map` counterparts, because

// multiple entries can be checked within the same cache hit.

//

// However, these types should not be considered drop-in replacements for

// `std::map` and `std::multimap` 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. Another important difference is that

// key-types must be copy-constructible.

//

// Another API difference is that btree iterators can be subtracted, and this

// is faster than using std::distance.

#ifndef ABSL_CONTAINER_BTREE_MAP_H_

#define ABSL_CONTAINER_BTREE_MAP_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, typename Data, typename Compare, typename Alloc,

          int TargetNodeSize, bool IsMulti>

struct map_params;

}  // namespace container_internal

// absl::btree_map<>

//

// An `absl::btree_map<K, V>` is an ordered associative container of

// unique keys and associated values designed to be a more efficient replacement

// for `std::map` (in most cases).

//

// Keys are sorted using an (optional) comparison function, which defaults to

// `std::less<K>`.

//

// An `absl::btree_map<K, V>` uses a default allocator of

// `std::allocator<std::pair<const K, V>>` 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_map<K, V, C, A>`.

//

template <typename Key, typename Value, typename Compare = std::less<Key>,

          typename Alloc = std::allocator<std::pair<const Key, Value>>>

class btree_map

    : public container_internal::btree_map_container<

          container_internal::btree<container_internal::map_params<

              Key, Value, Compare, Alloc, /*TargetNodeSize=*/256,

              /*IsMulti=*/false>>> {

  using Base = typename btree_map::btree_map_container;

 public:

  // Constructors and Assignment Operators

//

  // A `btree_map` supports the same overload set as `std::map`

  // for construction and assignment:

//

  // * Default constructor

//

  //   absl::btree_map<int, std::string> map1;

//

  // * Initializer List constructor

//

  //   absl::btree_map<int, std::string> map2 =

  //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};

//

  // * Copy constructor

//

  //   absl::btree_map<int, std::string> map3(map2);

//

  // * Copy assignment operator

//

  //  absl::btree_map<int, std::string> map4;

  //  map4 = map3;

//

  // * Move constructor

//

  //   // Move is guaranteed efficient

  //   absl::btree_map<int, std::string> map5(std::move(map4));

//

  // * Move assignment operator

//

  //   // May be efficient if allocators are compatible

  //   absl::btree_map<int, std::string> map6;

  //   map6 = std::move(map5);

//

  // * Range constructor

//

  //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};

  //   absl::btree_map<int, std::string> map7(v.begin(), v.end());

  btree_map() {}

  using Base::Base;

  // btree_map::begin()

//

  // Returns an iterator to the beginning of the `btree_map`.

  using Base::begin;

  // btree_map::cbegin()

//

  // Returns a const iterator to the beginning of the `btree_map`.

  using Base::cbegin;

  // btree_map::end()

//

  // Returns an iterator to the end of the `btree_map`.

  using Base::end;

  // btree_map::cend()

//

  // Returns a const iterator to the end of the `btree_map`.

  using Base::cend;

  // btree_map::empty()

//

  // Returns whether or not the `btree_map` is empty.

  using Base::empty;

  // btree_map::max_size()

//

  // Returns the largest theoretical possible number of elements within a

  // `btree_map` under current memory constraints. This value can be thought

  // of as the largest value of `std::distance(begin(), end())` for a

  // `btree_map<Key, T>`.

  using Base::max_size;

  // btree_map::size()

//

  // Returns the number of elements currently within the `btree_map`.

  using Base::size;

  // btree_map::clear()

//

  // Removes all elements from the `btree_map`. Invalidates any references,

  // pointers, or iterators referring to contained elements.

  using Base::clear;

  // btree_map::erase()

//

  // Erases elements within the `btree_map`. If an erase occurs, any references,

  // pointers, or iterators are invalidated.

  // Overloads are listed below.

//

  // iterator erase(iterator position):

  // iterator erase(const_iterator position):

//

  //   Erases the element at `position` of the `btree_map`, 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_map::insert()

//

  // Inserts an element of the specified value into the `btree_map`,

  // 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_map`. Returns a pair consisting of an

  //   iterator to the inserted element (or to the element that prevented the

  //   insertion) and a bool denoting whether the insertion took place.

//

  // std::pair<iterator,bool> insert(value_type&& value):

//

  //   Inserts a moveable value into the `btree_map`. Returns a pair

  //   consisting of an iterator to the inserted element (or to the element that

  //   prevented the insertion) and a bool denoting whether the insertion took

  //   place.

//

  // iterator insert(const_iterator hint, const 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_map::insert_or_assign()

//

  // Inserts an element of the specified value into the `btree_map` provided

  // that a value with the given key does not already exist, or replaces the

  // corresponding mapped type with the forwarded `obj` argument if a key for

  // that value already exists, returning an iterator pointing to the newly

  // inserted element. Overloads are listed below.

//

  // pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj):

  // pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj):

//

  //   Inserts/Assigns (or moves) the element of the specified key into the

  //   `btree_map`. If the returned bool is true, insertion took place, and if

  //   it's false, assignment took place.

//

  // iterator insert_or_assign(const_iterator hint,

  //                           const key_type& k, M&& obj):

  // iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj):

//

  //   Inserts/Assigns (or moves) the element of the specified key into the

  //   `btree_map` using the position of `hint` as a non-binding suggestion

  //   for where to begin the insertion search.

  using Base::insert_or_assign;

  // btree_map::emplace()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `btree_map`, provided that no element with the given key

  // already exists.

//

  // The element may be constructed even if there already is an element with the

  // key in the container, in which case the newly constructed element will be

  // destroyed immediately. Prefer `try_emplace()` unless your key is not

  // copyable or moveable.

//

  // If an insertion occurs, any references, pointers, or iterators are

  // invalidated.

  using Base::emplace;

  // btree_map::emplace_hint()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `btree_map`, using the position of `hint` as a non-binding

  // suggestion for where to begin the insertion search, and only inserts

  // provided that no element with the given key already exists.

//

  // The element may be constructed even if there already is an element with the

  // key in the container, in which case the newly constructed element will be

  // destroyed immediately. Prefer `try_emplace()` unless your key is not

  // copyable or moveable.

//

  // If an insertion occurs, any references, pointers, or iterators are

  // invalidated.

  using Base::emplace_hint;

  // btree_map::try_emplace()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `btree_map`, provided that no element with the given key

  // already exists. Unlike `emplace()`, if an element with the given key

  // already exists, we guarantee that no element is constructed.

//

  // If an insertion occurs, any references, pointers, or iterators are

  // invalidated.

//

  // Overloads are listed below.

//

  //   std::pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):

  //   std::pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):

//

  // Inserts (via copy or move) the element of the specified key into the

  // `btree_map`.

//

  //   iterator try_emplace(const_iterator hint,

  //                        const key_type& k, Args&&... args):

  //   iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args):

//

  // Inserts (via copy or move) the element of the specified key into the

  // `btree_map` using the position of `hint` as a non-binding suggestion

  // for where to begin the insertion search.

  using Base::try_emplace;

  // btree_map::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_map`

  //   does not contain an element with a matching key, this function returns an

  //   empty node handle.

//

  // NOTE: when compiled in an earlier version of C++ than C++17,

  // `node_type::key()` returns a const reference to the key instead of a

  // mutable reference. We cannot safely return a mutable reference without

  // std::launder (which is not available before C++17).

//

  // 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_map::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_map::merge()

//

  // Extracts elements from a given `source` btree_map into this

  // `btree_map`. If the destination `btree_map` already contains an

  // element with an equivalent key, that element is not extracted.

  using Base::merge;

  // btree_map::swap(btree_map& other)

//

  // Exchanges the contents of this `btree_map` with those of the `other`

  // btree_map, avoiding invocation of any move, copy, or swap operations on

  // individual elements.

//

  // All iterators and references on the `btree_map` remain valid, excepting

  // for the past-the-end iterator, which is invalidated.

  using Base::swap;

  // btree_map::at()

//

  // Returns a reference to the mapped value of the element with key equivalent

  // to the passed key.

  using Base::at;

  // btree_map::contains()

//

  // template <typename K> bool contains(const K& key) const:

//

  // Determines whether an element comparing equal to the given `key` exists

  // within the `btree_map`, returning `true` if so or `false` otherwise.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::contains;

  // btree_map::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_map`. Note that this function will return either `1` or `0`

  // since duplicate elements are not allowed within a `btree_map`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::count;

  // btree_map::equal_range()

//

  // Returns a half-open range [first, last), defined by a `std::pair` of two

  // iterators, containing all elements with the passed key in the `btree_map`.

  using Base::equal_range;

  // btree_map::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_map`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::find;

  // btree_map::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 with a key that is not less than `key` within the

  // `btree_map`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::lower_bound;

  // btree_map::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 with a key that is greater than `key` within the

  // `btree_map`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::upper_bound;

  // btree_map::operator[]()

//

  // Returns a reference to the value mapped to the passed key within the

  // `btree_map`, performing an `insert()` if the key does not already

  // exist.

//

  // If an insertion occurs, any references, pointers, or iterators are

  // invalidated. Otherwise iterators are not affected and references are not

  // invalidated. Overloads are listed below.

//

  // T& operator[](key_type&& key):

  // T& operator[](const key_type& key):

//

  //   Inserts a value_type object constructed in-place if the element with the

  //   given key does not exist.

  using Base::operator[];

  // btree_map::get_allocator()

//

  // Returns the allocator function associated with this `btree_map`.

  using Base::get_allocator;

  // btree_map::key_comp();

//

  // Returns the key comparator associated with this `btree_map`.

  using Base::key_comp;

  // btree_map::value_comp();

//

  // Returns the value comparator associated with this `btree_map`.

  using Base::value_comp;

};

// absl::swap(absl::btree_map<>, absl::btree_map<>)

//

// Swaps the contents of two `absl::btree_map` containers.

template <typename K, typename V, typename C, typename A>

void swap(btree_map<K, V, C, A> &x, btree_map<K, V, C, A> &y) {

  return x.swap(y);

// absl::erase_if(absl::btree_map<>, Pred)

//

// Erases all elements that satisfy the predicate pred from the container.

// Returns the number of erased elements.

template <typename K, typename V, typename C, typename A, typename Pred>

typename btree_map<K, V, C, A>::size_type erase_if(

    btree_map<K, V, C, A> &map, Pred pred) {

  return container_internal::btree_access::erase_if(map, std::move(pred));

// absl::btree_multimap

//

// An `absl::btree_multimap<K, V>` is an ordered associative container of

// keys and associated values designed to be a more efficient replacement for

// `std::multimap` (in most cases). Unlike `absl::btree_map`, a B-tree multimap

// allows multiple elements with equivalent keys.

//

// Keys are sorted using an (optional) comparison function, which defaults to

// `std::less<K>`.

//

// An `absl::btree_multimap<K, V>` uses a default allocator of

// `std::allocator<std::pair<const K, V>>` 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_multimap<K, V, C, A>`.

//

template <typename Key, typename Value, typename Compare = std::less<Key>,

          typename Alloc = std::allocator<std::pair<const Key, Value>>>

class btree_multimap

    : public container_internal::btree_multimap_container<

          container_internal::btree<container_internal::map_params<

              Key, Value, Compare, Alloc, /*TargetNodeSize=*/256,

              /*IsMulti=*/true>>> {

  using Base = typename btree_multimap::btree_multimap_container;

 public:

  // Constructors and Assignment Operators

//

  // A `btree_multimap` supports the same overload set as `std::multimap`

  // for construction and assignment:

//

  // * Default constructor

//

  //   absl::btree_multimap<int, std::string> map1;

//

  // * Initializer List constructor

//

  //   absl::btree_multimap<int, std::string> map2 =

  //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};

//

  // * Copy constructor

//

  //   absl::btree_multimap<int, std::string> map3(map2);

//

  // * Copy assignment operator

//

  //  absl::btree_multimap<int, std::string> map4;

  //  map4 = map3;

//

  // * Move constructor

//

  //   // Move is guaranteed efficient

  //   absl::btree_multimap<int, std::string> map5(std::move(map4));

//

  // * Move assignment operator

//

  //   // May be efficient if allocators are compatible

  //   absl::btree_multimap<int, std::string> map6;

  //   map6 = std::move(map5);

//

  // * Range constructor

//

  //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};

  //   absl::btree_multimap<int, std::string> map7(v.begin(), v.end());

  btree_multimap() {}

  using Base::Base;

  // btree_multimap::begin()

//

  // Returns an iterator to the beginning of the `btree_multimap`.

  using Base::begin;

  // btree_multimap::cbegin()

//

  // Returns a const iterator to the beginning of the `btree_multimap`.

  using Base::cbegin;

  // btree_multimap::end()

//

  // Returns an iterator to the end of the `btree_multimap`.

  using Base::end;

  // btree_multimap::cend()

//

  // Returns a const iterator to the end of the `btree_multimap`.

  using Base::cend;

  // btree_multimap::empty()

//

  // Returns whether or not the `btree_multimap` is empty.

  using Base::empty;

  // btree_multimap::max_size()

//

  // Returns the largest theoretical possible number of elements within a

  // `btree_multimap` under current memory constraints. This value can be

  // thought of as the largest value of `std::distance(begin(), end())` for a

  // `btree_multimap<Key, T>`.

  using Base::max_size;

  // btree_multimap::size()

//

  // Returns the number of elements currently within the `btree_multimap`.

  using Base::size;

  // btree_multimap::clear()

//

  // Removes all elements from the `btree_multimap`. Invalidates any references,

  // pointers, or iterators referring to contained elements.

  using Base::clear;

  // btree_multimap::erase()

//

  // Erases elements within the `btree_multimap`. If an erase occurs, any

  // references, pointers, or iterators are invalidated.

  // Overloads are listed below.

//

  // iterator erase(iterator position):

  // iterator erase(const_iterator position):

//

  //   Erases the element at `position` of the `btree_multimap`, 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_multimap::insert()

//

  // Inserts an element of the specified value into the `btree_multimap`,

  // 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_multimap`, returning an iterator to the

  //   inserted element.

//

  // iterator insert(value_type&& value):

//

  //   Inserts a moveable value into the `btree_multimap`, 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_multimap::emplace()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `btree_multimap`. Any references, pointers, or iterators are

  // invalidated.

  using Base::emplace;

  // btree_multimap::emplace_hint()

//

  // Inserts an element of the specified value by constructing it in-place

  // within the `btree_multimap`, 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_multimap::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_multimap`

  //   does not contain an element with a matching key, this function returns an

  //   empty node handle.

//

  // NOTE: when compiled in an earlier version of C++ than C++17,

  // `node_type::key()` returns a const reference to the key instead of a

  // mutable reference. We cannot safely return a mutable reference without

  // std::launder (which is not available before C++17).

//

  // 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_multimap::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_multimap::merge()

//

  // Extracts all elements from a given `source` btree_multimap into this

  // `btree_multimap`.

  using Base::merge;

  // btree_multimap::swap(btree_multimap& other)

//

  // Exchanges the contents of this `btree_multimap` with those of the `other`

  // btree_multimap, avoiding invocation of any move, copy, or swap operations

  // on individual elements.

//

  // All iterators and references on the `btree_multimap` remain valid,

  // excepting for the past-the-end iterator, which is invalidated.

  using Base::swap;

  // btree_multimap::contains()

//

  // template <typename K> bool contains(const K& key) const:

//

  // Determines whether an element comparing equal to the given `key` exists

  // within the `btree_multimap`, returning `true` if so or `false` otherwise.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::contains;

  // btree_multimap::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_multimap`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::count;

  // btree_multimap::equal_range()

//

  // Returns a half-open range [first, last), defined by a `std::pair` of two

  // iterators, containing all elements with the passed key in the

  // `btree_multimap`.

  using Base::equal_range;

  // btree_multimap::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_multimap`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::find;

  // btree_multimap::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 with a key that is not less than `key` within the

  // `btree_multimap`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::lower_bound;

  // btree_multimap::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 with a key that is greater than `key` within the

  // `btree_multimap`.

//

  // Supports heterogeneous lookup, provided that the map has a compatible

  // heterogeneous comparator.

  using Base::upper_bound;

  // btree_multimap::get_allocator()

//

  // Returns the allocator function associated with this `btree_multimap`.

  using Base::get_allocator;

  // btree_multimap::key_comp();

//

  // Returns the key comparator associated with this `btree_multimap`.

  using Base::key_comp;

  // btree_multimap::value_comp();

//

  // Returns the value comparator associated with this `btree_multimap`.

  using Base::value_comp;

};

// absl::swap(absl::btree_multimap<>, absl::btree_multimap<>)

//

// Swaps the contents of two `absl::btree_multimap` containers.

template <typename K, typename V, typename C, typename A>

void swap(btree_multimap<K, V, C, A> &x, btree_multimap<K, V, C, A> &y) {

  return x.swap(y);

// absl::erase_if(absl::btree_multimap<>, Pred)

//

// Erases all elements that satisfy the predicate pred from the container.

// Returns the number of erased elements.

template <typename K, typename V, typename C, typename A, typename Pred>

typename btree_multimap<K, V, C, A>::size_type erase_if(

    btree_multimap<K, V, C, A> &map, Pred pred) {

  return container_internal::btree_access::erase_if(map, std::move(pred));

namespace container_internal {

// A parameters structure for holding the type parameters for a btree_map.

// Compare and Alloc should be nothrow copy-constructible.

template <typename Key, typename Data, typename Compare, typename Alloc,

          int TargetNodeSize, bool IsMulti>

struct map_params : common_params<Key, Compare, Alloc, TargetNodeSize, IsMulti,

                                  /*IsMap=*/true, map_slot_policy<Key, Data>> {

  using super_type = typename map_params::common_params;

  using mapped_type = Data;

  // This type allows us to move keys when it is safe to do so. It is safe

  // for maps in which value_type and mutable_value_type are layout compatible.

  using slot_policy = typename super_type::slot_policy;

  using slot_type = typename super_type::slot_type;

  using value_type = typename super_type::value_type;

  using init_type = typename super_type::init_type;

  template <typename V>

  static auto key(const V &value) -> decltype(value.first) {

    return value.first;

  static const Key &key(const slot_type *s) { return slot_policy::key(s); }

  static const Key &key(slot_type *s) { return slot_policy::key(s); }

  // For use in node handle.

  static auto mutable_key(slot_type *s)

      -> decltype(slot_policy::mutable_key(s)) {

    return slot_policy::mutable_key(s);

  static mapped_type &value(value_type *value) { return value->second; }

};

}  // namespace container_internal

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_CONTAINER_BTREE_MAP_H_

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