Creation of LTS branch "lts_2020_02_25"20200225

  - 0033c9ea91a52ade7c6b725aa2ef3cbe15463421 Fix build on FreeBSD/powerpc (#616) by kgotlinux <60880393+kgotlinux@users.noreply.github.com>
  - 0d5ce2797eb695aee7e019e25323251ef6ffc277 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - b69c7d880caddfc25bf348dbcfe9d45fdd8bc6e6 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 2a5633fc077a58528cdbfe78720f3f6bfdc6044d Merge "Export of internal Abseil changes" by Xiaoyi Zhang <zhangxy@google.com>
  - f9b3d6e493c1b6ab3dbdab71c5f8fa849db4abaf Add RISCV support to GetProgramCounter() (#621) by Khem Raj <raj.khem@gmail.com>
  - 0232c87f21c26718aa3eb2d86678070f3b498a4e Add missing ABSL_HAVE_VDSO_SUPPORT conditional (#622) by Sinan Kaya <41809318+franksinankaya@users.noreply.github.com>
  - 3c814105108680997d0821077694f663693b5382 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - c44657f55692eddf5504156645d1f4ec7b3acabd Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 98eb410c93ad059f9bba1bf43f5bb916fc92a5ea Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - bf78e977309c4cb946914b456404141ddac1c302 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - d95d1567165d449e4c213ea31a15cbb112a9865f Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 24713a7036a81498334807fa5c7ad3cb7c643711 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 72382c21fefed981b4b8a2a1b82e2d231c2c2e39 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 08a7e7bf972c8451855a5022f2faf3d3655db015 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 36bcd9599b3f48c99357ba61cf33584889306d6a Fix pointer format specifier in documentation (#614) by Andre Nguyen <andre-nguyen@users.noreply.github.com>
  - 0f86336b6939ea673cc1cbe29189286cae67d63a Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - c512f118dde6ffd51cb7d8ac8804bbaf4d266c3a Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 37dd2562ec830d547a1524bb306be313ac3f2556 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 44427702614d7b86b064ba06a390f5eb2f85dbf6 fix: Add support for more ARM processors detection (#608) by Andre Nguyen <andre-nguyen@users.noreply.github.com>
  - 159bf2bf6d1cc8087e02468d071e94d1177d1bae Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - a2e6adecc294dc4cd98cc285a9134ce58e0f2ad0 Use https links. (#586) by nlewycky <nicholas@mxc.ca>
  - 564001ae506a17c51fa1223684a78f05f91d3d91 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - b3aaac8a37c467a1125c794196caa90d0957bdc3 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 63ee2f8877915a3565c29707dba8fe4d7822596a Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - a048203a881f11f4b7b8df5fb563aec85522f8db Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 1de0166368e2ae67347f92099d6dca3ab3a4a496 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - ad904b6cd3906ddf79878003d92b7bc08d7786ae Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 29235139149790f5afc430c11cec8f1eb1677607 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - bf86cfe165ef7d70dfe68f0b8fc0c018bc79a577 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 12bc53e0318d80569270a5b26ccbc62b52022b89 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 1e39f8626a4dadec1f56920b999dd4c3cfae333e Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 77f87009a34c745255bd84d8f2647040d831a2b3 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - d659fe54b35ab9b8e35c72e50a4b8814167d5a84 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - a4b757b5d42694306a9de853cee0a5fba9c7bbe9 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 0514227d2547793b23e209809276375e41c76617 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 7f4fe64af80fe3c84db8ea938276c3690573c45e Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 16d9fd58a51c6083234e2e9f8f50e49ed5ed02e4 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - bcaae6009c0833b73c6fa7bdd972921d8081a724 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 8ba96a8244bbe334d09542e92d566673a65c1f78 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 2103fd9acdf58279f739860bff3f8c9f4b845605 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 3df7b52a6ada51a72a23796b844549a7b282f1b8 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - fa8c75182fbfdeddb2485fc0d53baeda3f40b7a3 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 85092b4b648ca729c6263c4a302a41dfff28705e Fix Conan builds (#400) by Adrian Ostrowski <adr.ostrowski@gmail.com>
  - e96ae2203b80d5ae2e0b7abe0c77b722b224b16d Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 20de2db748ca0471cfb61cb53e813dd12938c12b Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 846e5dbedac123d12455adcfe6f53c8b5dcbfeef Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 8207907f4f7fbaeeaa2b7340c76875e06fd345ba Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 078b89b3c046d230ef3ad39494e5852184eb528b Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 19b021cb3ff23048dfbe236a4e611925d8930831 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - ecc0033b54847f6c9ee37dbb0be8aa17e5b6d37b Always enable proper symbolize implementation on Windows ... by Loo Rong Jie <loorongjie@gmail.com>
  - 2796d500aea5a31d26b8b24a33fab7a1c8fa2f32 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - e4c8d0eb8ef4acb5d7a4252b3b87feb391ef7e41 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - a15364ce4d88534ae2295127e5d8e32aefb6b446 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - ab3552a18964e7063c8324f45b3896a6a20b08a8 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - e9f9000c7c80993cb589d011616b7a8016e42f4a Fix ABSL_WAITER_MODE detection for mingw (#342) by Joe Sylve <Joe.Sylve@gmail.com>
  - abea769b551f7a100f540967cb95debdb0080df8 Fix ABSL_HAVE_ALARM check on mingw (#341) by Joe Sylve <Joe.Sylve@gmail.com>
  - 25597bdfc148e91e27678ec30efa52f4fc8c164f Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - aad33fefaa8f744d71ce747a53717b835bdf8e84 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 8fe7214fe2d7a45ecc4d85f6a524c6b1532426de Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - debac94cfb5a0fa75d1d97c399682bd1c72e3191 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 882b3501a31eb0e4ae4213afb91a0e43feda7d5f Fix spelling errors (#384) by Sungmann Cho <55860394+chosungmann@users.noreply.github.com>
  - 502efe6d7841bff82b1aeef5500491fe9a48c635 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - ccdd1d57b6386ebc26fb0c7d99b604672437c124 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - ddf8e52a2918dd0ccec75d3e2426125fa3926724 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 6ec136281086b71da32b5fb068bd6e46b78a5c79 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - ac78ffc3bc0a8b295cab9a03817760fd460df2a1 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 5374c56e5196320681993869e3126b51edac2a43 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 97c1664b4bbab5f78fac2b151ab02656268fb34b Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 325fd7b042ff4ec34f7dd32e602cd81ad0e24b22 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 83c1d65c90a92aa49632b9ac5a793214bb0768bc Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - eb6b7bd23bc0815bfd784e1a74021ce166765280 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 9ddac555b7861dc178d0dbe758a1cfbed718784b Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 1948f6f967e34db9793cfa8b4bcbaf370d039fd8 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - a0d1e098c2f99694fa399b175a7ccf920762030e Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 2d2d7fbc283315b676159716376e739d3d23ed94 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 0302d1e5fa4fcdd1763b7d1bb3212943b1ae911d supppress unused variable warning for gcc (#372) by Martin <pizzard@users.noreply.github.com>
  - 262d74ba81b1fc4d71f459555cde8ecb39786d68 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - f0afae0d49af3e15a7169e019634d7719143d94d Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 0e7afdcbd24c7e5b7cab4e0217d8886f1525b520 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 9a41ffdd3a0ccbcdd29c4e3886b28e06f2cd9c66 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 36910d3d7e9fccadd6603f232d0c4f54dcd47c7e [bazel] Add fixes for --incompatible_load_cc_rules_from_b... by Yannic <contact@yannic-bonenberger.com>
  - aae8143cf9aa611f70d7ea9b95b8b8b383b2271a Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - d9aa92d7fb324314f9df487ac23d32a25650b742 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 321ab5303023c86cd15d9ddc5740fb4b4fde32e1 Export of internal Abseil changes by Abseil Team <absl-team@google.com>
  - 4ef574064e75b86f115549e9eb4c7e806781b3ab Export of internal Abseil changes by Abseil Team <absl-team@google.com>

GitOrigin-RevId: 0033c9ea91a52ade7c6b725aa2ef3cbe15463421
Change-Id: I8a2b70063cb3ab40c6943a6db0fe40cae71ed8d7

1 files changed, 759 insertions, 0 deletions

diff --git a/absl/container/btree_map.h b/absl/container/btree_map.h
new file mode 100644
index 00000000..d23f4ee5
--- /dev/null
+++ b/absl/container/btree_map.h
@@ -0,0 +1,759 @@
+// 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.
+//
+// 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_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
+
+// 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,
+              /*Multi=*/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.
+  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. 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& x):
+  //
+  //   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: 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::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 is provided 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 is provided a
+  // compatible heterogeneous comparator.
+  using Base::count;
+
+  // btree_map::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_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 is provided a
+  // compatible heterogeneous comparator.
+  using Base::find;
+
+  // 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.
+template <typename K, typename V, typename C, typename A, typename Pred>
+void erase_if(btree_map<K, V, C, A> &map, Pred pred) {
+  for (auto it = map.begin(); it != map.end();) {
+    if (pred(*it)) {
+      it = map.erase(it);
+    } else {
+      ++it;
+    }
+  }
+}
+
+// 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,
+              /*Multi=*/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& x):
+  //
+  //   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: 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::merge()
+  //
+  // Extracts elements from a given `source` btree_multimap into this
+  // `btree_multimap`. If the destination `btree_multimap` already contains an
+  // element with an equivalent key, that element is not extracted.
+  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 is provided 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 is provided a
+  // compatible heterogeneous comparator.
+  using Base::count;
+
+  // btree_multimap::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_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 is provided a
+  // compatible heterogeneous comparator.
+  using Base::find;
+
+  // 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.
+template <typename K, typename V, typename C, typename A, typename Pred>
+void erase_if(btree_multimap<K, V, C, A> &map, Pred pred) {
+  for (auto it = map.begin(); it != map.end();) {
+    if (pred(*it)) {
+      it = map.erase(it);
+    } else {
+      ++it;
+    }
+  }
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_BTREE_MAP_H_